Exhibit 99.1

National Grid USA Companies’

Incentive Thrift Plan I

Statements of Net Assets Available for Benefits as of December 31, 2020 and 2019 and Statement of Changes in Net Assets Available for Benefits for the Year Ended December 31, 2020

Supplemental Schedule as of December 31, 2020 and Report of Independent Registered Public Accounting Firm

Contents

Report of Independent Registered Public Accounting Firm	1-2
Financial Statements
Statements of Net Assets Available for Benefits as of December 31, 2020 and 2019	3
Statement of Changes in Net Assets Available for Benefits for the Year Ended December 31, 2020	4
Notes to Financial Statements	5 – 15
Supplemental Schedule:
Form 5500, Schedule H, Part IV, Line 4i – Schedule of Assets (Held at End of Year)	16

NOTE: All other schedules required by Section 2520.103-10 of the Department of Labor’s Rules and Regulations for Reporting and Disclosure under the Employee Retirement Income Security Act of 1974 have been omitted because they are not applicable.

REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

Retirement Plans Committee and Plan Participants

National Grid USA Companies’

    Incentive Thrift Plan I

Brooklyn, New York

Opinion on the Financial Statements

We have audited the accompanying statements of net assets available for benefits of National Grid USA Companies’ Incentive Thrift Plan I (the Plan) as of December 31, 2020 and 2019, the related statement of changes in net assets available for benefits for the year ended December 31, 2020, and the related notes and schedule (collectively referred to as the financial statements). In our opinion, the financial statements present fairly, in all material respects, the net assets available for benefits of National Grid USA Companies’ Incentive Thrift Plan I as of December 31, 2020 and 2019, and the changes in net assets available for benefits for the year ended December 31, 2020, in conformity with accounting principles generally accepted in the United States of America.

Basis for Opinion

These financial statements are the responsibility of the Plan’s management. Our responsibility is to express an opinion on the Plan’s financial statements based on our audits. We are a public accounting firm registered with the Public Company Accounting Oversight Board (United States) (PCAOB) and are required to be independent with respect to the Plan in accordance with the U.S. federal securities laws and the applicable rules and regulations of the Securities and Exchange Commission and the PCAOB.

We conducted our audits in accordance with the standards of the PCAOB. Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the financial statements are free of material misstatement, whether due to error or fraud. The Plan is not required to have, nor were we engaged to perform, an audit of its internal control over financial reporting. As part of our audits, we are required to obtain an understanding of internal control over financial reporting, but not for the purpose of expressing an opinion on the effectiveness of the Plan’s internal control over financial reporting. Accordingly, we express no such opinion.

Our audits included performing procedures to assess the risks of material misstatement of the financial statements, whether due to error or fraud, and performing procedures that respond to those risks. Such procedures included examining, on a test basis, evidence regarding the amounts and disclosures in the financial statements. Our audits also included evaluating the accounting principles used and significant estimates made by management, as well as evaluating the overall presentation of the financial statements. We believe that our audits provide a reasonable basis for our opinion.

Retirement Plans Committee and Plan Participants

National Grid USA Companies

    Incentive Thrift Plan I

Supplemental Information

The supplemental schedule of assets (held at end of year) (supplemental information) has been subjected to audit procedures performed in conjunction with the audit of the Plan’s financial statements. The supplemental information is the responsibility of the Plan’s management. Our audit procedures included determining whether the supplemental information reconciles to the financial statements or the underlying accounting and other records, as applicable, and performing procedures to test the completeness and accuracy of the information presented in the supplemental information. In forming our opinion on the supplemental information, we evaluated whether the supplemental information, including its form and content, is presented in conformity with the Department of Labor’s Rules and Regulations for Reporting and Disclosure under the Employee Retirement Income Security Act of 1974. In our opinion, the supplemental information is fairly stated, in all material respects, in relation to the financial statements as a whole.

CliftonLarsonAllen LLP

We have served as the Plan’s auditor since 2007.

Phoenix, Arizona

June 24, 2021

National Grid USA Companies’ Incentive Thrift Plan I

Statements of Net Assets Available for Benefits

December 31, 2020 and 2019

	2020		2019
Assets
Investments, at fair value	$	2,572,541,325	$	2,294,296,403
Plan interest in Master Trust		324,173,456		263,297,415
Receivables:
Notes receivable from participants		25,415,328		25,213,565
Employer contributions receivable		1,152,828		2,431,002
Dividends		2,248,540		2,271,754
Total receivables		28,816,696		29,916,321
Net assets available for benefits	$	2,925,531,477	$	2,587,510,139

The accompanying notes are an integral part of the financial statements.

