| Censornet | |
| CensorNet Ltd | Hampshire |
| Centauri Therapeutics Ltd | |
| Centerprise International | Hampshire |
| Central Networks & Technologies Ltd | Greater Manchester |
| Central One Software Ltd | Derbyshire |
| Central Pharma | |
| Central Technology Belt | |
| Central Technology Ltd | Derbyshire |
| Central Web Services Ltd | Worcestershire |
| Centre Digital | |
| 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 |
| Cerka | |
| Certitec | Swansea |
| Certo Software Ltd | |
| Certum Ltd | Glasgow |
| Certus Technology | |
| Cervest | Greater London |
| Cestrian | Greater Manchester |
| CETA Software Ltd | Oxfordshire |
| Cetix Ltd | Aberdeen |
| Cetronic Power Solutions Ltd | Hertfordshire |
| CEX.IO Ltd | |
| Cezanne HR Ltd | |
| CF Systems | |
| CFH Docmail Ltd | Somerset |
| CFP Ltd | Derbyshire |
| CFP Software Ltd | Cornwall |
| CG Design | Lancashire |
| CG Hero Ltd | |