| Cirdan | |
| Cirencester Computer Repairs Ltd | Gloucestershire |
| Cirrus Logistics Ltd | Hampshire |
| Cirrus Software | Buckinghamshire |
| CirrusHQ | West Lothian |
| Cisillion | Surrey |
| Citation Cyber Ltd | |
| Cite | |
| Citel | Leicestershire |
| CitizenMe | |
| CitizenMe Ltd | |
| CitNOW | |
| Citrixit Consultancy | |
| City College Norwich | |
| City Computing Ltd | Greater London |
| City Falcon Ltd | |
| City Ink Express Ltd | Derbyshire |
| City Numbers Ltd | |
| City of Glasgow College | |
| City PC Repairs | Edinburgh |
| City St George's, University of London - School of Science & Technology | Greater London |
| City, University of London | Greater London |
| City, University of London - Centre for Software Reliability | Greater London |
| City, University of London - London Space Innovation Centre | Greater London |
| Citydeal Estates | |
| CityFleet Networks Ltd | |
| CityJS | |
| Cityscape Digital | |
| CIVIC | Edinburgh |
| Civica | Greater London |
| Civo | Greater London |
| Cizzle Biotech | |
| CJ Systems | |
| CJB Interactive | West Midlands |
| CJE Micro's | West Sussex |
| CJS Engineering Ltd | Gloucestershire |
| CJT Group Ltd | Essex |
| CK Systems | |
| CKS Global Solutions Ltd | Hertfordshire |
| ClamXav | Edinburgh |
| Claranet Group Ltd | Greater London |
| Claranet SOHO | Cheshire |
| Clare Associates Ltd | Cornwall |
| Clarilis Ltd | |
| Clarion Communication Systems Ltd | |
| Clarisign | |
| Claritech Ltd | |
| Clarity Growth Ltd | |
| Clarity London Ltd | Greater London |
| Clarity London Ltd | |