| C-MI Corporation EMEA | Surrey |
| C-Plan Telecommunications | |
| C. Hoare & Co. | |
| C.A. Designs (Leicester) Ltd | Leicestershire |
| C.A.I. Vision Systems Ltd | Greater London |
| C.Itoi Ltd | Lincolnshire |
| C2 IT Asset Disposal Ltd | |
| C2 Software | Dundee |
| C3 Ltd | Cambridgeshire |
| C3 Media Ltd | |
| C4DI Ltd | East Riding of Yorkshire |
| C4XD Holdings Ltd | |
| C4XD Holdings plc | |
| C5 Alliance | Channel Islands |
| C5 Capital | |
| Cab Engine | |
| Cab Guru Ltd | |
| Cab Studios | |
| Cab:app | |
| Cable & Wireless Communications Ltd | |
| Cable Communications | Norfolk |
| Cable Consulting International Ltd | |
| Cable Harnesses UK Ltd | Carmarthenshire |
| Cable Intelligence | Gloucestershire |
| Cable Monkey | Essex |
| Cable Services Ltd | Wrexham County Borough |
| Cable Systems Ltd | Cheshire |
| Cable Tec Cables & Controls Ltd | Nottinghamshire |
| Cable Ties | South Yorkshire |
| Cable-Talk UK Ltd | West Yorkshire |
| Cable.co.uk | |
| Cablecraft Ltd | Bedfordshire |
| Cabledan | |
| Cablefree | Oxfordshire |
| CableJog Ltd | Cheshire |
| Cablelynx Ltd | Northamptonshire |
| Cablenet Ltd | Surrey |
| Cables and More | Hertfordshire |
| Cables Direct Ltd | Derbyshire |
| CableSpeed | Lancashire |
| Cabletec | Somerset |
| Cablevine Solutions Ltd | Somerset |
| Caboodle Digital Ltd | Greater London |
| Caboodle Office Supplies | Hampshire |
| Cache Digital | |
| Cachet | |
| Cactusoft Ltd | Hampshire |
| CAD Bureau Southern Ltd | Essex |
| CAd dot Services | Swansea |
| CAD Schroer UK Ltd | Cambridgeshire |