| Ten-25 Software Ltd | Dorset |
| Ten10 | |
| Tenacity Works | |
| Tendable | |
| Tended | |
| Teneo Ltd | Berkshire |
| Tenkay Electronics Ltd | West Sussex |
| Tenpoint Therapeutics Ltd | |
| Tensor plc | Cambridgeshire |
| Tentacle Computers | Suffolk |
| Tentacle Solutions Ltd | Glasgow |
| Tentamus Pharma (UK) Ltd | |
| Tenyks | |
| Tenzo | Greater London |
| Tepnel Pharma Services Ltd | |
| Teque | |
| TeraByte IT Ltd | County Durham |
| Teranode | |
| Teratech Components Ltd | |
| TeraView Ltd | |
| Terinea | East Sussex |
| Ternary Therapeutics Ltd | |
| Terra | |
| Terracoding | South Yorkshire |
| TerraPay Holdings Ltd | |
| Terrier SC Ltd | Kent |
| Terrington Data Management | North Yorkshire |
| TES Group | Lancashire |
| Tessella | Oxfordshire |
| Tessellate Design Studio | |
| Tessl AI Ltd | |
| Test Driven Solutions | |
| Test Equipment Solutions Ltd | Berkshire |
| Test Management Systems Ltd | Buckinghamshire |
| Testdome | |
| Testhouse | Greater London |
| Testing Performance | |
| TESTQ Technologies Ltd | |
| testscenario | Greater London |
| Testwall Ltd | Edinburgh |
| TETRA and Critical Communications Association | Tyne and Wear |
| Tetra Interactive | Derbyshire |
| Tetra Tech | |
| Tetra Technology Ltd | |
| Tetrabyte Ltd | |
| Tetrad Discovery Ltd | |
| Tewktech Ltd | Gloucestershire |
| Texcel Technology plc | Greater London |
| Texecom Ltd | Lancashire |
| Texel Ltd | Greater London |