| Thisworks Advertising & Marketing Ltd | Cheshire |
| Thomas Bloom | |
| Thomas Cole Search | |
| Thomas Neil | Glasgow |
| Thompson Group | |
| Thorn SDS | Hampshire |
| Thornber Employment Law Ltd | |
| Thornton & Ross | |
| Thorogood Software | Lincolnshire |
| Thought Collective | |
| Thought Consultancy Ltd | Tyne and Wear |
| Thought Machine | Greater London |
| Thought Machine Group Ltd | |
| Thought&Function | |
| ThoughtRiver | |
| ThoughtShift Ltd | |
| ThouVis Software Ltd | West Midlands |
| Threadgold Consulting | |
| Thredd Group Ltd | |
| Three Cherries Ltd | Bristol |
| Three Circle | |
| Three Hills | |
| Three One Zero Design Ltd | |
| Three Part Story | |
| THREE60 Energy | |
| threebit Studio Ltd | Leicestershire |
| Threedium | |
| Threeguru | |
| threesixfive DGTL Ltd | |
| Thriva Ltd | |
| Thrive | |
| Thrive Marketing Ltd | |
| Thrive Renewables plc | |
| Thrive.App Ltd | Belfast |
| ThriveMap Ltd | Greater London |
| Thrombosis Research Institute | |
| Throneware Ltd | |
| Thuk | Bedfordshire |
| Thule Media | |
| Thumbmunkeys | |
| Thunderbolt Digital | Surrey |
| Thunderwerx Ltd | |
| Thurrock PC Services | Essex |
| Thursday Studio | |
| Thyme Marketing | |
| Thyngs | |
| TH_NK | Greater London |
| Tibor Darvas Ltd | Buckinghamshire |
| Tibus | Ards and North Down |
| Tickbox Marketing | Bristol |