| Airship Services Ltd | |
| Airsource Ltd | Cambridgeshire |
| Airsys Communications Technology Ltd | Hampshire |
| Airtechnics Ltd | |
| Airtel-Vodafone | |
| Airwave Europe Ltd | West Sussex |
| Airwave Solutions Ltd | |
| Airwer Ltd | County Durham |
| Aiviq Ltd | |
| AJ Bell | |
| AJ Computing | Lincolnshire |
| AJ New Media | Derbyshire |
| Aj-creativedesigns | |
| AJC Software | Lincolnshire |
| AJM Automation Ltd | Derbyshire |
| AJP IT Services | Bristol |
| AJR Data Recovery Services | Wiltshire |
| AKA Internet Ltd | |
| AKA Media Bolton Website Design Co. | Greater Manchester |
| Akamis Bio | |
| Akari Therapeutics plc | |
| AKCGlobal Group | |
| AKDesigner, LLC | West Yorkshire |
| Akiko | Surrey |
| AKITA Systems Ltd | Kent |
| AKL Therapeutics | Greater Manchester |
| Akona Holdings | |
| Akoova | |
| Aksa Security Ltd | |
| Aktis Computing | West Yorkshire |
| Al Rayan Bank plc | Greater London |
| 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 |
| ALB Accountancy (UK) Ltd | |
| Alba Orbital Ltd | |
| Alba SEO Services | Edinburgh |
| Albacom Ltd | Dundee |
| Alban Digital Ltd | |
| Albany Computer Services | South Yorkshire |
| Albasoft | |
| Alberon | Oxfordshire |
| Albion | West Sussex |
| Albion Capital Group, LLP | |
| AlbionVC | Greater London |
| AlbionVC | Greater London |