| Datatrack | Dorset |
| Datatrack Labs | |
| DataVita Ltd | |
| Dataware Consultancy Centre Ltd | Essex |
| Datech Solutions Ltd | Kent |
| Datek Solutions | Berkshire |
| Datrock | |
| Datum Electronics Ltd | Isle of Wight |
| DAU Components Ltd | West Sussex |
| Daval Computers Shop | Cambridgeshire |
| Dave Harrison | |
| Dave Piers Computer Services | |
| Dave Stewart | |
| Davel Technology | Stirling |
| DaveWoods | Cumbria |
| David Airey | |
| David Henderson Design | Belfast |
| David James Graphic Design | |
| David Kelly Design Office | |
| David Nye | Surrey |
| David Silver | |
| Davies Wise Design Company | Gloucestershire |
| Davis Solutions Ltd | |
| Davtech Computers | |
| Davydov Consulting Ltd | |
| Daw Systems Ltd | Aberdeen |
| Dawley Web Design | Shropshire |
| Dawn Capital | |
| Dawson Design | Greater Manchester |
| DAX Automation Ltd | |
| Daxesoft Ltd | Cheshire |
| Daydream | |
| Daye Ltd | Greater London |
| Dayford Designs | Gloucestershire |
| Daykin & Storey | Tyne and Wear |
| Daytrip Europe Ltd | |
| db audioware Ltd | Glasgow |
| DB Systems Ltd | Gloucestershire |
| DBA Consultancy | Berkshire |
| DBaaS Ltd | |
| DBETA | |
| DBL Software Ltd | Wiltshire |
| dBMasters Ltd | Kent |
| DBS Datamarketing Ltd | |
| DBS Digital | |
| DC Biosciences | |
| Dccscotland | |
| DCP | |
| DCRS | Cambridgeshire |
| DCSL Software Ltd | Hampshire |