| Sixfold Bioscience | |
| Sixth Level Marketing Ltd | Hampshire |
| Sixth Sense Consulting | |
| Sixth Sense Training | South Lanarkshire |
| Siya Tech Ventures | |
| SJ Communications Ltd | Nottinghamshire |
| SJ Electronics | Northamptonshire |
| SJD Computers Ltd | Lincolnshire |
| SJI Design | Buckinghamshire |
| SJL Web Design | |
| Sjones.digital | |
| SK Electronics | Greater Manchester |
| SK Pang Electronics Ltd | Essex |
| SK Web World | |
| Skill Beyond Boundaries Ltd | |
| Skill Drill Learning Ltd | |
| Skill Search Computing Ltd | East Sussex |
| Skill-IS Ltd | East Sussex |
| Skillbank | Tyne and Wear |
| Skiller Whale | |
| SkillRecruit | |
| Skills Development Scotland | |
| SkillsGen | Merseyside |
| Skillwork Software and Consulting Ltd | |
| Skimlinks | |
| Skin Analytics | |
| SkinBioTherapeutics plc | |
| Skipso | |
| SKNUPS | |
| Skocia Web Design | Glasgow |
| Skrill Ltd | |
| Skriply | |
| SKSServices.co.uk | Essex |
| Skweeze Ltd | |
| Sky Engine AI | |
| Sky International AG | Hertfordshire |
| Sky Potential Technologies | |
| Skya Designs | |
| SkyDemon | Somerset |
| Skylark Control Ltd | |
| Skylark Lasers Ltd | |
| Skylight Media Ltd | Essex |
| Skyline Internet Ltd | Lincolnshire |
| Skyline Wireless Ltd | |
| Skylock Ltd | Nottinghamshire |
| Skynet | Northamptonshire |
| Skynet Applied Systems Ltd | |
| Skyrocket Your Search | |
| Skyron Ltd | |
| Skyrora Ltd | |