| Systeme Ouvert Solutions Ltd | Surrey |
| Systemiq Capital | |
| SystemLabs | |
| Systems & Network Training Ltd | Surrey |
| Systems & Solutions | Oxfordshire |
| Systems Engineering & Assessment Ltd | Somerset |
| Systems for Dentists | Tyne and Wear |
| Systems Integration Ltd | |
| Systems IT Support & Consultancy Ltd | |
| Systems Print Media | |
| Systems Valley | |
| systems@work Ltd | |
| SystemsLink 2000 Ltd | |
| SystemWare Europe Ltd | |
| Systemx UK Ltd | |
| Systra Ltd | |
| Sytec | Wiltshire |
| Sytec Computers Ltd | Kent |
| Sytel Ltd | Buckinghamshire |
| Sytemaker.com Ltd | Buckinghamshire |
| T & T Web Design | Ceredigion |
| T A W Consulting | |
| T&H Computer Services Ltd | West Midlands |
| T'Go Creative Ltd | |
| T-Cypher Bio | |
| T-Shomedia | |
| T-Therapeutics | |
| T. Bookman Ltd | South Yorkshire |
| T.O.P. SEO | |
| T2 Labs Pte Ltd | |
| T34 | Merseyside |
| Tabard IT Ltd | Edinburgh |
| TableFlip Ltd | |
| TAC Design Ltd | Tyne and Wear |
| Tachodisc Distribution UK Ltd | Kent |
| Tachograph Analysis Consultants Ltd | |
| Tactful Ltd | |
| Tactile Solutions | |
| Tactuum | |
| TAD360 | |
| TAG Company UK | Greater London |
| TAG Consultants Ltd | |
| Tag Games Ltd | Dundee |
| TAG International | |
| Taggr Ltd | |
| Tagomics Ltd | |
| Tagtronics Ltd | Lancashire |
| Tagz | Greater Manchester |
| Tahninial | South Yorkshire |
| Tailify | |