| UKspace | |
| Uleska Ltd | |
| Ulster University | Belfast |
| Ulster University - School of Computing | Belfast |
| Ultima Business Solutions Ltd | Berkshire |
| Ultimate Communication Software Ltd | |
| Ultimate Finance | |
| Ultimate Website Design | Essex |
| Ultimateweb Ltd | Leicestershire |
| Ultimedia Systems Ltd | Derbyshire |
| UltimVR | |
| Ultra Global | |
| Ultraleap Ltd | |
| UltraSoft Technologies Ltd | |
| Ultrasonic Sciences Ltd | Hampshire |
| Ultratec Ltd | Hertfordshire |
| Ultromics Ltd | |
| Umami | Merseyside |
| Umazi Ltd | |
| UmbHost Ltd | |
| Umbrella Analytics Ltd | |
| Umi Digital | |
| Umlaut | |
| UMM Digital | Greater London |
| uMotif Ltd | |
| Unbound Innovations Ltd | |
| Unboxed | |
| Unbranded Digital | West Yorkshire |
| UNBXD | |
| Uncapped Ltd | |
| Uncovered Design Studio | |
| Uncrowd | |
| Undaunted | |
| Under One Cloud | |
| Underscore | |
| Underwaterpistol Ltd | |
| Undo | Cambridgeshire |
| Unecom | Leicestershire |
| Uni-Mail Ltd | Oxfordshire |
| Unibuddy | |
| Unicom Communications | |
| Unicorn Biotechnologies | |
| Unicorn Designers | Suffolk |
| Unicsoft | |
| Unified | |
| Unified Business Systems Ltd | Nottinghamshire |
| Unified Software | Tyne and Wear |
| Unified World Communications | Lancashire |
| Unify AI Ltd | |
| Unilever Ventures | |