| Compass Pathways | Greater London |
| compassion-in-business | Hertfordshire |
| Compatibility Ltd | East Sussex |
| Compendium Developments Ltd | Hertfordshire |
| Competence Development Ltd | |
| Competera Ltd | |
| Compfix International | |
| Compiforce Ltd | Northamptonshire |
| Compilator | |
| CompileQ Ltd | |
| Complement Genomics | |
| Complete Communications (Essex) Ltd | Greater London |
| Complete Computer Solutions | |
| Complete Computer Systems Ltd | |
| Complete IT | Buckinghamshire |
| Complete Marketing Solutions | |
| Complete Office Solutions | West Yorkshire |
| Complete Telecoms Ltd | Worcestershire |
| Complete Training Solutions Ltd | |
| Compliance Labelling Solutions Ltd | Essex |
| Compliance Studio Ltd | |
| Complink | Derbyshire |
| Complx.co | |
| ComplyAdvantage | |
| Component Sense | West Lothian |
| Compositional IT | |
| Compound Semiconductor | West Midlands |
| Compsoft (UK) Ltd | Hampshire |
| Compu Lease | Cheshire |
| Compu-K (Cornwall) Ltd | Cornwall |
| Compu-tech | Devon |
| CompuBoss Ltd | Cheshire |
| Compuco Ltd | |
| CompuDOS | |
| Compunet Systems Ltd | |
| Compusense-UK Ltd | Essex |
| Computacenter plc | Hertfordshire |
| Computair Ltd | Bedfordshire |
| Computalabel International | Leicestershire |
| Computaplace | |
| Compute4U Ltd | Kent |
| Computeam Ltd | Greater Manchester |
| CompuTech Services Ltd | Isle of Man |
| Computek Consultancy | Rhondda Cynon Taf |
| Computency Ltd | Berkshire |
| Computer & Control Systems Ltd | West Lothian |
| Computer Advice Centre | |
| Computer Aided Development Corporation Ltd | Hertfordshire |
| Computer Angels | Greater London |
| Computer Application Services Ltd | Edinburgh |