| TheGamery Ltd | |
| Thema AI Ltd | |
| Themepaste | |
| Theodo | |
| Theolytics | |
| Theorem Solutions | Staffordshire |
| TheraCryf plc | |
| Theragnostics Ltd | |
| Therakind | |
| Theramex | |
| Therapy Webs | Staffordshire |
| Thermeon Ltd | |
| Thermocable (Flexible Elements) Ltd | West Yorkshire |
| Theta Trading Systems Ltd | |
| TheTin | Greater London |
| TheWaay | |
| TheWebsiteGroup | Hertfordshire |
| TheWebSmiths | Cheshire |
| THG plc | |
| Thin Martian | |
| ThingCo Ltd | |
| Thingy Club | |
| Think 4wd | Merseyside |
| Think Creative Consultants Ltd | |
| Think Digitally | |
| Think Direct | |
| Think Little Big Marketing Ltd | |
| Think3 | |
| ThinkAnalytics Ltd | |
| ThinkBDW | |
| ThinkEQ | |
| Thinking Computers | West Yorkshire |
| Thinklab | |
| Thinkle Company Ltd | |
| Thinkpad Creative | Tyne and Wear |
| ThinkTank Maths Ltd | Edinburgh |
| Thintech Ltd | |
| Third Dimension Ltd | Dorset |
| Third Financial Software Ltd | |
| Third Light Ltd | Cambridgeshire |
| Third Platform Technologies | |
| Thirdfort Ltd | |
| ThirtyFiveBio | |
| THIS | |
| This Is Chemistry Ltd | |
| This is Embrace Ltd | |
| This Is Fever Ltd | |
| This is Needle Ltd | |
| This Way Up | |
| Thisdotsoftware | |