| Albumedix Ltd | |
| Albus Technologies Ltd | |
| Alchemab Therapeutics Ltd | |
| Alchemist Studios | |
| Alchemy Digital | Greater London |
| Alchemy Interactive Ltd | Greater London |
| Alchemy Machines Ltd | |
| Alchemy Online Ltd | Buckinghamshire |
| Alchemy Systems | Surrey |
| Alcium Software Ltd | |
| Alcohol Soft | Belfast |
| Alcyomics Ltd | |
| Alden Legal | |
| Alder Hey Innovation Lab | |
| Aldermore Bank plc | |
| Aldous Systems (Europe) Ltd | Buckinghamshire |
| Ale Valente | |
| Alembic Design Consultants | Hertfordshire |
| Aleron Partners Ltd | |
| Alert Logic | |
| Alertacall Ltd | |
| AlertSystems Ltd | Wiltshire |
| Alesi Surgical Ltd | |
| Alex Curtis | Bristol |
| Alexander & Co., LLP | |
| Alexander James Technology | Kent |
| Alexander Mann Solutions | |
| AlexSys Communications Ltd | |
| Algbra | |
| AlgolOnline | Ceredigion |
| Algorand Europe Accelerator | |
| Algotron Ltd | Surrey |
| Alicia Sykes | |
| Alight Solutions | |
| Aligned Assets Ltd | Surrey |
| Alistair Whiteley | Somerset |
| Alistair Whiteley Web Design Ltd | |
| All Interactive Ltd | Hampshire |
| All My Ink | Norfolk |
| All My Systems Ltd | |
| All Net Solutions Ltd | |
| All Round Web Design | Derbyshire |
| All The Top Bananas | Lincolnshire |
| All Top Notch | Cheshire |
| All Web Services Ltd | Gloucestershire |
| All.Space Networks Ltd | |
| Allday Time Systems | Hampshire |
| Allegro Capital Ltd | |
| Allen Computer Services | |
| Allergy Therapeutics plc | |