| Nybble.co.uk Ltd | Lancashire |
| Nyble Ltd | |
| Nymbl | |
| NYnet | |
| Nyobolt | |
| Nyota AI Ltd | |
| Nyquist Solutions Ltd | Wiltshire |
| Nzime Ltd | |
| O'Connor Web Design | |
| O-Zone Technologies Ltd | |
| o2h Group | |
| o2h Technology | |
| O2Soft | |
| Oak Hill Bio Ltd | |
| Oak Software Ltd | Leicestershire |
| OAK Telecom Ltd | Dorset |
| Oak Tree Management & Training Ltd | Suffolk |
| Oakley Wilkinson Bryan Ltd | |
| OakNorth Credit Intelligence | |
| Oakwood Computing Associates Ltd | Greater London |
| Oasis Consultation Ltd | |
| Oasis Ltd | |
| Oasys Software | |
| Oasys Technologies Ltd | |
| Oathello | |
| Oban International | |
| Obergine | Oxfordshire |
| ObjectDB Software Ltd | Nottinghamshire |
| Objective 1 Ltd | |
| Objective Associates | Stirling |
| Objective Computing Ltd | Essex |
| Objective Imaging Ltd | Cambridgeshire |
| Objectivity Ltd | West Midlands |
| Objectsource | |
| Objectverse Ltd | |
| Oblongata Ltd | |
| Obrela | |
| Obrizum Group Ltd | |
| Obviously Group Ltd | |
| OC&C Strategy Consultants, LLP | |
| Ocado Technology | |
| OCC Computer Personnel | Cheshire |
| Occam | |
| Ocean Blue Software | |
| Ocean Blue Software Ltd | Bristol |
| Ocean Power Ltd | |
| Ocean Signal Ltd | |
| Ocean Technologies Group | |
| Ocean Telecom | Suffolk |
| Ocean View Games | |