| Carmen Data Ltd | |
| Carn Software Ltd | North Lanarkshire |
| Carnaby West | |
| Carnedd | |
| Carnival Digital Graphics | Somerset |
| Caro Creative | |
| Caroline Hagan Consultancy | |
| Carousel Projects | |
| carputer-shop.co.uk | Leicestershire |
| Carrick Creative | |
| Carrick Web Design | |
| Carrot.co.uk Ltd | Hertfordshire |
| Carswell Gould | |
| Cart-Power, LLP | |
| Carter Voce Security Ltd | Hertfordshire |
| Cartoozo | |
| Cartridge Discount | Northumberland |
| Cartridge Express | West Yorkshire |
| Cartridge People Ltd | |
| Cartridge Save Ltd | Greater Manchester |
| Cartridge Shop (UK) Ltd | Staffordshire |
| Cartridge World | |
| CartridgeMonkey | Greater Manchester |
| Cartwright IT Consultants | |
| CASE Medicine | |
| Casestyle | |
| Cash Processing Solutions | Hampshire |
| Cashew Fintech Ltd | |
| Cashflows | Cambridgeshire |
| Cashmaster International Ltd | Fife |
| Cashoff | |
| Casino Marketing Agency | |
| Caspa Technologies Ltd | |
| Caspia Consultancy | |
| Caspian Blue Ltd | Hertfordshire |
| Casque SNR | Lancashire |
| Cassava Technologies | |
| Cassini Systems | |
| Cassini.tech | |
| Castle Computers Ltd | Berkshire |
| Castle International Ltd | |
| Castle Microwave Ltd | Berkshire |
| Castlegate IT Ltd | North Yorkshire |
| Castline Systems | West Sussex |
| Castus Ltd | |
| Catalis, L.P. | |
| Catalysoft Ltd | Essex |
| Catalyst | |
| Catalyst Internet Consultancy Ltd | Isle of Wight |
| CATalyst Systems | Denbighshire |