| Aberdeen Internet | Aberdeen |
| Abertay University | Dundee |
| Abertay University - Department of Games Technology and Mathematics | Dundee |
| Aberystwyth University | Ceredigion |
| Aberystwyth University - Department of Computer Science | Ceredigion |
| Abey Foundation | |
| Abilas IT Ltd | Greater Manchester |
| Ability First Ltd | |
| Ability Software Consultants | Gloucestershire |
| AbilityNet | Berkshire |
| Abingdon Health | |
| Abingworth, LLP | |
| Abipo | Craigavon |
| Abiquo Europe Ltd | Greater London |
| Abisti Web Consultants | East Sussex |
| ABL Circuits Ltd | Hertfordshire |
| Ably | Greater London |
| ABNK Premium Systems | |
| AbOliGo Ltd | |
| About Now Ltd | |
| Above Creative | West Sussex |
| ABPC Ltd | North Yorkshire |
| Abra Millar Ltd | |
| abrdn plc | |
| ABS Ltd | Buckinghamshire |
| Abselion | |
| Absmax Web Design | Edinburgh |
| Absoft Ltd | Aberdeen |
| Absolute Antibody | |
| Absolute Creative Marketing Ltd | Gloucestershire |
| Absolute Design Associates Ltd | Nottinghamshire |
| Absolute Digital Media Ltd | |
| Absolute ICT Services | |
| Absolute Integrated Agency Ltd | |
| Absolute Internet Marketing | Leicestershire |
| Absolute Micro Communications | Buckinghamshire |
| Absolute Network Solutions Ltd | Denbighshire |
| Absolute Networks Ltd | Nottinghamshire |
| Absolute Technology (UK) Ltd | Hampshire |
| Absolute Web Design Ltd | South Yorkshire |
| Absolutely PC | |
| Absowebly Ltd | Surrey |
| ABSSoftware | |
| Abstract Tech | |
| Abstraction Labs Ltd | |
| Abstraction Web Design Experts | |
| Abstrakt Creative Ltd | Nottinghamshire |
| Absurd Ltd | |
| Abtec Computer Solutions | Greater Manchester |
| Abtec Network Systems Ltd | Leicestershire |