| Alliance Group | North Yorkshire |
| Alliance Pharma plc | |
| Alliance Solutions | Hertfordshire |
| Alliance Systems Ltd | Bristol |
| Alliance Trust plc | |
| Allied Computers International Ltd | Greater London |
| Allied Irish Bank (GB) | |
| Allied Telecoms Ltd | Essex |
| Allied Worldwide Ltd | Buckinghamshire |
| Allies Computing Ltd | Norfolk |
| Allman Horrocks Consulting Ltd | Warwickshire |
| Allocate Software Ltd | Greater London |
| Allocate UK | Greater London |
| Allotrope Energy Ltd | |
| Alloxentric | |
| Allsee Technologies Ltd | |
| Allstar Media Services | |
| AllStarsWomen NFT Club & DAO | |
| Alltek Solutions Ltd | Shropshire |
| Allteks Ltd | Kent |
| allthe.domains | |
| Aln Technology Ltd | |
| Alniro Ltd | Hampshire |
| Aloniq | |
| Alpha Bank London Ltd | |
| Alpha Digital Solutions Ltd | Derbyshire |
| Alpha Electronics | Kent |
| Alpha Sate | East Sussex |
| Alpha Scan Computers Ltd | Hampshire |
| Alphabtye IT | Cardiff |
| Alphacom Telecoms | Greater Manchester |
| Alphanet Ltd | |
| Alphanet Web Design | |
| Alphapc Ltd | Cheshire |
| AlphaQuad Ltd | Warwickshire |
| alphaTALK Ltd | West Midlands |
| Alphatec Software Ltd | North Lanarkshire |
| Alpine Interactive UK Ltd | |
| Alpine Technology | East Sussex |
| ALR Services Ltd | Oxfordshire |
| Alrad Instruments Ltd | Berkshire |
| ALSA Ventures | |
| Alscient | |
| ALT 21 Ltd | |
| ALT Agency | West Midlands |
| AltaClub | Gibraltar |
| Altacor Ltd | |
| Altcom Ltd | Cornwall |
| Altered | |
| Alternative Communication Systems | Oxfordshire |