| Oxford Vacmedix | |
| Oxford Vacmedix UK Ltd | |
| Oxford Valuation Partners | |
| Oxford Vision & Sensor Technology | West Midlands |
| OxfordQuantumCircuits | |
| Oxgene | |
| Oxinet | Oxfordshire |
| Oxon IT Support | |
| Oxular | |
| Oxwash | |
| Oxx | Greater London |
| Oxygen Elements | |
| Oxygen Finance | |
| Oxyrane | |
| Oyster Marketing & Design | Hampshire |
| OZ-UK Ltd | |
| P&L Networks | Cheshire |
| P&Q International plc | |
| P+M Services (R) Ltd | West Yorkshire |
| P11D Organiser | Greater Manchester |
| P1vital Ltd | |
| P2 Technologies | |
| P2i Ltd | Oxfordshire |
| P3 Computer Services Ltd | Lancashire |
| P4B Digital Agency | |
| PA Consulting | |
| PAB Studios Ltd | |
| PAC Software Ltd | |
| PAC Web Hosting Ltd | |
| PAC Webhosting Ltd | Cheshire |
| PACE Software Development Ltd | South Yorkshire |
| Pace Telecom | Wrexham County Borough |
| Paced Email | |
| Pacetech.com | |
| Pacific Infotech (UK) Ltd | Greater London |
| Packet Ship Technologies Ltd | Cornwall |
| Packnet Ltd | Greater Manchester |
| Packt | West Midlands |
| Pactio Technologies Ltd | |
| Pad Creative Ltd | |
| Paddle.com Market Ltd | |
| Padua Communications Ltd | |
| Page Creative | |
| Page Flows | |
| Page Hosting | Hampshire |
| Pagefield | |
| Pagepro Ltd | |
| Pagers Direct | Northamptonshire |
| PageSuite Ltd | |
| Pageworks Ltd | West Midlands |