Retirement Benefit Schemes - Summary of Movements in Funded Scheme Assets (Details) - GBP (£) £ in Millions	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023
Changes in Plan Assets [Abstract]
Fair value of scheme assets at 1 January	£ 7,317
Fair value of scheme assets at 31 December	6,612	£ 7,317
Fair value of scheme assets  at 31 December	6,612	7,317
Listed
Changes in Plan Assets [Abstract]
Equities	341	634
Bonds	1,205	1,156
Other assets	511	564
Unlisted
Changes in Plan Assets [Abstract]
Equities	688	724
Bonds	875	861
Buy-in insurance policies	2,345	2,585
Other assets	647	793
Plan assets
Changes in Plan Assets [Abstract]
Fair value of scheme assets at 1 January	7,317	7,424
Differences on exchange	(126)	(192)
Settlements	(203)	(60)
Interest on scheme assets	320	354
Company contributions	30	64
Contributions by scheme members	2	2
Benefits paid	(457)	(462)
Actuarial (losses)/gains	(271)	187
Fair value of scheme assets at 31 December	6,612	7,317
Fair value of scheme assets  at 31 December	6,612	7,317
Plan assets \| Pension schemes
Changes in Plan Assets [Abstract]
Fair value of scheme assets at 1 January	7,172	7,271
Differences on exchange	(128)	(182)
Settlements	(203)	(60)
Interest on scheme assets	312	345
Company contributions	30	64
Contributions by scheme members	2	2
Benefits paid	(442)	(448)
Actuarial (losses)/gains	(271)	180
Fair value of scheme assets at 31 December	6,472	7,172
Fair value of scheme assets  at 31 December	6,472	7,172
Plan assets \| Pension schemes \| Listed
Changes in Plan Assets [Abstract]
Equities	336	629
Bonds	1,180	1,139
Other assets	509	556
Plan assets \| Pension schemes \| Unlisted
Changes in Plan Assets [Abstract]
Equities	688	675
Bonds	777	803
Buy-in insurance policies	2,345	2,585
Other assets	637	785
Plan assets \| Healthcare schemes
Changes in Plan Assets [Abstract]
Fair value of scheme assets at 1 January	145	153
Differences on exchange	2	(10)
Settlements	0	0
Interest on scheme assets	8	9
Company contributions	0	0
Contributions by scheme members	0	0
Benefits paid	(15)	(14)
Actuarial (losses)/gains	0	7
Fair value of scheme assets at 31 December	140	145
Fair value of scheme assets  at 31 December	140	145
Plan assets \| Healthcare schemes \| Listed
Changes in Plan Assets [Abstract]
Equities	5	5
Bonds	25	17
Other assets	2	8
Plan assets \| Healthcare schemes \| Unlisted
Changes in Plan Assets [Abstract]
Equities	0	49
Bonds	98	58
Buy-in insurance policies	0	0
Other assets	£ 10	£ 8

Changes in Plan Assets

No definition available.

Name:	bti_ChangesInPlanAssetsAbstract
Namespace Prefix:	bti_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The decrease (increase) in a net defined benefit liability (asset) resulting from actuarial gains (losses) arising from changes in financial assumptions that result in remeasurements of the net defined benefit liability (asset). Financial assumptions deal with items such as: (a) the discount rate; (b) benefit levels, excluding any cost of the benefits to be met by employees, and future salary; (c) in the case of medical benefits, future medical costs, including claim handling costs (ie the costs that will be incurred in processing and resolving claims, including legal and adjuster's fees); and (d) taxes payable by the plan on contributions relating to service before the reporting date or on benefits resulting from that service. [Refer: Net defined benefit liability (asset)]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2024-01-01
-Paragraph 141
-Subparagraph c
-Clause iii
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2024-en-r&anchor=para_141_c_iii&doctype=Standard
-URIDate 2024-03-27

+ Details

Name:	ifrs-full_ActuarialGainsLossesArisingFromChangesInFinancialAssumptionsNetDefinedBenefitLiabilityAsset
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The decrease (increase) in net defined benefit liability (asset) resulting from contributions to a defined benefit plan by the employer. [Refer: Net defined benefit liability (asset); Defined benefit plans [domain]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2024-01-01
-Paragraph 141
-Subparagraph f
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2024-en-r&anchor=para_141_f&doctype=Standard
-URIDate 2024-03-27

+ Details

Name:	ifrs-full_ContributionsToPlanByEmployerNetDefinedBenefitLiabilityAsset
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The decrease (increase) in the net defined benefit liability (asset) resulting from contributions to a defined benefit plan by plan participants. [Refer: Net defined benefit liability (asset); Defined benefit plans [domain]]

+ References

+ Details

Name:	ifrs-full_ContributionsToPlanByPlanParticipantsNetDefinedBenefitLiabilityAsset
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount instruments representing debt (rather than equity) contribute to the fair value of defined benefit plan assets. [Refer: Plan assets, at fair value; Defined benefit plans [domain]]

