| Collaborative Connections | West Sussex |
| Collate Business Systems Ltd | Hampshire |
| Collctiv Ltd | |
| Colleague Software Ltd | Norfolk |
| Colleges Scotland | |
| Collegia | |
| Collidr Technologies Ltd | |
| Collision Management Systems Ltd | |
| Colmworth Electronics Ltd | Cambridgeshire |
| Colorintech | |
| Colortrac Ltd | Cambridgeshire |
| Colt Technology Services Group Ltd | |
| Columbus Telecom Ltd | Glasgow |
| Colva Ltd | |
| Colvill Banks Ltd | Hampshire |
| Colza | Greater London |
| Com5 | Hampshire |
| Combine Studio | South Yorkshire |
| Combine.ai | |
| Comcare Technology Ltd | Cheshire |
| Comcen Computer Supplies Ltd | Swansea |
| Comfort Click Ltd | |
| Comgem Ltd | Bridgend |
| Comgen | Bedfordshire |
| Comino Holding Ltd | |
| Comloc Computer Security | Greater Manchester |
| Comm Store Ltd | Norfolk |
| Comm-Tech | |
| Comm-Tech Martham Ltd | Norfolk |
| Comma Payments Ltd | |
| CommAgility Ltd | Leicestershire |
| Commatic | Gloucestershire |
| Commerce Centric | Berkshire |
| CommerceTuned | Hertfordshire |
| Commercial Ltd | Gloucestershire |
| Commerzbank AG London Branch | |
| Commissum | Edinburgh |
| Commlinks | Greater London |
| Common Ground | Oxfordshire |
| Common Knowledge | |
| Common VC | Greater London |
| Commonplace | |
| Commonwealth Telecommunications Organisation | Greater London |
| Comms Consultants | Cheshire |
| Comms Express Ltd | Essex |
| Comms Group (UK) Ltd | Northamptonshire |
| Comms.UK Ltd | Dorset |
| CommsFM Ltd | Glasgow |
| Commsplus Ltd | Somerset |
| Commsupport Networks Ltd | |