| Defensor Security | West Sussex |
| Definely | |
| DefiniGEN Ltd | |
| Definition Consulting Ltd | |
| Deft Creative | East Sussex |
| Defy Logic Ltd | Derbyshire |
| degal | Hampshire |
| Degree 53 | Greater Manchester |
| DeHealth | |
| Dekko Ltd | Buckinghamshire |
| Dektron Ltd | Wiltshire |
| Delete Ltd | West Yorkshire |
| Delian Alliance Industries | |
| Delicious Media Ltd | South Yorkshire |
| Delicious Webdesign | Essex |
| Deligo Vision Technologies Ltd | |
| Deliver Biosciences | |
| Deliveroo | |
| DeliveryApp | |
| Delivix | |
| Delstree | Warwickshire |
| Delta Capital | |
| Delta Communications | |
| Delta Computer Services | East Sussex |
| Delta Computing Ltd | |
| Delta Digital Ltd | |
| Delta g Ltd | |
| DeltaXML Ltd | Worcestershire |
| Democratise | Greater London |
| Demon Solutions Ltd | Surrey |
| DemonSoft Ltd | |
| Denaploy | East Sussex |
| Denca Controls Ltd | Cheshire |
| Dennis Fisher Associates | Cheshire |
| Denovo Business Intelligence Ltd | Glasgow |
| Dense Air | |
| Dent Global | |
| Dentally | |
| dentsu X | |
| Dentsys Ltd | |
| Deontics Ltd | |
| Deployed | |
| Deployflow | |
| Dereham Computer Services | |
| Deriv.com Ltd | Channel Islands |
| Desana Network Ltd | |
| Desia Ltd | |
| Design & Printing Solutions Ltd | |
| Design 365 Solutions Ltd | County Durham |
| Design Agency | Bedfordshire |