| Thomas, A | 0 | U | 192458 | Revenue and Customs |
| Thomas, A | 0 | U | 166562 | Clitheroe |
| Thomas, A | 0 | U | 222450 | Manchester University |
| Thomas, A | 0 | U | 231144 | Thornbury Bristol |
| Thomas, A | 0 | U | 233287 | Norton Radstock |
| Thomas, Aaron | 0 | U | 327599 | Sutton Grammar School |
| Thomas, Aaron Owen | 0 | M | 324850 | Cleveland * |
| Thomas, Adam | 0 | M | 903054 | Middlesex Congresses |
| Thomas, Adam | 0 | M | 342805 | Cheshire & N Wales * |
| Thomas, AI | 0 | U | 120242 | Eastern Knights |
| Thomas, Aimee | 0 | F | 252964 | Oxfordshire Juniors |
| Thomas, Akash | 1685 | M | 345380 | Huddersfield |
| Thomas, Akash | 1636 | U | 345890 | Holmfirth |
| Thomas, Alan | 0 | M | 120243 | Stratford |
| Thomas, Alan | 1375 | M | 143987 | Aigburth |
| Thomas, Alan | 0 | M | 194350 | Barking |
| Thomas, Alastair | 0 | M | 258369 | Kent Junior Congresses |
| Thomas, Alastair | 0 | M | 246092 | Sir Robert Hitchams PS Debenham |
| Thomas, Alex | 1527 | M | 362158 | John Littlewood |
| Thomas, Alex | 0 | U | 309833 | Oxford City |
| Thomas, Alex | 0 | M | 280818 | Reigate St Marys Prep School |
| Thomas, Alexander | 0 | M | 276498 | RA Butler School |
| Thomas, Alice | 0 | F | 258981 | Kensington * |
| Thomas, Amy | 0 | F | 184436 | Penyffordd |
| Thomas, Andrew | 0 | M | 148903 | Bedford Modern School |
| Thomas, Andrew | 0 | M | 257922 | John Fisher School (Surrey) |
| Thomas, Andrew | 0 | U | 258215 | Kent Junior Congresses |
| Thomas, Andrew | 0 | M | 226708 | Wales |
| Thomas, Andrew W | 0 | U | 302311 | Fareham |
| Thomas, Ann | 0 | U | 277712 | Lytham St Annes |
| Thomas, Anne | 0 | F | 273272 | Lytham St Annes |
| Thomas, Anthony | 0 | U | 273531 | Middlesex CCA |
| Thomas, Anthony WR | 0 | M | 120245 | Stroud |
| Thomas, Antos | 0 | M | 324833 | Oxfordshire Juniors |
| Thomas, Arion | 0 | F | 267152 | Coulsdon Chess Club |
| Thomas, Arthur | 0 | U | 317564 | Buckinghamshire* |
| Thomas, Ashley | 0 | M | 259763 | Wales |
| Thomas, Astrid | 0 | F | 346281 | Liverpool * |
