| Capital Refractories Ltd | |
| Capital Training | West Sussex |
| Capitalgram | |
| Capitalise.com Platform Ltd | |
| Capito Ltd | West Lothian |
| Cappfinity | |
| Capri Healthcare Ltd | |
| CAPSLOCK | |
| Caption Data | |
| Carat | |
| Carbometrics Ltd | |
| Carbon Clean | |
| Carbon Cloud Ltd | |
| Carbon Creative | |
| Carbon Digital | |
| Carbon Six Digital | Surrey |
| Carbon13 | |
| CarbonChain | |
| Carbonplace | |
| Carcinotech | |
| Carcinotech Ltd | |
| CardiaTec Biosciences | |
| CardiaTec Biosciences Ltd | |
| Cardiff Computers | |
| Cardiff Media | |
| Cardiff Metropolitan University | Cardiff |
| Cardiff University | Cardiff |
| Cardiff University - School of Computer Science and Informatics | Cardiff |
| Cardiff University - School of Mathematics | Cardiff |
| Cardiff Web Development | |
| Cardiff Web Services | |
| Cardinal IT Ltd | Edinburgh |
| CardioPrecision Ltd | |
| Cardonet | |
| Care Computers and Services Ltd | Berkshire |
| Care Control Systems | |
| Care Software Solutions Ltd | |
| CareTeam | |
| Caretech Systems Ltd | Northumberland |
| Caretower | Greater London |
| Caretta Software Ltd | Oxfordshire |
| Cargo Creative Ltd | |
| Cargo Stream | |
| Cargo Technologies Ltd | |
| Cariad Marketing Ltd | |
| Cariboo Digital | |
| Caricaturer.io | |
| Caristo Diagnostics | Oxfordshire |
| Carlton Danutson | Wrexham County Borough |
| Carlton Training Ltd | |