| Clarity Ltd | |
| Clarity Software | Staffordshire |
| Clarivate | |
| Clark Communications Ltd | |
| Clark Electronic Consultants Ltd | Stirling |
| Clark Studios Ltd | |
| Clarke Computer Systems | |
| Clarke Telecom | |
| Clarkson Computer Sales Repairs | |
| Claro Software Ltd | Lancashire |
| Claromentis | East Sussex |
| Clarydon Electronic Services Ltd | West Midlands |
| Class Creative Ltd | |
| Class Systems | Dorset |
| Class Technology Solutions | |
| ClassForKids | |
| ClassForKids | |
| Clausematch | Greater London |
| Claytex Services Ltd | Warwickshire |
| Clayton | |
| CLD | Berkshire |
| Clean Digital Ltd | |
| Clean Energy Consultancy Ltd | |
| Cleantech Innovate | |
| Clear Books plc | Greater London |
| Clear Cloud Computing Services Ltd | Lincolnshire |
| Clear Design UK Ltd | Bristol |
| Clear Line Tech | East Sussex |
| Clear Software | |
| Clear Surgical | |
| Clear Thinking (Software) Ltd | East Sussex |
| Clear Vision Systems | East Riding of Yorkshire |
| Clear Visual Communications Ltd | |
| ClearBank Ltd | Greater London |
| ClearBrand Ltd | |
| Clearcare Solutions Ltd | |
| ClearCrypt | |
| ClearDebit | |
| Cleardrop Ltd | Essex |
| ClearFibre Ltd | |
| clearFusion Digital | Cornwall |
| Clearleft Ltd | |
| ClearLine Communications Ltd | |
| Clearsight Consulting | |
| Clearsite Ltd | Channel Islands |
| ClearSky Logic Ltd | |
| Cleartarn Ltd | |
| Cleartext Systems Cyber | |
| Cleartwo | |
| Clearwater IT Services | |