| Amcoal Limited | Brecon | 1996 |
| AMD Energy Limited | Lancaster | 2024 |
| Amds Berkshire Ltd | Reading | 2025 |
| AME East Africa Limited | London | 2013 |
| Amec Foster Wheeler International Limited | Knutsford | 1996 |
| Amedex Limited | Willerby | 2019 |
| America's Pink Salt Ltd | London | 2020 |
| American Agravis Co., Ltd | Cardiff | 2026 |
| Amerisur Resources Limited | Salford | 2000 |
| AMG Commissioning Services Ltd | Renfrew | 2021 |
| Aminex Petroleum Services Ltd. | London | 1986 |
| Amir (UK) Properties Limited | Invergarry | 2010 |
| Amoco (Fiddich) Limited | Liverpool | 1971 |
| Amoco U.K.Petroleum Limited | Middlesex | 1964 |
| Amos (Aberdeen) Ltd | Ellon | 2018 |
| Amossco Holdings Limited | London | 2000 |
| Amossco Limited | London | 1994 |
| Amossco ODS Limited | London | 1960 |
| Ampco Metal Limited | Coventry | 1970 |
| Amphi Capital Limited | Axminster | 2018 |
| Amplus Energy (Holdings) Limited | Aberdeen | 2016 |
| Amplus Energy Services Limited | Aberdeen | 2008 |
| AMR Consultancy Services Limited | Ruislip | 2014 |
| Amron (SA) Co., Ltd | Cambridge | 2026 |
| Amsp Limited | Laurencekirk | 2024 |
| Amtech Project Solutions Ltd | London | 2013 |
| AMV Equity Investments Limited | Bracknell | 2015 |
| Anapco Ltd | London | 2023 |
| Ancaster Copper Hill Stone Limited | Grantham | 2004 |
| Anchor Line Limited | London | 1996 |
| Anchor Point Access Ltd | Aberdeen | 2026 |
| Andaluz Access Ltd | Innerleithen | 2009 |
| Andas Consulting Limited | Leatherhead | 2021 |
| Andola Logistics Ltd | Peterhead | 2012 |
| Andrei Mobile Welding Ltd | Northampton | 2025 |
| Andrew Buchan Ltd | Peterhead | 2013 |
| Andrew Douglas Associates Limited | Turriff | 2006 |
| Andrew Morton | London | 1998 |
| Andrew Ogilvie & Partners Ltd | Inverurie | 2015 |
| Andrew Younger Ltd | Edinburgh | 2023 |
| Andro-Flex Limited | Shepperton | 2018 |
| Andromeda Capital Investments UK Ltd | Hove | 2018 |
| Anfield Energy Limited | Gardenstown | 2023 |
| Angkal Property Limited | Glasgow | 2022 |
| Angle Park Sand and Gravel Company Limited | Fife | 1978 |
| Anglesey Masonry Ltd. | Anglesey | 2003 |
| Anglesey Mining PLC | Amlwch | 1984 |
| Anglia Crushing & Screening Ltd | Peterborough | 2022 |
| Anglian Excavations Limited | Ipswich | 2002 |
| Anglo Africa Corporation Limited | Kingston-Upon-Thames | 2008 |
| Anglo African Services Ltd | London | 2019 |
| Anglo African Solutions Limited | London | 2016 |
| Anglo American Crop Nutrients Holdings Limited | London | 2012 |
| Anglo American Crop Nutrients Limited | London | 2003 |
| Anglo American PLC | London | 1998 |
| Anglo American Woodsmith (Teesside) Limited | London | 2012 |
| Anglo American Woodsmith Limited | London | 2010 |
| Anglo Arab Morocco Gold Capital Ltd | London | 2026 |
| Anglo Asian Mining PLC | London | 2004 |
| Anglo Asian Operations Limited | London | 2004 |
| Anglo Canadian Exploration (Ace) Limited | Anglesey | 1973 |
| Anglo Earth Resourcing Ltd | Daventry | 1996 |
| Anglo Indonesian Mining Limited | Coventry | 2005 |
| Anglo OIL Corporation Limited | London | 2007 |
| Anglo Rajhi Engineering Co (UK) Limited | London | 2011 |
| Anglo Tanzania Gold Limited | London | 2004 |
| Anglo Zimbabwe Mining Ltd | Henfield | 2023 |
| Anglo-American Exploration Co. Limited | Bristol | 1980 |
| Angola LNG Marketing Ltd | London | 2012 |
| Angus Energy PLC | London | 2015 |
| Angus Energy Weald Basin NO.3 Limited | Edinburgh | 1974 |
| Angus Macarthur Limited | Isle Of Lewis | 2021 |
| Angus Mackenzie Consulting Ltd | Sandwich | 2023 |
| Anham Industries Limited | Gloucester | 2012 |
| Animus Technology Limited | Inverurie | 2014 |
| Anisor Enterprises Ltd | London | 2021 |
| Annett Sand & Gravel Ltd | Newry | 2003 |
| Anog Energy Limited | Colchester | 2015 |
| ANS Energy Ventures Limited | Aberdeen | 2003 |
| Anson Site Services Ltd | Rowley Regis | 2022 |
| Ansong Askew Ltd | Liverpool | 2020 |
| Antech Energy Services Limited | Exeter | 2025 |
| Antech Holdings Ltd | Exeter | 2019 |
| Antech Limited | Exeter | 1994 |
| Antech Oilfield Services Ltd | Exeter | 2019 |
| Anthony Barton Offshore Services Ltd | Liverpool | 2025 |
| Antofagasta PLC | London | 1982 |
| Antolini Stone Gallery Limited | London | 2025 |
| ANU Advisory Ltd | London | 2026 |
| Anzcorp Securities Limited | Cardiff | 2020 |
| AO Investment Group Limited | West Malling | 2024 |
| Aobx Agrifluids Ltd. | London | 2025 |
| Aoraki Designs Ltd | Inverurie | 2017 |
| AOT International Ltd | London | 2016 |
| AOT Manufacturing Ltd | London | 2020 |
| AP GEO Services Ltd | London | 2026 |
| AP Lifting Services Ltd | Great Yarmouth | 2018 |
| Apache North Sea Limited | | 2002 |
| Apex Access-Electrical Solutions Ltd | Thornton-Cleveleys | 2016 |
| Apex Global Commerce Limited | Cambridge | 2025 |