| 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 |
| CAD Services | Essex |
| CAD User Magazine | Greater London |
| Cad-Capture | Lancashire |
| CADagency | |
| Cadan Design Digital | |
| CADCentre UK | Swansea |
| Caddie Software | Bedfordshire |
| Cademy | |
| Cadenergy Ltd | Fife |
| CADify | |
| CADline | Surrey |
| CADlogic Ltd | Staffordshire |
| Cado Security | |
| CADS | Dorset |
| CADS Ltd | Derbyshire |
| Cadspec | Worcestershire |
| CADsultants Ltd | Greater London |
| Caeli Nova | |
| Caesar | |
| Caged Fish | |
| Cairn Creative | Aberdeenshire |
| Cairngorm Capital | Greater London |
| Caistar | Denbighshire |
| CaixaBank, S.A., UK Branch | |
| CaJSoft Ltd | |
| Cake Agency | |
| Cal Partners Ltd | |
| CAL Services UK Ltd | Somerset |
| Calculus Software Solutions Ltd | |
| Caldan Therapeutics Ltd | |
| Calderdale College | |
| Calderdale Computer Services | West Yorkshire |
| Caledonian Cables Ltd | East Sussex |
| Caletech International Ltd | Angus |
| Caliach Ltd | Devon |
| Calica Computer Solutions | |
| Calico UK | Highland |
| Caligo Ltd | Channel Islands |