| Domainex | |
| DomainNameShop.co.uk | Glasgow |
| Domicilium (IOM) Ltd | Isle of Man |
| Dominion Digital | |
| Doncaster Apps | |
| DoodleIT Ltd | Denbighshire |
| Door 105 | Greater London |
| Door4 | Lancashire |
| Doping Technology | |
| Dorset Linux User Group | Dorset |
| Dorset Software | |
| Dorset Web | Dorset |
| DOT | Lancashire |
| Dot Group | Greater London |
| Dot Residential Ltd | |
| Dot Software Ltd | Somerset |
| Dot Solutions and Technologies | Kent |
| DOT-COMmunICaTions | West Yorkshire |
| DotCentric Ltd | |
| Dotcraft | |
| DotGO | Surrey |
| dotnet | |
| DotNet We Hosting UK | West Midlands |
| DotNetted | Northamptonshire |
| DotOxygen | |
| DotPerformance | Isle of Man |
| dotRetailer.com | Ards and North Down |
| DotScot | Glasgow |
| Dotsquares Ltd | West Sussex |
| Doublard Design | East Sussex |
| Double Digit Media | |
| Double Eleven Ltd | North Yorkshire |
| Doublesided | |
| Doublespark Internet Marketing | Cambridgeshire |
| Douglas | |
| Douglass Digital | |
| Doulos Ltd | Hampshire |
| Dove Computer Solutions Ltd | |
| Dove Internet | Derbyshire |
| Dovestones Software | Greater Manchester |
| Dovetail Games | |
| DOVU Ltd | |
| Downing Enterprise | |
| Downing IP Ltd | |
| Downing Ventures | |
| Downline Media | Newry, Mourne and Down |
| DOWO Digital Ltd | Greater Manchester |
| Doza Consulting | |
| DP Connect | Greater London |
| DPG Ltd | |