| Auddy Ltd | |
| AuDeo | Hampshire |
| Audience2Media | Greater London |
| Audiense | |
| Audio Sanctuary | Greater London |
| Audio Visual Intelligence | |
| Audioboom Ltd | |
| AudioMate | Greater Manchester |
| Audiomob | |
| Audioscenic | |
| AudioStack | |
| AudioStrip | |
| Audiotel International | Northamptonshire |
| AudioTelligence | |
| Audiowings | |
| AuditWare Ltd | |
| Audium Ltd | Oxfordshire |
| Audon Electronics Ltd | Cheshire |
| Audoo Ltd | |
| Augmented Hype | |
| Augmented Text Company Ltd | |
| Augmentum Fintech Management Ltd | Greater London |
| Augmetic | |
| Augmize | |
| Augnet Ltd | |
| Aula Education Ltd | Greater London |
| Auquan | |
| Aura Computers | |
| Aura Creative Media Ltd | North Yorkshire |
| Aura Vision Labs | |
| Auris Tech Ltd | |
| Aurity | |
| Aurora | |
| Aurora Tech Support | |
| Aurora Technologies Ltd | Leicestershire |
| Aurum Biosciences Ltd | |
| Aurum Solutions | |
| Authentic Style Ltd | Dorset |
| Authentiq | |
| Author Studios Ltd | |
| Autifony Therapeutics | Hertfordshire |
| Auto Extract Systems Ltd | |
| Auto Marine Cables Ltd | Greater Manchester |
| Auto Mate Systems | |
| Auto Soft | Surrey |
| Auto Time Solutions Ltd | West Midlands |
| Auto Time Systems Northern Ltd | Greater Manchester |
| AutoAlert Ltd | |
| Autoblogging | |
| Autocab GPC Software Ltd | Greater Manchester |