| Share-based compensation (Tables)
 | 12 Months Ended | 
| Dec. 31, 2024 | 
|---|
| Share-based compensation |  | 
| Schedule of options granted to non-executive directors under the Adaptimmune Therapeutics plc 2015 Share Option Scheme | Generally, the vesting dates for the options granted under these plans up to December 31, 2024 are 25% on the first anniversary of the grant date and 75% in monthly installments over the following three years. However, the options  granted to non-executive directors under the Adaptimmune Therapeutics plc 2015 Share Option Scheme vest and become exercisable as follows: 
|  |  |  |  
|  |  |  |  
| Options granted to non-executive directors on May 11, 2015: |      | Immediately on grant date |  
| Options granted to a non-executive director on June 23, 2016: |  | 25% on the first anniversary of the grant date and 75% in monthly installments over the following two years |  
| Options granted to non-executive directors on August 11, 2016: |   | 100% on the first anniversary of the grant date  |  
| Options granted to non-executive directors on November 28, 2016: |   | 25% on the first anniversary of the grant date and 75% in monthly installments over the following two years |  
| Options granted to non-executive directors on July 3, 2017 |  | 100% on the first anniversary of the grant date |  
| Options granted to non-executive directors on June 22, 2018: |  | 100% on the first anniversary of the grant date |  
| Options granted to a non-executive director on July 5, 2018: |  | 25% on the first anniversary of the grant date and 75% in monthly instalments over the following two years |  
| Options granted to non-executive directors on July 2, 2019: |  | 100% on the first anniversary of the grant date |  
| Options granted to non-executive directors on July 1, 2020: |  | 100% on the first anniversary of the grant date |  
| Options granted to non-executive directors on July 1, 2021: |  | 100% on the first anniversary of the grant date |  
| Options granted to non-executive directors on July 1, 2022: |  | 100% on the first anniversary of the grant date |  
| Options granted to non-executive directors on July 3, 2023: |  | 100% on the first anniversary of the grant date |  
| Options granted to a non-executive director on November 1, 2023: |  | 25% on the first anniversary of the grant date and 75% in monthly instalments over the following two years |  
| Options granted to non-executive directors on January 15, 2024: |  | 100% on the first anniversary of the grant date |  
| Options granted to non-executive directors on July 1, 2024: |  | 100% on the first anniversary of the grant date |  | 
| Summary of share-based compensation expense included in the consolidated statements of operations | The following table shows the total share-based compensation expense included in the Consolidated Statements of Operations (in thousands): 
|  |  |  |  |  |  |  |  |  |  |  
|  |  | Year ended  |  | Year ended  |  | Year ended |  
|  |  | December 31,  |  | December 31,  |  | December 31,  |  
|  |  | 2024 |      | 2023 |      | 2022 |  
| Research and development |  | $ |  3,875 |  | $ |  3,061 |  | $ |  6,264 |  
| Selling, general and administrative |  |   |  8,176 |  |   |  8,712 |  |   |  11,976 |  
|  |  | $ |  12,051 |  | $ |  11,773 |  | $ |  18,240 |  | 
| Summary of information about share options granted | 
|  |  |  |  |  |  |  |  |  |  |  
|  |  | Year ended  |  
|  |  | December 31,  |  
|  |  |  | 2024 |      | 2023 |  | 2022 |  
| Number of options over ordinary shares granted |  |  | 55,282,716 |  |  | 60,891,430 |  |  | 31,826,293 |  
| Weighted average fair value of ordinary shares options |  | $ | 0.12 |  | $ | 0.12 |  | $ | 0.37 |  
| Number of additional options with a nominal exercise price granted |  |  | 34,560,096 |  |  | 27,375,252 |  |  | 24,248,424 |  
| Weighted average fair value of options with a nominal exercise price  |  | $ | 0.15 |  | $ | 0.27 |  | $ | 0.51 |  | 
| Summary of all stock option activity |  The following table summarizes all stock option activity for the year ended December 31, 2024:  
|  |  |  |  |  |  |  |  |  |  |  |  
|  |      |  |      |  |      |  |      |  |  |  
|  |  |  |  | Weighted |  | Average |  |  |  
|  |  |  |  | average |  | remaining |  | Aggregate |  
|  |  |  |  | exercise price |  | contractual |  | intrinsic value |  
|  |  | Options |  | per option |  | term (years) |  | (thousands) |  
| Outstanding at January 1, 2024 |   |  191,150,175 |  | £ |  0.41 |  |  |  |  |  |  
| Changes during the period: |  |  |  |  |  |  |  |  |  |  |  
