| Name | Region |
|---|---|
| Ortoo Ltd | |
| Orvio | |
| OSCA Digital Ltd | |
| Osca Websites | |
| Oscar Technology | |
| Oscar Temple | |
| osCommerce Templates | Gloucestershire |
| Oscore Ltd | |
| Oscura Ltd | Berkshire |
| Osiris Systems | |
| Osler Diagnostics Ltd | |
| OSS Security | Merseyside |
| OSS Watch | Oxfordshire |
| Ossianix | |
| Ostara Systems Ltd | |
| OstLab | |
| Ostmodern Ltd | |
| OSTTRA Group | |
| OSX Ltd | Wiltshire |
| OTA Insight | |
| Other Media Ltd | |
| Othership | |
| OTHERWORLD | |
| Otimo Partnerships Ltd | |
| Otio | |
| Otrovez Ltd | |
| Ots Labs | |
| Otta Technology Ltd | |
| Our Own | Greater London |
| OurPeople | |
| Out Name is Mud Ltd | |
| Out of Home International | |
| Out of Place Studio | West Yorkshire |
| Outbound Solutions Ltd | |
| Outerbridge Ltd | |
| OuterEdge UK Ltd | West Sussex |
| Outfit7 Ltd | |
| Outlandish Co-Operative | |
| Outlaw web design | Edinburgh |
| Outlier Ventures | |
| Outline Creative | Greater Manchester |
| Outrank | |
| OutReal | Merseyside |
| Outright Games | |
| Outrun Venture Partners, LLP | |
| Outsee Ltd | |
| Outsource Accelerator | |
| Outsource Solutions (NI) Ltd | Antrim and Newtownabbey |
| Outsource2Pak | |
| Outsourced IT Ltd |