| Name | Region |
|---|---|
| Ōgi Bio | |
| OgiBio | |
| Ogier | |
| OGL Computer | Worcestershire |
| OH Digital | |
| Oh Tech | |
| Ohana Studio Ltd | |
| OHC Ltd | |
| OhSo Technical Ltd | Greater London |
| OI Media Ltd | Gloucestershire |
| OKKO Health | |
| OKM Solutions | |
| OKO Digital | Hampshire |
| OKRA Technologies | Cambridgeshire |
| OKSO Ltd | Dorset |
| OKW Enclosures Ltd | Hampshire |
| OKYO Pharma Ltd | |
| Old St Labs | |
| Oleg Andreev | |
| OlexSys Ltd | |
| Olio | Greater London |
| Oliver Jackson | Edinburgh |
| OLS | |
| Olson Applications Ltd | |
| Olympic Ltd | Dorset |
| Olympus Automation | Cambridgeshire |
| Ombush Media Ltd | |
| OMC Medical | |
| OMdeSIGN Digital Agency | |
| Omecu | Glasgow |
| Omecu Ltd | |
| Omeg Ltd | West Sussex |
| Omega Diagnostics Group plc | |
| Ometria Ltd | |
| Omideon Ltd | |
| Omiga Technology Ltd | Gloucestershire |
| Omnea | |
| Omnevue | |
| Omni Search Digital | |
| Omnio Global | |
| Omnipresent Group | |
| Omnis Software Ltd | Suffolk |
| Omnis Systems | East Sussex |
| Omnisity Ltd | |
| Omnius Partners Ltd | |
| Omniweb Ltd | Surrey |
| OMNIX Software Solutions Ltd | West Midlands |
| Omron Electronics Ltd | Buckinghamshire |
| OMS Digital Marketing | |
| Omtech Masters Ltd |