| Granted |   |  89,842,812 |  | £ |  0.08 |  |  |  |  |  |  
| Exercised |  |  (8,976,462) |  | £ |  0.01 |  |  |  |  |  |  
| Expired |  |  (14,454,205) |  | £ |  0.52 |  |  |  |  |  |  
| Forfeited |   |  (4,175,144) |  | £ |  0.07 |  |  |  |  |  |  
| Outstanding at December 31, 2024 |   |  253,387,176 |  | £ |  0.31 |   |  6.9 |  | £ |  4,698 |  
| Exercisable at December 31, 2024 |   |  129,110,391 |  | £ |  0.50 |   |  5.1 |  | £ |  873 |  | 
| Summarizes information about stock options granted based on the market value at grant date which were outstanding | The following table summarizes information about stock options granted based on the market value at grant date which were outstanding as of December 31, 2024: 
|  |  |  |  |  |  |  |  |  |  |  |  
|  |  |  |  | Weighted |  | Average |  |  |  |  
|  |  |  |  | average |  | remaining |  | Aggregate |  
|  |  |  |  | exercise price |  | contractual |  | intrinsic value |  
|  |      | Options |      | per option |      | term (years) |      | (thousands) |  
| Outstanding at January 1, 2024 |   |  147,670,115 |  | £ |  0.53 |  |  |  |  |  131 |  
| Changes during the period: |  |  |  |  |  |  |  |  |  |  |  
| Granted |   |  55,282,716 |  | £ |  0.12 |  |  |  |  |  |  
| Exercised |  |  (622,278) |  | £ |  0.09 |  |  |  |  |  |  
| Expired |  |  (14,378,110) |  | £ |  0.53 |  |  |  |  |  |  
| Forfeited |   |  (1,098,173) |  | £ |  0.27 |  |  |  |  |  |  
| Outstanding at December 31, 2024 |   |  186,854,270 |  | £ |  0.41 |   |  6.4 |  | £ |  4 |  
| Exercisable at December 31, 2024 |   |  116,768,430 |  | £ |  0.49 |   |  5.0 |  | £ |  2 |  | 
| Summary of information about RSU-style options which are outstanding | The following table summarizes information about RSU-style options which were outstanding as of December 31, 2024: 
|  |  |  |  |  |  |  |  |  |  
|  |  |  |  |  | Average |  |  |  |  
|  |  |  |  |  | remaining |  | Aggregate |  
|  |  |  |  |  | contractual |  | intrinsic value |  
|  |      | Options |      |  | term (years) |      | (thousands) |  
| Outstanding at January 1, 2024 |   |  43,480,060 |  |  |  8.1 |  |  |  4,470 |  
| Changes during the period: |  |  |  |  |  |  |  |  |  
| Granted |   |  34,560,096 |  |  |  |  |  |  |  
| Exercised |  |  (8,354,184) |  |  |  |  |  |  |  
| Expired |  |  (76,095) |  |  |  |  |  |  |  
| Forfeited |   |  (3,076,971) |  |  |  |  |  |  |  
| Outstanding at December 31, 2024 |   |  66,532,906 |  |  |  8.1 |   | £ |  4,695 |  
| Exercisable at December 31, 2024 |   |  12,341,961 |  |  |  6.1 |   | £ |  871 |  | 
| Summary of information about stock options outstanding |  
|  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
| Outstanding |  | Exercisable |  
|  |  |  |  |  | Weighted- |  |  |  |  |  |  |  |  |  
|  |  |  |  |  | average |  | Weighted- |  |  |  | Weighted- |  
|  |  |  | Total share |  | remaining |  | average |  | Total share |  | average |  
| Exercise price |      | options |      | contractual life |      | exercise price |      | options |      | exercise price |  
| £ | 0.001 |      |  66,532,906 |  |  8.1 |      | £ |  0.00 |  |  12,341,961 |      | £ |  0.00 |  
|  | 0.01 - 0.25 |  |  74,588,395 |  |  8.5 |  |  |  0.13 |  |  19,963,611 |  |  |  0.15 |  
|  | 0.26 - 0.50 |   |  48,832,463 |  |  6.6 |   |  |  0.37 |  |  34,325,165 |   |  |  0.39 |  
|  | 0.51 - 0.75 |   |  35,763,545 |  |  3.6 |   |  |  0.59 |  |  35,390,721 |   |  |  0.59 |  
|  | 0.76 - 1.00 |   |  21,844,478 |  |  4.0 |   |  |  0.84 |  |  21,549,378 |   |  |  0.84 |  
|  | 1.01 - 1.50 |   |  3,311,907 |  |  4.4 |   |  |  1.30 |  |  3,274,431 |   |  |  1.30 |  
|  | 1.51 - 2.00 |   |  1,879,690 |  |  4.3 |   |  |  1.67 |  |  1,719,718 |   |  |  1.67 |  
|  | Over 2.00 |   |  633,792 |  |  6.0 |   |  |  4.30 |  |  545,406 |   |  |  4.47 |  
| Total |   |  253,387,176 |   |  6.9 |   | £ |  0.31 |   |  129,110,391 |   | £ |  0.50 |  | 
| Summary of the assumptions used to estimate the fair values of the share options granted using the Black-Scholes option-pricing model |  
|  |  |  |  |  |  |  |  
|  |  | Year ended  |  | Year ended  |  | Year ended  |  
|  |  | December 31,  |  | December 31,  |  | December 31,  |  
|  |      | 2024 |      | 2023 |      | 2022 |  
| Expected term |   | 5 years |   | 5 years |   | 5 years |  
| Expected term (TCR2 replacement options) |  |  — |  | 0.5 - 4 years |  |  — |  
| Expected volatility |  | 104-105% |  | 84-113% |  | 99-101% |  
| Risk free rate |   | 3.55-3.99% |   | 3.27-4.52% |   | 0.94-3.90% |  
| Expected dividend yield |  | 0% |  | 0% |  | 0% |  |