| Activ Web Design | West Yorkshire |
| ActivAeon Ltd | |
| Activate Digital Ltd | |
| Activate Studio | |
| Active Alliance Ltd | Cambridgeshire |
| Active Digital Communication Ltd | Kent |
| Active Electronics plc | Buckinghamshire |
| Active Housing | |
| Active Internet Marketing (UK) | |
| Active Merchant Services Ltd | |
| Active Mind Solutions | |
| Active Navigation | Hampshire |
| Active Office | East Ayrshire |
| Active Partners Investments, LLP | |
| Active Pharma Supplies Ltd | |
| Active Robots Ltd | Somerset |
| Active Solutions Ltd | Lancashire |
| Active Webdezign Ltd | |
| Active-PCB Solutions Ltd | Berkshire |
| ActiveOps Ltd | Berkshire |
| Activereach Ltd | |
| Activesol | Hampshire |
| Actopia | Buckinghamshire |
| Acttron Ltd | Hertfordshire |
| Acu IT Solutions | Glasgow |
| Acua Ocean | |
| AcuIT Ltd | Kent |
| Acuiti Labs | |
| Acuity Advisors Ltd | |
| 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 | |
| Acutec Ltd | |
| acuteFX Design Ltd | Leicestershire |
| Acuutech | |
| Acuvate | |
| ACW | Greater London |
| AD Computers | |
| AD Global Consulting Services Ltd | |
| Ad Idem Consulting Ltd | |
| Ad Rank One Ltd | |
| Ad-tivity | |
| Adaccus Internet Marketing Consultants | Surrey |
| Adadot | |