| Ascendx Cloud Ltd | |
| Ascension Ventures Ltd | Greater London |
| Ascensor | |
| Ascom (UK) Ltd | Staffordshire |
| Ascot Business Solutions Ltd | |
| Asdon Group | Lisburn and Castlereagh |
| ASE Computer Services | North Yorkshire |
| ASG Media | South Yorkshire |
| Ash Allen Design | |
| Ash Telecom | Surrey |
| ASH Wireless Electronics Ltd | |
| Ashbrook Research & Consultancy Ltd | |
| Ashby Computer Services | Northamptonshire |
| Ashdown Solutions Ltd | |
| Ashe Consulting | |
| Ashlea Components Ltd | Wiltshire |
| Ashley Bolser Agency | West Yorkshire |
| Ashman Consulting Ltd | |
| Ashmead Designs Ltd | Devon |
| Ashton Court Group | Northamptonshire |
| Asimtek IT Services | |
| ASK BOSCO | |
| ASK Technology Ltd | Hampshire |
| ASK4 Ltd | |
| ASKE Consulting | |
| ASM Development | |
| ASM Technologies Ltd | |
| Asoko Insight | |
| Asolvi | Buckinghamshire |
| AsOne | Greater Manchester |
| Aspect IT Ltd | Greater Manchester |
| Aspect Media International | |
| Aspect Training | Greater London |
| Aspen Solutions Ltd | North Lanarkshire |
| Aspen Web Designs | West Sussex |
| Aspilogic | |
| Aspira Software Solutions | |
| Aspire Creative | |
| Aspire Digital Marketing | |
| Aspire IT Services Ltd | |
| Assembler (DCI) Ltd | Cheshire |
| Assembly Care Tech Ltd | |
| Assembly Contracts Ltd | Greater Manchester |
| Assembly Solutions Ltd | Greater Manchester |
| Assemblysoft Ltd | |
| Assent | Essex |
| Assertive Media | |
| Assertive Media Solutions Ltd | |
| Assessor Consulting | |
| AssessTech Ltd | |