| Attend a Lock Blackpool Limited | Blackpool | 2023 |
| Attention Productions Limited | Reading | 2013 |
| Attheraces (UK) Limited | London | 2001 |
| Attic Conversions (Sales) Limited | Surrey | 1997 |
| Attic.Studio International Ltd | London | 2022 |
| Atticus & Edward Ltd | Belfast | 2016 |
| Attire Holdings Ltd | Birmingham | 2021 |
| Attis Consulting Ltd | London | 2022 |
| Attis Group Limited | Leeds | 2020 |
| Attis Investments Ltd | London | 2015 |
| Attis Sport Limited | Leeds | 2021 |
| Attlee Bains Churchill Limited | Watford | 2010 |
| Attmere Plant Repairs Ltd | Colchester | 2022 |
| Attraction Safety Limited | Moor Row | 2024 |
| Attraversa Limited | London | 2013 |
| Attree and Kent Limited | Burgess Hill | 1904 |
| Attune Advisory (Cambridge) Limited | Cambridge | 2026 |
| Attunement Group Ltd | Stamford | 2026 |
| Attwood Farms Limited | Chatham | 1996 |
| ATU Yachting Ltd | London | 2025 |
| ATULKAN0 Ltd | Watford | 2024 |
| Atum Healthcare Limited | Horley | 2023 |
| Atun Yachting Ltd | London | 2025 |
| Atvantic Partners Nordic Limited | London | 2022 |
| Atwell Labellers Limited | St. Austell | 1996 |
| Atwell Self-Adhesive Labellers Limited | St. Austell | 1996 |
| ATY Engineering Ltd | London | 2016 |
| Atzler Limited | London | 2018 |
| AU Guys Ltd | Camborne | 2023 |
| AU Plus Ltd | Doncaster | 2016 |
| Au-Pair International Ltd. | Sittingbourne | 2002 |
| AU1 Investments Ltd | Coventry | 2024 |
| Auburn Apple Developments Limited | Newton Abbot | 2011 |
| Auburys Limited | London | 2014 |
| AUC Cleaning Services Ltd | Luton | 2023 |
| Auchans Limited | Johnstone | 2013 |
| Auchattie Community Trust | Banchory | 2015 |
| Auckland 1966 Limited | Birmingham | 2013 |
| Auckland Hill Associates Limited | London | 2012 |
| Auction 4 Cars Limited | Derby | 2015 |
| Auction Central Limited | Birmingham | 2011 |
| Auction Finance Limited | Bury | 2014 |
| Auction Rooms (Brighton) Management Limited | Hove | 2013 |
| Auction.London Ltd | London | 2015 |
| Audable Ltd | Truro | 2019 |
| Audax Overseas Holding Ltd | London | 2022 |
| Audax Sound System Limited | Rotherham | 1964 |
| Audel Limited | Plymouth | 2012 |
| Audenham Limited | Brierley Hill | 2010 |
| Audens Way 1970 Limited | Swadlincote | 2014 |
| Audentia Capital Ltd | London | 2020 |
| Audere Limited | London | 2012 |
| Audio Books on Tape Limited | Stonehouse | 2015 |
| Audio Calibre Ltd | London | 2024 |
| Audio Delight Limited | Birmingham | 2009 |
| Audio Tech Limited | Buxton | 2025 |
| Audioforce Limited | Cambridge | 2007 |
| Audiolance International Ltd | London | 2024 |
| Audiophonics Limited | London | 2009 |
| Audioprint Management Limited | Bedford | 2009 |
| Audire Care Limited | Liverpool | 2022 |
| Audit & Consult Ltd | Stockport | 2013 |
| Audit Assured Limited | London | 2025 |
| Audit Coms Ltd | Chorley | 2015 |
| Audit Direct Ltd | Preston | 2013 |
| Audita Group Ltd | Romford | 2015 |
| Auditbook Ltd | London | 2025 |
| Auditel Consulting Limited | Kingston Upon Thames | 2002 |
| Auditel Limited | Kingston Upon Thames | 2007 |
| Auditfree (Nominees) Limited | Boreham Wood | 1998 |
| Auditors Limited | Kent | 1995 |
| Audley Management Properties Ltd | London | 2004 |
| Audley Millennium Green Limited | Stoke-On-Trent | 2013 |
| Audley Properties Services Limited | Bracknell | 1995 |
| Audrey (London) Limited | Chertsey | 1961 |
| Audrey Grace Ltd | Hitchin | 2024 |
| Audrey Lindsay Ltd | London | 2025 |
| Audreybeth Ltd | Rochester | 2022 |
| Audrius Gudas Ltd | Colchester | 2026 |
| Auenland Ltd | London | 2022 |
| Aufiss International Industries Limited | Cambridge | 2015 |
| AUG Management Limited | Birmingham | 2007 |
| Augean Incineration Limited | Wetherby | 2018 |
| Augean LFT Claims Co Limited | Wetherby | 2020 |
| Augean Property Limited | Wetherby | 1999 |
| Augers Limited | Maldon | 1981 |
| Aughnahoory Farms Ltd | Newry | 2018 |
| Auglass Limited | Suffolk | 2002 |
| Augmatic Ltd | Bury St. Edmunds | 2024 |
| Augurship Trustee Company Limited | London | 2003 |
| August (GBR) PTY Ltd | Sale | 2017 |
| August Motors Limited | Hampshire | 1973 |
| Augustcopy Limited | London | 2020 |
| Augustus College Ltd | London | 2017 |
| Augustus Consulting Ltd | London | 2025 |
| Auker Hutton Limited | Tunbridge Wells | 2019 |
| Aukett Fitzroy Robinson Europe Limited | London | 2005 |
| Aukett Fitzroy Robinson Limited | London | 2013 |
| Aukett Group Limited | London | 2005 |
| Aukett Limited | London | 2005 |