| Amethyst Risk Management Ltd | Hampshire |
| AMFG | |
| AMG IT Solutions | Staffordshire |
| AMG Systems Ltd | Bedfordshire |
| Amigaworld.net | Belfast |
| Amimetic | |
| Amine Dahimene - SEO Expert | |
| Amino Communications | |
| Amiqus Resolution Ltd | |
| Amito Ltd | Berkshire |
| AMJ UK | Kent |
| AML Analytics Ltd | |
| AML Technology | Dumfries and Galloway |
| AMLo Biosciences Ltd | |
| Ammara | Surrey |
| AMO Pharma Ltd | |
| Amoo | |
| AMP Computer Maintenance | |
| AMP Studio | |
| Amparo Prosthetics Ltd | |
| Amped PCR | |
| Ampersand | Greater Manchester |
| Ampersand & Ampersand | |
| AMPG IT Services | South Yorkshire |
| Amphis Software | Somerset |
| Amphista Therapeutics Ltd | |
| Amphora | |
| Amplicon Liveline Ltd | East Sussex |
| Amplience | |
| AmplifyMe | Aberdeen |
| Ampliphae | |
| AMS Biotechnology | |
| Amshire Solutions Ltd | Greater Manchester |
| Amsys Ltd | Greater London |
| AMT Auto | |
| AMT Data Technologies Ltd | Hampshire |
| Amuzo Ltd | Dorset |
| AMX Solutions Ltd | |
| AN4 Group Ltd | Hampshire |
| AnaCap | |
| Anachron Technologies Ltd | |
| Anagram Systems Ltd | |
| Analog Studio | |
| Analogue Integration Ltd | Wiltshire |
| Analox Instruments Ltd | |
| Analyse-it | West Yorkshire |
| Analysys Mason | |
| Analytical Technology and Control Ltd | Wiltshire |
| Anamosys | |
| Anaphite Ltd | |