| Appoly | Warwickshire |
| Approach Direct Marketing | |
| Appropriate Solutions | Cumbria |
| ApprovalMax | |
| Approved Index | |
| Apps in My Pocket | |
| Apps IT Ltd | |
| Apps On The Move Ltd | |
| Apps Plus | West Midlands |
| Appsecco | |
| AppShed Ltd | |
| Appsmakerstore | |
| Appsumer | |
| Apptituda | |
| Apptivation Mobile Ltd | |
| Appuals | Dorset |
| Appurity | |
| AppWeb | |
| AppyParking | |
| AppyWay | |
| Apricity Fertility UK Ltd | |
| Apricot | Gloucestershire |
| Apricus Med-Tech UK Ltd | |
| Apritel Communication Services | Hampshire |
| Aprompt | Wiltshire |
| Apron Payments Ltd | |
| APT Ltd | Greater London |
| APT Solutions Ltd | Shropshire |
| Apteco Ltd | Warwickshire |
| Aptem Ltd | |
| Aptitude Software Ltd | |
| Aptive Consulting Ltd | Surrey |
| Apto Solutions | Bristol |
| Aqdot Ltd | |
| Aqilla | |
| aql | West Yorkshire |
| Aquaforest | Buckinghamshire |
| Aquamarine Media | |
| Aquamatix Ltd | |
| AquaQ Analytics | |
| Aquatec Group Ltd | |
| Aquila Software | Kent |
| AR Digital Solutions Ltd | Devon |
| Arabesque | |
| Arachsys Internet Services Ltd | Shropshire |
| Aragon Consulting Services Ltd | Lancashire |
| Aralia Systems | |
| Araucaria Computing | Edinburgh |
| Araxis Ltd | Isle of Man |
| Arbico | Greater London |