3

National Grid USA Companies’ Incentive Thrift Plan I

Statement of Changes in Net Assets Available for Benefits

Year Ended December 31, 2020

Changes in net assets attributed to:
Investment income:
Net appreciation in fair value of investments	$	308,488,813
Interest and dividend income		10,761,125
Net investment income from Master Trust		6,944,155
Other additions		3,280,317
Total investment income		329,474,410
Interest income on participant notes receivable		1,109,767
Contributions:
Employee contributions		92,355,642
Employer contributions		50,293,472
Rollover contributions		10,109,363
Total contributions		152,758,477
Distributions:
Benefits paid to participants		(153,272,591	)
Fees		(642,871	)
Total distributions		(153,915,462	)
Net increase before transfer of assets from a related Plan		329,427,192
Net transfer of assets from Thrift Plan II		8,594,146
Net assets available for benefits:
Beginning of year		2,587,510,139
End of year	$	2,925,531,477

The accompanying notes are an integral part of the financial statements.

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National Grid USA Companies’ Incentive Thrift Plan I

Notes to Financial Statements

December 31, 2020 and 2019

Note 1. Description of the Plan

The following description of the National Grid USA Companies’ Incentive Thrift Plan I (the “Plan”) provides only general information. Participants should refer to the Plan document for a more complete description of the Plan’s provisions.

Plan Description

The Plan was established effective January 1, 1980, pursuant to the authorization of the Board of Directors of certain subsidiaries of the New England Electric System (“NEES”), to provide a long-range program of systematic savings for eligible employees (the “Participants”). The Plan was renamed National Grid USA Companies’ Incentive Thrift Plan I upon the merger between National Grid plc and NEES on March 22, 2000, at which time NEES was renamed National Grid USA.

Employees of participating subsidiaries of National Grid USA (collectively, the “Employers” or the “Company”) are immediately eligible to participate in the Plan upon employment, but will not receive Employer Matching Contributions (“Matching Contributions”) from the Employers until the first of the month following three months of service. Certain individuals are not eligible to participate in the Plan, including but not limited to leased employees, interns, co-op students, summer students, and independent contractors or individuals paid by an agency or party other than the Company, or any employee covered under a collective bargaining agreement.

The Plan was prepared in conformity with the Employee Retirement Income Security Act of 1974 (“ERISA”).

The plan administrators are the Retirement Plans Committee of National Grid USA Service Company, Inc. (the “Administrator”). The Board of Directors of National Grid plc has the governing authority to amend the Plan, but has delegated certain amending authority to the Board of Directors of National Grid USA Service Company, Inc. (“Service Company”).

Vanguard serves as record keeper of the Plan. The Vanguard Fiduciary Trust Company is trustee and custodian for all assets and Participant accounts with the exception of the Master Trust. Wells Fargo Bank, N.A. (“Wells Fargo”) is the Master Trustee and custodian for the assets of the Plan related to investments in the Galliard Stable Value Fund.

Effective January 1, 2019 the Plan adopted a safe harbor design for hardship distributions. The Plan was amended to provide participants with a true up Matching Contribution for 2019 plan year and thereafter, if the participant is employed on the last day of the plan year, including participants who had hardship withdrawals during the year.

Effective April 6, 2019, new contributions to the National Grid Share Fund will only be permitted if a participant’s investment in the fund is less than 20% of their account balance. If a participant was invested in more than 20% as of effective date, they may maintain their current investment but cannot make future contributions or exchanges until they fall below the 20% threshold. This restriction does not apply to reinvestment of dividends. On or after April 6, 2019, any contributions or exchanges directed to this fund that exceed 20% will be redirected to the plans’ Qualified Default Investment Alternative (“QDIA”) and participants may then redirect to any other fund except the National Grid Share Fund.

