| Celentyx | |
| Celestial | Greater London |
| Cell Pack Solutions | Tyne and Wear |
| Cell ProTx Ltd | |
| Cell Software | |
| CellCentric Ltd | |
| Cellesce Ltd | |
| Cellexus | |
| Cellhire plc | North Yorkshire |
| Cellomatics BioSciences Ltd | |
| CellPoint Digital | |
| Cellular Origins Ltd | |
| Cellular Solutions Ltd | Tyne and Wear |
| Cellular Therapeutics Ltd | |
| CeloApps | |
| Celtic Renewables | |
| CEM Systems | Belfast |
| Cemoc Ltd | Isle of Wight |
| CENSIS | |
| Censornet | |
| CensorNet Ltd | Hampshire |
| Centauri Therapeutics Ltd | |
| Centerprise International | Hampshire |
| Central Networks & Technologies Ltd | Greater Manchester |
| Central One Software Ltd | Derbyshire |
| Central Technology Belt | |
| Central Technology Ltd | Derbyshire |
| Central Web Services Ltd | Worcestershire |
| Centre for Engineering Education & Development | Glasgow |
| Centrepoint Computer Services Ltd | |
| CentreSoft Ltd | West Midlands |
| Centrex Services | |
| Centric Web Solutions Ltd | |
| Centrica plc | |
| Centriq Ltd | Greater London |
| Centurian.net | Wiltshire |
| Century IT Services | |
| Century Software Ltd | |
| Century Web Design | Cardiff |
| Century-Tech Ltd | Greater London |
| Ceol Mor Software & Publishing Ltd | Highland |
| Cephos Electronic Circuits Ltd | Kent |
| Cepro Communications | |
| Ceratech Accuratus Ltd | Hampshire |
| Cerbos | Greater London |
| Cerebral Agency Ltd | |
| CereProc Ltd | Edinburgh |
| Ceres | |
| Ceri Williams | Cardiff |
| Certitec | Swansea |