| Accelerator Academy | |
| Accelerator London | Greater London |
| Accelerator Ltd | |
| AccelerComm Ltd | |
| Accelex Technology Ltd | |
| Accellabs Development | Greater London |
| Accentra Technologies Ltd | Greater London |
| Accentus Medical Ltd | |
| AcceptPhones.com | |
| Access and Security Systems Ltd | Berkshire |
| Access Computing Solutions Ltd | Buckinghamshire |
| Access Control UK | Essex |
| Access Ltd | Berkshire |
| Access Networks Solutions Ltd | Greater London |
| Access Partnership Ltd | |
| Access Volcanic | |
| accesso Technology Group plc | Berkshire |
| accesso Technology Group plc | |
| AccessPay | |
| Accessplanit | |
| Accord Healthcare | |
| accountsIQ | Kent |
| AccountsPortal | |
| Accrofab | |
| Accsys Accountants Ltd | |
| accSYS Digital Ltd | |
| Accupart Ltd | Greater Manchester |
| AccuraData | |
| Accurx | |
| AccuStem Sciences, Inc. | Greater London |
| AccuTime Ltd | Cheshire |
| Accutronics Ltd | Staffordshire |
| Accuvio | |
| Accuweb (Brighton) Ltd | |
| Ace Multimedia | Worcestershire |
| ACE Security | |
| ACEL Systems Ltd | Nottinghamshire |
| Aceleron Ltd | |
| Acellera | |
| AceShells Internet Services | East Sussex |
| Acess Creative College | |
| AceTech Enterprises | Berkshire |
| ACF Investors | South Yorkshire |
| ACG Consulting | Greater London |
| Achieve Intelligence | |
| Achilles Therapeutics plc | |
| Achroma.co.uk | Lancashire |
| Acin | Greater London |
| ACL Comms Ltd | Cheshire |
| ACl Exhibitions Ltd | |