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National Grid USA Companies’ Incentive Thrift Plan I

Notes to Financial Statements

December 31, 2020 and 2019

Effective April 6, 2019, participants may invest up to 95% of their account in a self-directed brokerage option offered by the plan. Investments are limited to mutual funds not already offered in the plan. Loans and distributions are not permitted from the self-directed brokerage account until the participant sells their holdings and transfers the proceeds to the plan’s core investment options. However, the self-directed brokerage account balances will be included in the calculation to determine the loan amount available.

Effective January 1, 2020, an amendment was made to the hardship withdrawal terms requiring written representation from a participant stating that he or she has insufficient cash or other liquid assets available to satisfy an immediate and heavy financial need.

The Setting Every Community Up for Retirement Enhancement (“SECURE Act”) was signed into law on December 20, 2019. The Plan has adopted certain provisions of the SECURE Act effective January 1, 2020.

The Coronavirus Aid Relief, and Economic Security Act (“CARES Act”) was passed by the U.S. Senate on March 26, 2020. The Plan adopted certain temporary loan and distribution provisions allowed by the CARES Act through December 31, 2020.

Effective April 1, 2020, certain plan recordkeeping fees paid by participants were reduced and new distributions fees were added to the Plan.

The Plan has evaluated subsequent events for recognition or disclosure through June 24, 2021, the date the financial statements were issued.

Contributions

The Plan is a defined contribution plan. An eligible employee can make Elective Contributions through Contribution Agreements (also known as “Salary Reduction Agreements” or “Elective Contributions”) to have from 1 percent to 50 percent of their eligible compensation contributed to the Plan on their behalf. Participants can choose whether their Elective Contributions to the Plan will be calculated on their Base Pay or All Pay.

Base Pay is defined as the Participant’s regular pay, prior to any salary reductions for Elective Contributions to the Thrift Plan, and any other salary reductions under the Health Care Spending Account, Health Savings Account, Dependent Care Reimbursement Account or for Company health care coverage.

Base Pay excludes all other forms of compensation, including supplemental disability income, amounts deferred under other plans, reimbursements of expenses, incentive pay, commissions, options, payments made in lieu of vacation days or under short- or long-term disability provisions, awards, overtime, premiums, and any other additional forms of earnings (including Company contributions to or under any other employee benefit plan, such as health insurance, pension, or severance pay).

All Pay is Base Pay, as defined above, plus overtime, commissions, premium pay, and any incentive pay.

6

National Grid USA Companies’ Incentive Thrift Plan I

Notes to Financial Statements

December 31, 2020 and 2019

The annual employee pre-tax Elective Contributions by each Participant were subject to Internal Revenue Service (“IRS”) limits of $19,500 and $19,000 in 2020 and 2019, respectively, for employees who did not attain age 50 by the end of the plan year. For employees who did attain age 50 by the last day of the plan year, the annual maximum pre-tax contribution was $26,000 and $25,000 for 2020 and 2019, respectively.

Participants can also elect to contribute up to 15 percent of their pay on an after-tax basis. The total amount of Elective Contributions (pre-tax and after-tax) may not exceed 50 percent of pay (further subject to the combined IRS annual contribution limit, adjusted periodically by law, which was $57,000 for 2020 and $56,000 for 2019).

New employees with funds held under a previous employer’s qualified plan are permitted to roll over eligible amounts from such funds into the Plan.

Participants may allocate their account balances in any whole percentage without restriction on the frequency of subsequent reallocations subject to investment fund short-term trading restrictions.

Active or former employees who are Participants and who receive a lump sum distribution from a Company qualified pension plan (National Grid USA Companies’ Final Average Pay Pension Plan, Niagara Mohawk Pension Plan, KeySpan Retirement Plan and Retirement Income Plan of KeySpan Corporation) may roll the lump sum proceeds into the Plan to the extent the proceeds qualify for rollover under the Internal Revenue Code (“IRC”). The total amount rolled over from these Plans in 2020 was $1,153,388.

Company Core Contributions

Participants hired or rehired on January 1, 2011 or later are eligible for Company Core Contributions, which begin the 1st of the month following 3 months of service. The Company calculates a Participant’s Core Contribution each payroll period, based on actual compensation for that payroll period. The contribution is a percentage of pay based on the Participant’s total points as set forth in the plan documents as of January 1 of the plan year. The contribution schedule is as follows:

Points	Core Contribution (% of Pay)
< 45	4%
45 - 54	5%
55 - 64	6%
65 - 74	7%
75 +	8%

Core Contributions are based on All Pay. Participants will have an account established for them at Vanguard. Core contributions will be made to the account even if Participants do not contribute to the Plan.

