Share-based payments - Significant inputs into the model & Fair Value (Details)	12 Months Ended
Dec. 31, 2023 GBP (£) Y £ / shares	Dec. 31, 2022 GBP (£) Y £ / shares
Share-based payments
Fair value of awards granted \| £	£ 36,000,000	£ 19,000,000
Weighted average fair value per award granted \| £	£ 5.067	£ 3.859
Weighted average share price for options exercised	£ 5.686	£ 4.999
Weighted average contract term remaining on shares unexercised	497 days	527 days
Performance Shares
Share-based payments
Share price	£ 5.814	£ 4.805
Expected share price volatility, percentage	26.30%	23.90%
Median share price correlation between the companies in the comparator group, percentage	84.10%	84.00%
Expected life \| Y	3	3
Exercise price of the nil-cost awards	£ 0	£ 0

The expected volatility of the share price used to calculate the fair value of the share options granted. Expected volatility is a measure of the amount by which a price is expected to fluctuate during a period. The measure of volatility used in option pricing models is the annualised standard deviation of the continuously compounded rates of return on the share over a period of time.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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The option life of share options granted.

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Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with members defined in one or many axes of the table.

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The exercise price of share options granted.

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The weighted average share price at the date of exercise for share options that are exercised in a share-based payment arrangement. [Refer: Share-based payment arrangements [member]; Weighted average [member]]

+ References

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The weighted average fair value of share options granted during the period at the measurement date. [Refer: Weighted average [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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The weighted average remaining contractual life of outstanding share options. [Refer: Weighted average [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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The weighted average share price used as input to the option pricing model to calculate the fair value of share options granted. [Refer: Option pricing model [member]; Weighted average [member]]

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The median share price correlation between the companies in the comparator group used to calculate the fair value of the share options granted.

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Fair value of share options granted under the share-based payment arrangement.

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