| carputer-shop.co.uk | Leicestershire |
| Carrick Web Design | |
| Carrot.co.uk Ltd | Hertfordshire |
| Carter Voce Security Ltd | Hertfordshire |
| Cartridge Discount | Northumberland |
| Cartridge Express | West Yorkshire |
| Cartridge People Ltd | |
| Cartridge Save Ltd | Greater Manchester |
| Cartridge Shop (UK) Ltd | |
| Cartridge World | |
| CartridgeMonkey | Greater Manchester |
| Cartwright IT Consultants | |
| Casestyle | |
| Cash Processing Solutions | Hampshire |
| Cashew Fintech Ltd | |
| Cashflows | Cambridgeshire |
| Cashmaster International Ltd | Fife |
| Cashoff | |
| Caspia Consultancy | |
| Caspian Blue Ltd | Hertfordshire |
| Casque SNR | Lancashire |
| Cassava Technologies | |
| Cassini Systems | |
| Cassini Systems | |
| Cassini.tech | |
| Castle Computers Ltd | Berkshire |
| Castle International Ltd | |
| Castle Microwave Ltd | Berkshire |
| Castlegate IT Ltd | North Yorkshire |
| Castline Systems | West Sussex |
| Catalis, L.P. | |
| Catalysoft Ltd | Essex |
| Catalyst | Antrim and Newtownabbey |
| Catalyst | |
| Catalyst Internet Consultancy Ltd | Isle of Wight |
| CATalyst Systems | Denbighshire |
| Catalyst Websites Ltd | South Yorkshire |
| Catalyst, a Constellation Software Company | Leicestershire |
| Catalyst2 | Belfast |
| Catapult Network | |
| Catapult Ventures | Leicestershire |
| CatBase Publishing Systems Ltd | Hertfordshire |
| CatchApp | |
| Cater Allan Private Bank | |
| CaterBook | |
| Cathedral Web Design | Lincolnshire |
| CatSci Ltd | |
| Cattle Eye Ltd | |
| Cattleman Technologies Ltd | |
| Caura | Greater London |