Unless elected otherwise, Core Contributions will be automatically invested in the Qualified Default Investment Alternative which is the Vanguard Target Retirement Trust Select closest to the year in which the Participant will attain age 65. Once enrolled, Participants can change the investment allocation at any time.

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National Grid USA Companies’ Incentive Thrift Plan I

Notes to Financial Statements

December 31, 2020 and 2019

Company Matching Contributions

The Company matches 50 percent of the first 8 percent Participants contribute (pre-tax and after-tax contributions) to the Plan up to the annual IRS compensation limit. Matching Contributions are based on All Pay, as a ratio of the Participant’s Elective Contribution dollar amount and their All Pay. All Matching Contributions are invested in the same investments elected by the Participant for their employee contributions unless otherwise directed by the Participant. The Company performs an annual “true-up” calculation following the end of each year to determine the maximum amount of Company Matching Contributions based on participant’s contributions made over the entire year. If any amount is due, it is deposited into the participant’s account.

Automatic Enrollment

New hires are automatically enrolled 45 days after the hire date at 6 percent of their All Pay. Participant contributions will be defaulted to the Plan’s QDIA if a Participant does not select their own investments. The automatic enrollment can be reversed within the first 90 days of the enrollment date and all money in the account returned to the Participant. After the first 90 days of enrollment, the automatic enrollment can be reversed but any money already contributed to the account cannot be returned to the Participant.

Automatic Increase

Participants may elect an automatic increase of 1 to 3 percent of their pre-tax Contributions each year. A participant can elect to make the automatic increase effective at any time during the year and is capped at 50 percent of eligible compensation. It is not available for after-tax Contributions.

Participant Accounts

Each Participant’s account is credited with the Participant’s Contribution, allocations of (a) the Matching Contributions, (b) Company Core contributions (if applicable), and (c) allocations of plan earnings, net of fees. Allocations are based on Participant earnings, account balances or specific participant transactions, as defined. The benefit to which a Participant is entitled is the benefit that can be provided from the Participant’s vested account.

Vesting

Participants are immediately vested in their Elective Contributions plus actual earnings thereon. Upon termination of employment (if you are vested) or upon the determination of an employee’s disability being total and permanent, a Participant or a Participant’s beneficiary (in the case of death) is entitled to receive the full amount in the Participant’s account. Participants will be 100 percent vested in employer match, Company Core, and employer non-elective contributions on the earlier to occur of: (i) the Participant’s completion of three (3) years of service with the Company; (ii) the Participant’s attainment of Normal Retirement Age (age 65) (iii) the death of the Participant; (iv) the disability of the Participant if the Participant is receiving disability benefits under Title II of the Social Security Act; or (v) the termination or partial termination of the Plan.

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National Grid USA Companies’ Incentive Thrift Plan I

Notes to Financial Statements

December 31, 2020 and 2019

Notes Receivable from Participants

An employee can obtain a loan from the Plan from such Participant’s account. The minimum loan allowed is $1,000. A loan cannot exceed the lesser of 50 percent of the Participant’s account balance or $50,000. The $50,000 limit is further limited by the Participant’s highest outstanding loan balance within the twelve months preceding the loan request. The loans are secured by the balance in the Participant’s account. Loans must be repaid over a period of one to five years (up to fifteen years for the purchase of a primary residence) by means of payroll deductions. The loan interest rate is set at the time Participants apply for a loan based on the rate established by the Administrator. Interest rates at December 31, 2020 ranged from 3.25 percent to 10.50 percent. Participants who leave the Company or are on an unpaid leave of absence can continue to repay their outstanding loan balance through the remaining amortization period directly to Vanguard.

A default of the loan will occur if the loan balance is not paid off by the end of the quarter following the quarter in which the missed payment was due or the loan is not paid in full by the contractual maturity date. In the event of default, the outstanding balance of the loan and any unpaid accrued interest is deemed to have been distributed to the Participant. Interest continues to be tracked following a default solely for determining the amount available for a subsequent loan. Deemed distributions are included in the Loan Fund’s investment balance until the employee has been terminated. Upon termination the defaulted loan balance is deducted from the Plan. There were cumulative deemed distributions of $536,445 and $501,502 as of December 31, 2020 and 2019, respectively.

