| DS Creative | |
| DS Data Systems (UK) Ltd | Buckinghamshire |
| DS.Emotion | West Yorkshire |
| Dsgn One | Somerset |
| DSKY Digital Agency | |
| DSM Design Ltd | Dorset |
| DSM GB Ltd | Cambridgeshire |
| DSM Systems Ltd | |
| DSPG Telecom | Greater London |
| DTC-Telecom | Northamptonshire |
| DTec Computers | Cumbria |
| Dtech Systems | |
| DTF Digital | West Yorkshire |
| DTG | |
| DTS Digital | North Yorkshire |
| DTTUK | Berkshire |
| Dtwo Creative Ltd | |
| du Pré plc | Berkshire |
| Dual Media Ltd | Lancashire |
| Duality Studio | |
| Dubit | West Yorkshire |
| DubSEO Ltd | |
| Duck Feet | |
| Duck on water | Gloucestershire |
| Duck.Design | |
| Duco | Greater London |
| Due Ltd | |
| Duel | |
| Duel Marketing | |
| Duffel Technology Ltd | |
| Duke Street Bio Ltd | Greater London |
| Dukosi Ltd | |
| Dun & Bradstreet | Buckinghamshire |
| Duncan Wedddell & Co. | Edinburgh |
| Dunedin IT | |
| Dunne Roberts Ltd | Hampshire |
| dunnhumby | |
| Dunstan Thomas Group Ltd | Hampshire |
| Duo Creative Services Ltd | Greater Manchester |
| Duplex Thermal Printers | Lancashire |
| Duplication Centre | Essex |
| Duplidisk Ltd | Devon |
| Durham Linux User Group | County Durham |
| Durham University | County Durham |
| Durham University - Department of Computer Science | County Durham |
| Durham University - Department of Mathematical Sciences | County Durham |
| Dusza Ltd | Dorset |
| DVD Plus | |
| DVH Design | |
| DVI Technologies | |