| Line Item | Dec 31, 2025 | Dec 31, 2024 | Dec 31, 2023 | Dec 31, 2022 | Dec 31, 2021 | Dec 31, 2020 | Dec 31, 2019 | Dec 31, 2018 | Dec 31, 2017 |
|---|---|---|---|---|---|---|---|---|---|
| Profit or loss [abstract] | |||||||||
| Revenue | |||||||||
| Costs of services | |||||||||
| Gross profit | |||||||||
| General and administrative costs | |||||||||
| Operating profit | |||||||||
| Earnings from associates | |||||||||
| Profit before interest and taxation | |||||||||
| Finance and investment income | |||||||||
| Finance costs | |||||||||
| Revaluation and retranslation of financial instruments | |||||||||
| Profit before taxation | |||||||||
| Taxation | |||||||||
| (Loss)/profit for the year | |||||||||
| Attributable to: | |||||||||
| Equity holders of the parent | |||||||||
| Non-controlling interests | |||||||||
| (Loss)/profit for the year | |||||||||
| Earnings per share | |||||||||
| Basic earnings per ordinary share (sterling per share) | |||||||||
| Diluted earnings per ordinary share (sterling per share) |