| Acuity Knowledge Partners | |
| Acuity Software Technologies Ltd | |
| Acuity Training | Greater London |
| Aculab | Buckinghamshire |
| Acuma Solutions | Greater Manchester |
| Acumen Business Systems Ltd | West Midlands |
| Acurable | |
| Acuras Ltd | Buckinghamshire |
| Acuris Risk Intelligence Ltd | |
| acuteFX Design Ltd | Leicestershire |
| Acuutech | |
| ACW | Greater London |
| AD Computers | |
| Ad Idem Consulting Ltd | |
| Ad Rank One Ltd | |
| Adaccus Internet Marketing Consultants | Surrey |
| Adadot | |
| Adalta | |
| Adam Appointments | |
| Adam Bradford Ltd | |
| ADAM Continuity | Hampshire |
| Adam Matthew Digital Ltd | |
| ADAMAPP | |
| Adams Group | Kent |
| Adams IT Services UK | |
| Adappt | Greater London |
| Adapt IT Recruitment Ltd | Buckinghamshire |
| Adapt Studios | |
| Adapt Worldwide | |
| Adaptatech | Greater London |
| Adaptavate Ltd | |
| Adaptimmune Therapeutics plc | |
| Adaptive Automation | |
| Adaptive Conversions | Greater London |
| Adaptive Modules Ltd | East Sussex |
| Adaptive SEO | |
| Adaptive SEO | |
| Adaptive Web Ltd | Derbyshire |
| Adaptive Wireless Solutions Ltd | Oxfordshire |
| Adaptix Ltd | |
| Adaptsys Ltd | |
| Adarga | |
| Adastral Park | Suffolk |
| Adavatek | Wrexham County Borough |
| AdCombo | |
| Add Creative | Dorset |
| Add People | Greater Manchester |
| Added Bytes Ltd | |
| Adder Technology Ltd | Cambridgeshire |
| Addictivity | Greater London |