| Akari Therapeutics | |
| Akcela Ventures Ltd | |
| AKCGlobal Group | |
| AKD Satellite Communications Ltd | |
| AKDesigner, LLC | West Yorkshire |
| Akiko | Surrey |
| AKITA Systems Ltd | Kent |
| AKL Research & Development Ltd | |
| Akona Holdings | |
| Akoova | |
| Aksa Security Ltd | |
| Aktis Computing | West Yorkshire |
| AKY X Digital | |
| Al Bari Consulting Group | |
| Al-Junaid | |
| Al-Maktoum College of Higher Education | |
| Alacrify Ltd | Dorset |
| Alacrita Holdings Ltd | |
| Alan Howarth Computer Support | |
| Alan Turing Institute | Greater London |
| Alarm Communications Ltd | Surrey |
| Alate Creative | Greater London |
| Alba Orbital Ltd | |
| Alba SEO Services | Edinburgh |
| AlbaCo Ltd | |
| Albacom Ltd | Dundee |
| Alban Digital Ltd | |
| Albany Computer Services | South Yorkshire |
| Alberon | Oxfordshire |
| Albion | West Sussex |
| Albion | |
| Albion Capital Group, LLP | |
| AlbionVC | Greater London |
| Albumedix Ltd | |
| Albus Technologies Ltd | |
| Alchemab Therapeutics | |
| 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 | |
| Alderley Analytical Ltd | |
| Aldous Systems (Europe) Ltd | Buckinghamshire |
| Ale Valente | |