| Abisti Web Consultants | East Sussex |
| ABL Circuits Ltd | Hertfordshire |
| Ably | Greater London |
| ABNK Premium Systems | |
| Abodoo | |
| 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 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 | |
| Abstrakt Creative Ltd | |
| Abtec Computer Solutions | Greater Manchester |
| Abtec Network Systems Ltd | Leicestershire |
| Abtrace | |
| Abussi Ltd | West Midlands |
| ABVentures | |
| Abzena plc | |
| AC Computer Warehouse Ltd | Greater Manchester |
| AC Database Services Ltd | |
| AC Plus | Essex |
| Ac-Sys Ltd | West Yorkshire |
| ACA Systems | |
| Acacia Pharma Group plc | |
| Acacia Training Ltd | |
| Academy Networks | Berkshire |
| Acal BFi Ltd | Berkshire |
| Accappella Creative Ltd | |
| Acceler8 Clinical Research Ltd | |
| Accelerated Digital Ventures | |
| AccelerateMe | |
| AccelerateME | |