Payment of Benefits

Participants qualify for a distribution of their entire account balance when the Participant ends employment (including at retirement), becomes totally and permanently disabled or reaches age 59 1/2. Participants who qualify for a distribution may receive an immediate lump sum, defer payment, or receive the value of their account in cash installments. If a Participant defers receipt of benefits, their funds will remain invested in the investment funds of their choice. They may make investment transfers in the same manner as any active Participant.

The Plan allows automatic lump-sum distributions if the value of the Participant’s vested account balance is less than $1,000 and the Participant is no longer employed by the Company. The Participant must consent to the distribution if the present value is more than $1,000.

Unless Participants choose otherwise, their account balance remains in the Plan until they attain age 72. At that time, Participants are required to receive minimum required distributions beginning on April 1 of the following year. Participants can elect a total or partial distribution from their account(s) at any time following separation of service. In addition, Participants may: 1) receive account balances in annual, semi-annual, quarterly or monthly installments, to be paid over a period not to exceed their life expectancy. Once installments begin, the amount of each payment is determined by dividing the Participant account balance at the time of payment by the number of installments remaining to be paid; 2) receive account balances in a series of substantially equal periodic payments (paid at least annually for their life expectancy); or 3) elect to receive distributions in any amount a Participant wishes, beginning and ending at their discretion.

The Plan allows Qualified Non-elective Contributions to the extent such contributions are necessary to satisfy the nondiscrimination requirement under the Internal Revenue Code (“IRC”). Following separation from service prior to age 55, a Participant may elect to receive a partial distribution from his or her account or a total distribution at any time; such Participant may also defer receipt of his or her benefit until the latest date permitted under the IRC.

9

National Grid USA Companies’ Incentive Thrift Plan I

Notes to Financial Statements

December 31, 2020 and 2019

Forfeitures

Forfeiture accounts are maintained to hold any Employer contributions and earnings thereon that were deposited as a result of a Participant’s separation from service prior to becoming fully vested. In addition, forfeitures from prior plan mergers and uncashed Participant checks are held in the Plan forfeiture accounts.

As of December 31, 2020 and 2019, forfeited non-vested accounts totaled $791,192 and $634,834, respectively. These accounts may be used to reduce future Employer contributions and pay plan administration expenses as described in the plan document. During the year ended December 31, 2020, $1,975,094 of forfeited non-vested accounts were used to reduce Employer contributions.

Note 2. Summary of Significant Accounting Policies

Basis of Accounting

The financial statements of the Plan have been prepared on the accrual basis of accounting.

Use of Estimates

The preparation of financial statements in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, and changes therein, and disclosure of contingent assets and liabilities. Actual results could differ from those estimates.

Investment Valuation and Income Recognition

Investments are reported at fair value. Fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The Plan’s Investment Committee determines the Plan’s valuation policies utilizing information provided by the trustees. See Note 9 for discussion of fair value measurements.

Purchases and sales of securities are recorded on a trade-date basis. Interest income is recorded on the accrual basis. Dividends are recorded on the ex-dividend date. Net appreciation includes the gains and losses on investments bought and sold as well as held during the year.

Expenses

Management fees and operating expenses are charged to plan Participants and are reflected as a reduction of investment return in each of the investment options of the Plan. Such management fees and operating expenses are deducted from income earned on a daily basis. Fees related to the administration of notes receivable from participants are charged directly to the participant’s account and are included in administrative expenses.

Notes Receivable from Participants

Notes receivable from Participants are measured at their unpaid principal balance plus any accrued but unpaid interest. Related fees are recorded as administrative expenses and are expensed when they are incurred. Interest income is recorded on the accrual basis. No allowance for credit losses has been recorded as of December 31, 2020 and 2019.

10

National Grid USA Companies’ Incentive Thrift Plan I

Notes to Financial Statements

December 31, 2020 and 2019

Payment of Benefits

Benefit payments to, and withdrawals by Participants, are recorded when paid.

Note 3. Plan Termination

Although it has not expressed any intent to do so, the Company has the right to discontinue its contributions at any time and to terminate the Plan subject to the provisions of ERISA. In the event of plan termination, any unallocated assets of the Plan will be allocated to Participant accounts and distributed in such a manner as the Company may determine, and participants will become 100 percent vested in their Company contributions.