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Name IAS
-Number 19
-IssueDate 2024-01-01
-Paragraph 142
-Subparagraph c
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2024-en-r&anchor=para_142_c&doctype=Standard
-URIDate 2024-03-27

+ Details

Name:	ifrs-full_DebtInstrumentsAmountContributedToFairValueOfPlanAssets
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount instruments representing equity (rather than debt) contribute to the fair value of defined benefit plan assets. [Refer: Plan assets, at fair value; Defined benefit plans [domain]]

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Name IAS
-Number 19
-IssueDate 2024-01-01
-Paragraph 142
-Subparagraph b
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2024-en-r&anchor=para_142_b&doctype=Standard
-URIDate 2024-03-27

+ Details

Name:	ifrs-full_EquityInstrumentsAmountContributedToFairValueOfPlanAssets
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The decrease (increase) in the net defined benefit liability (asset) resulting from settlements. Settlements are transactions that eliminate all further legal or constructive obligations for part or all of the benefits provided under a defined benefit plan, other than a payment of benefits to, or on behalf of, employees that is set out in the terms of the plan and included in the actuarial assumptions. [Refer: Net defined benefit liability (asset); Defined benefit plans [domain]; Actuarial assumptions [domain]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2024-01-01
-Paragraph 141
-Subparagraph d
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2024-en-r&anchor=para_141_d&doctype=Standard
-URIDate 2024-03-27

+ Details

Name:	ifrs-full_GainsLossesArisingFromSettlementsNetDefinedBenefitLiabilityAsset
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The increase (decrease) in the net defined benefit liability (asset) resulting from changes in foreign exchange rates. [Refer: Net defined benefit liability (asset)]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2024-01-01
-Paragraph 141
-Subparagraph e
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2024-en-r&anchor=para_141_e&doctype=Standard
-URIDate 2024-03-27

+ Details

Name:	ifrs-full_IncreaseDecreaseThroughChangesInForeignExchangeRatesNetDefinedBenefitLiabilityAsset
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The increase (decrease) in the net defined benefit liability (asset) resulting from the passage of time. [Refer: Interest expense; Net defined benefit liability (asset)]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2024-01-01
-Paragraph 141
-Subparagraph b
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2024-en-r&anchor=para_141_b&doctype=Standard
-URIDate 2024-03-27

+ Details

Name:	ifrs-full_InterestExpenseIncomeNetDefinedBenefitLiabilityAsset
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The amount other types of assets not separately disclosed contribute to the fair value of defined benefit plan assets. [Refer: Plan assets, at fair value; Defined benefit plans [domain]]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 19
-IssueDate 2024-01-01
-Paragraph 142
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2024-en-r&anchor=para_142&doctype=Standard
-URIDate 2024-03-27

+ Details

Name:	ifrs-full_OtherAssetsAmountContributedToFairValueOfPlanAssets
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The decrease (increase) in the net defined benefit liability (asset) resulting from payments from the plan. [Refer: Net defined benefit liability (asset)]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2024-01-01
-Paragraph 141
-Subparagraph g
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2024-en-r&anchor=para_141_g&doctype=Standard
-URIDate 2024-03-27

+ Details

Name:	ifrs-full_PaymentsFromPlanNetDefinedBenefitLiabilityAsset
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The fair value of defined benefit plan assets. Plan assets comprise assets held by a long-term employee benefit fund and qualifying insurance policies. [Refer: At fair value [member]]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 19
-IssueDate 2024-01-01
-Paragraph 57
-Subparagraph a
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2024-en-r&anchor=para_57_a&doctype=Standard
-URIDate 2024-03-27

+ Details

Name:	ifrs-full_PlanAssetsAtFairValue
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount qualifying insurance policies contribute to the fair value of defined benefit plan assets. [Refer: Plan assets, at fair value; Defined benefit plans [domain]]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 19
-IssueDate 2024-01-01
-Paragraph 8
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2024-en-r&anchor=para_8&doctype=Standard
-URIDate 2024-03-27

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 19
-IssueDate 2024-01-01
-Paragraph 142
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=19&code=ifrs-tx-2024-en-r&anchor=para_142&doctype=Standard
-URIDate 2024-03-27

+ Details

Name:	ifrs-full_QualifyingInsurancePoliciesAmountContributedToFairValueOfPlanAssets
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	bti_DefinedBenefitPlanAssetsQuotedAndUnquotedAxis=bti_ListedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	bti_DefinedBenefitPlanAssetsQuotedAndUnquotedAxis=bti_UnlistedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_NetDefinedBenefitLiabilityAssetAxis=ifrs-full_PlanAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_DefinedBenefitPlansAxis=ifrs-full_PensionDefinedBenefitPlansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_DefinedBenefitPlansAxis=ifrs-full_PostemploymentMedicalDefinedBenefitPlansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: