| Seda Pharmaceutical Development Services | |
| Sedao Digital Signage | Kent |
| Sedgewall Ltd | Bedfordshire |
| SEDNA Communications Ltd | |
| Seeai | |
| SeeByte Ltd | |
| SeeChange Technologies Ltd | |
| Seed Enterprise Investment Scheme | |
| SEED Marketing Communications | |
| Seedance | |
| seeDATA Ltd | |
| Seedata.IO Ltd | |
| Seedcamp | Greater London |
| Seedcloud | |
| Seedr Creative Ltd | |
| Seedrs Ltd | Greater London |
| SEEDTECH Studios Ltd | |
| Seek Social Ltd | |
| Seeker Digital | Bristol |
| Seemore Graphics Ltd | Hampshire |
| Seen | Norfolk |
| Seenit Digital Ltd | |
| Seer | |
| Seer Computing Ltd | Swansea |
| Seetrax CAE Ltd | Hampshire |
| SEG Communications | Hertfordshire |
| Segmentify | |
| SegmentStream | Greater London |
| Seiki Systems | East Sussex |
| Seiretto | West Yorkshire |
| Seismic Technology Ltd | Suffolk |
| Selcia Ltd | |
| Selcom Systems Ltd | North Yorkshire |
| Seldon Technologies Ltd | Greater London |
| Select Legal Systems Ltd | East Riding of Yorkshire |
| Select Performers Internet Solutions | Greater Manchester |
| Select Sourcing | West Midlands |
| Select Technology Ltd | Hampshire |
| Select Web Design | South Lanarkshire |
| Selectbase Ltd | Kent |
| Selesti | |
| Selftalk | |
| Sell My Old Mobile Phone | |
| Sellar | |
| Sellec Ltd | Nottinghamshire |
| Sellerdeck | |
| SellerX | |
| Sellick Partnership | |
| SellMyCellPhones.com | Warwickshire |
| Sellr | |