Note 4. Tax Status

The IRS has determined and informed the Company by a letter dated October 18, 2017, that the Plan was designed in accordance with applicable sections of the IRC. The Plan has since been amended, however, the plan administrator and the Plan’s counsel believe that the Plan is designed and currently being operated in compliance with the applicable requirements of the IRC. Therefore, no provision for income taxes has been included in the Plan’s financial statements. To the best of its knowledge, the Company believes that the Plan is currently in compliance with the provisions of the IRC.

U.S. GAAP requires management to evaluate tax positions taken by the Plan and recognize a tax liability if the Plan has taken an uncertain position that more likely than not would not be sustained upon examination by the IRS. The Plan is subject to routine audits by taxing jurisdictions; however, there are currently no audits for any tax periods in progress.

Note 5. Related Party and Party-In-Interest Transactions

Section 3(14) of ERISA defines a party-in-interest to include among others, fiduciaries or employees of the Plan, any person who provides services to the Plan or an employer whose employees are covered by the Plan. Accordingly, loans to Participants and investments in American Depositary Receipts of National Grid plc are considered party in interest transactions. Moreover, the Plan’s investment options include mutual funds and collective trust funds managed by Vanguard.

Certain administrative functions are performed by officers or employees of the Company. No such officer or employee receives compensation from the Plan.

Note 6. Administration of Plan Assets

The trustees of the Plan hold the Plan’s assets. Contributions are held and managed by the trustees, who invest cash received, interest and dividend income and make distributions to Participants.

Note 7. Plan Administrative and Consulting Expenses

Some administrative expenses for the Plan are paid by the Company. The trustee was paid $556,124 in administration fees out of plan assets for administering and consulting related to the Plan during the year ended December 31, 2020.

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National Grid USA Companies’ Incentive Thrift Plan I

Notes to Financial Statements

December 31, 2020 and 2019

Note 8. Master Trust

A portion of the Plan’s investments are in the Master Trust, which was established for the investment of assets of the Plan and the National Grid USA Companies’ Incentive Thrift Plan II. Each participating retirement plan has a divided interest in the Master Trust. The assets of the Master Trust are held by Wells Fargo.

The value of the Plan’s interest in the Master Trust is based on the beginning of the year value of the Plan’s interest in the trust plus actual contributions and allocated investment income less actual distributions and allocated administrative expenses. Investment income and administrative expenses relating to the Master Trust are allocated to the individual plans based upon the amount of the time the Plan’s assets were invested in the Master Trust.

The following table presents the net assets of the Master Trust as of December 31, 2020 and 2019:

	December 31, 2020
	Master Trust Balances		Plan’s Interest in Master Trust Balances
Investments, at fair value:
Collective Trust Fund	$	691,727,796	$	324,301,781
Accrued expenses		273,714		128,325
Total	$	691,454,082	$	324,173,456
	December 31, 2019
	Master Trust Balances		Plan’s Interest in Master Trust Balances
Investments, at fair value:
Collective Trust Fund	$	568,346,910	$	263,399,555
Accrued expenses		220,391		102,140
Total	$	568,126,519	$	263,297,415

The following table summarizes the net investment income of the Master Trust for the year ended December 31, 2020:

	2020
Investment income:
Interest income	$	14,918,427

Refer to Note 9 for description of the valuation methodologies used.

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National Grid USA Companies’ Incentive Thrift Plan I

Notes to Financial Statements

December 31, 2020 and 2019

The following table sets forth by level, within the fair value hierarchy, the Master Trust’s assets at fair value as of December 31, 2020 and 2019:

	Master Trust Assets at Fair Value as of December 31, 2020
	Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
Collective trust fund	$	—	$	324,301,781	$	—	$	324,301,781
	Master Trust Assets at Fair Value as of December 31, 2019
	Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
Collective trust fund	$	—	$	263,399,555	$	—	$	263,399,555

Note 9. Fair Value Measurements

The framework for measuring fair value provides a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1) and the lowest priority to unobservable inputs (Level 3). The three levels of the fair value hierarchy under authoritative guidance are described as follows:

Level 1 - Inputs to the valuation methodology are unadjusted quoted prices for identical assets or liabilities in active markets that the Plan has the ability to access.

