Share Capital and Share Premium (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure Of Classes Of Share Capital [Abstract]

Summary of Share Capital and Share Premium

	2017		2016		2015
	(in thousands)
	£		£		£
Share capital		1,272		663		659
Share premium		79,236		42,770		42,574
		80,508		43,433		43,233

	Number		Number		Number
	(in thousands)
Issued share capital comprises:
Ordinary shares of £0.04 each (2016 and 2015: £0.01    each)		31,811		6,239		6,156
Founder ordinary 1 shares of £0.01 each		—		1,000		1,000
Founder ordinary 2 shares of £0.01 each		—		1,000		1,000
Series A shares of £0.01 each		—		7,483		7,483
Series B shares of £0.001 each		—		8,463		8,463
		31,811		24,185		24,102

Summary of Movement in the Share Capital

11. Share capital and share premium (continued)

	Number of shares		Share capital		Share premium
	(in thousands)
			£		£
Fully paid shares:
Balance at January 1, 2015 and December 31, 2015		24,102		659		42,574
Issue of shares on exercise of options		83		4		196
Balance at December 31, 2016		24,185		663		42,770
Reduction in share premium account		—		—		(42,466	)
Exercise of share options		30		1		119
Bonus issue to series B		—		304		(304	)
Issue of share capital		7,596		304		79,530
IPO costs		—		—		(413	)
Balance at December 31, 2017		31,811		1,272		79,236