Level 2 - Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly, such as:

• quoted prices for similar assets or liabilities in active markets;

• quoted prices for identical or similar assets or liabilities in inactive markets;

• inputs other than quoted prices that are observable for the asset or liability;

• inputs that are derived principally from or corroborated by observable market data by correlation or other means.

If the asset or liability has a specified (contractual) term, the Level 2 input must be observable for substantially the full term of the asset or liability.

Level 3 - Inputs to the valuation methodology are unobservable and significant to the fair value measurement.

The asset or liability’s fair value measurement level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. Valuation techniques maximize the use of relevant observables and minimize the use of unobservable inputs.

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National Grid USA Companies’ Incentive Thrift Plan I

Notes to Financial Statements

December 31, 2020 and 2019

The following is a description of the valuation methodologies used for assets measured at fair value. There have been no changes in methodologies used at December 31, 2020 or 2019:

Common stock: Investments in the National Grid American Depositary Receipts (which trades on the New York Stock Exchange (“NYSE” under the symbol “NGG”) are valued according to the closing price on the NYSE.

Mutual funds are valued at the daily closing prices as reported by the funds. Mutual funds held by the Plan are open-end mutual funds that are registered with the Securities and Exchange Commission. These funds are required to publish their daily net asset value (“NAV”) and to transact at that price. The mutual funds held by the Plan are deemed to be actively traded.

The collective trusts are valued at the NAV of units of the bank collective trust. NAV is a readily determinable fair value and is the basis for current transactions. Participant transactions (purchases and sales) may occur daily. If the Plan initiates a full redemption of the collective trust, the issuer reserves the right to temporarily delay withdrawal from the trust in order to ensure that securities liquidations will be carried out in an orderly business manner.

Self-directed brokerage funds consist primarily of mutual funds that are valued at the daily closing prices as reported by the funds. Additionally, there is an FDIC insured interest bearing deposit account.

The following tables set forth by level, within the fair value hierarchy, the Plan’s assets at fair value as of December 31, 2020 and 2019 excluding the Plan’s interest in the Master Trust:

	Assets at Fair Value as of December 31, 2020
	Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
Collective trust funds	$	—	$	2,362,458,172	$	—	$	2,362,458,172
Common stock		117,169,908		—		—		117,169,908
Mutual funds		76,306,831		—		—		76,306,831
Self-directed brokerage funds		16,606,414		—		—		16,606,414
Total investments subject to the fair value hierarchy	$	210,083,153	$	2,362,458,172	$	—	$	2,572,541,325

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National Grid USA Companies’ Incentive Thrift Plan I

Notes to Financial Statements

December 31, 2020 and 2019

	Assets at Fair Value as of December 31, 2019
	Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
Collective trust funds	$	—	$	2,091,316,970	$	—	$	2,091,316,970
Common stock		137,057,610		—		—		137,057,610
Mutual funds		62,187,310		—		—		62,187,310
Self-directed brokerage funds		3,734,513		—		—		3,734,513
Total investments subject to the fair value hierarchy	$	202,979,433	$	2,091,316,970	$	—	$	2,294,296,403

Note 10. Risks and Uncertainties

The Plan invests in various investment securities. Investment securities are exposed to various risks, such as interest rate, market and credit risks. Due to the level of risk associated with certain investment securities, it is at least reasonably possible that changes in the values of investment securities will occur in the near term and that such changes could materially affect Participants’ account balances and the amounts reported in the Statements of Net Assets Available for Benefits.

Note 11. Reconciliation of Financial Statements to Form 5500

The following is a reconciliation of net assets available for benefits per the financial statements to the Form 5500 as of December 31, 2020 and 2019:

	2020			2019
Net assets available for benefits per the financial statements	$	2,925,531,477		$	2,587,510,139
Less deemed distributions		(536,445	)		(501,502	)
Net assets available for benefits per the Form 5500	$	2,924,995,032		$	2,587,008,637

The following is reconciliation of the change in net assets per the financial statements to the Form 5500 for the year ended December 31, 2020:

	2020
Change in net assets available for benefits per the financial statements	$	329,427,192
Change in cumulative deemed distributions		(34,943	)
Change in net assets available for benefits per the Form 5500	$	329,392,249

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National Grid USA Companies’ Incentive Thrift Plan I

Form 5500, Schedule H, Part IV, Line 4i - Schedule of Assets (Held at End of Year)

December 31, 2020

Plan #005 EIN: 04-1663150

(a)	(b) Identity of Issuer, borrower, lessor or similar party	(c) Description of Investment, including maturity date, rate of interest, collateral, par or maturity value	(d) Cost**	(e) Current Value
	Mutual funds:
	PIMCO Total Return Fund; Institutional Class	Mutual fund; 7,198,758 shares		$	76,306,831
	Total mutual funds				76,306,831
	Collective trust funds:
	T. Rowe Price Retirement 2005 Trust; Class F	Collective trust fund; 97,536 units			1,803,436
	T. Rowe Price Retirement 2010 Trust; Class F	Collective trust fund; 76,532 units			1,493,145
	T. Rowe Price Retirement 2015 Trust; Class F	Collective trust fund; 62,178 units			1,310,092
	T. Rowe Price Retirement 2020 Trust; Class F	Collective trust fund; 669,304 units			15,179,806
	T. Rowe Price Retirement 2025 Trust; Class F	Collective trust fund; 451,277 units			10,997,624
	T. Rowe Price Retirement 2030 Trust; Class F	Collective trust fund; 1,185,870 units			30,749,621
	T. Rowe Price Retirement 2035 Trust; Class F	Collective trust fund; 57,104 units			1,552,658
	T. Rowe Price Retirement 2040 Trust; Class F	Collective trust fund; 610,806 units			17,194,189
	T. Rowe Price Retirement 2045 Trust; Class F	Collective trust fund; 66,865 units			1,901,638
	T. Rowe Price Retirement 2050 Trust; Class F	Collective trust fund; 347,884 units			9,890,334
	T. Rowe Price Retirement 2055 Trust; Class F	Collective trust fund; 15,054 units			427,672
	T. Rowe Price Retirement 2060 Trust; Class F	Collective trust fund; 94,331 units			1,714,929
*	Vanguard Institutional 500 Index Trust	Collective trust fund; 2,044,462 units			274,325,886
*	Vanguard Institutional Extended Market Index Trust	Collective trust fund; 1,071,264 units			152,590,886
*	Vanguard Institutional Total Bond Market Index Trust	Collective trust fund; 444,162 units			50,709,971
*	Vanguard Institutional Total International Stock Market Index	Collective trust fund; 449,840 units			55,393,279
*	Vanguard Target Retirement 2015 Trust Select	Collective trust fund; 2,321,685 units			99,205,619
*	Vanguard Target Retirement 2020 Trust Select	Collective trust fund; 4,249,830 units			190,987,358
*	Vanguard Target Retirement 2025 Trust Select	Collective trust fund; 7,686,124 units			357,635,334
*	Vanguard Target Retirement 2030 Trust Select	Collective trust fund; 7,777,617 units			369,903,465
*	Vanguard Target Retirement 2035 Trust Select	Collective trust fund; 4,058,453 units			197,159,665
*	Vanguard Target Retirement 2040 Trust Select	Collective trust fund; 2,408,201 units			119,230,050
*	Vanguard Target Retirement 2045 Trust Select	Collective trust fund; 2,209,645 units			111,100,955
*	Vanguard Target Retirement 2050 Trust Select	Collective trust fund; 2,303,256 units			115,922,853
*	Vanguard Target Retirement 2055 Trust Select	Collective trust fund; 1,251,164 units			62,921,015
*	Vanguard Target Retirement 2060 Trust Select	Collective trust fund; 591,632 units			29,788,659
*	Vanguard Target Retirement 2065 Trust Select	Collective trust fund; 177,263 units			5,363,989
*	Vanguard Target Retirement Income Trust Select	Collective trust fund; 1,834,074 units			76,004,044
	Total collective trust funds				2,362,458,172
	Self-directed brokerage funds:
	Self-directed brokerage funds	SDBF; 16,606,414 shares/units			16,606,414
	Total self-directed brokerage fund				16,606,414
	Common Stock:
*	National Grid American Depository Receipt Fund	Common stock; 1,984,921 units			117,169,908
	Total common stock				117,169,908
	Total investments per financial statements				2,572,541,325
*	Notes receivable from participants	Loans to participants with various maturities and rates of interest from 3.25% to 8.5%			24,878,883
	Total investments per Form 5500			$	2,597,420,208

* Represents a party-in-interest as defined by ERISA.

** All investments are participant-directed; therefore cost information has not been presented.

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