| Alpha Care Management Services Limited | Health & social care | 2005 |
| Alpha Care Management Services NO.3 Limited | Health & social care | 2015 |
| Alphasauce Limited | Wholesale & retail | 2018 |
| Altech Telecom Fire and Security Group Ltd | Administrative & support | 2016 |
| Altwood Bespoke Ltd | Manufacturing | 2018 |
| Alvil Transport Ltd | Transport & logistics | 2025 |
| Amaira-London Limited | Wholesale & retail | 2016 |
| Amber Builders Limited | Construction | 1996 |
| Amberley House Care Limited | Extraterritorial | 2014 |
| Amdecuk Limited | Real estate | 2018 |
| Amicura Birmingham Limited | Health & social care | 2023 |
| Amicura Care Group Limited | Financial services | 2026 |
| Amicura Care Homes Limited | Health & social care | 2026 |
| Amicura Chorley Limited | Health & social care | 2014 |
| Amicura Edinburgh Limited | Health & social care | 2021 |
| Amicura Glasgow Limited | Health & social care | 2021 |
| Amicura Haslingden Limited | Health & social care | 2015 |
| Amicura Holdings Limited | Financial services | 2018 |
| Amicura Kettering Limited | Health & social care | 2018 |
| Amicura Lancashire Limited | Health & social care | 2025 |
| Amicura Limited | Health & social care | 2011 |
| Amicura Morecambe Limited | Health & social care | 2018 |
| Amicura Redruth Limited | Health & social care | 2020 |
| Amicura Services Limited | Health & social care | 2020 |
| Amitore Homes Limited | Real estate | 2025 |
| Amiwigs Ltd | Other services | 2011 |
| Ammazzi Ltd | Manufacturing | 2021 |
| Ample Power and Light Ltd | Construction | 2018 |
| Amplifi Communications Limited | Professional & scientific | 2023 |
| Amps Properties Limited | Construction | 2016 |
| ANA WIZ Limited | Wholesale & retail | 2004 |
| Anchovy Consulting Ltd | Real estate | 2017 |
| AND Dance Limited | Other services | 2025 |
| Anglo Swiss Limited | Extraterritorial | 1999 |
| Anglo-European Software Limited | Wholesale & retail | 1991 |
| Animals at Home (North Surrey) Limited | Professional & scientific | 2019 |
| ANN Mansfield Recruitment Ltd | Administrative & support | 2019 |
| Anna Moody’S Grooming Salon Ltd | Professional & scientific | 2024 |
| Another Nice View Ltd | Agriculture & fishing | 2025 |
| Ansom Moore Limited | Wholesale & retail | 1997 |
| ANT Construction Ltd | Construction | 2012 |
| Anthony G Harrison Ltd | Professional & scientific | 2024 |
| Anthony Property Investement Ltd | Real estate | 2025 |
| Antill Properties Ltd. | Real estate | 1981 |
| Antoni Food Ltd | Hospitality | 2019 |
| Anuraag Badola Ltd | Other services | 2022 |
| AP Elec Services Ltd | Construction | 2015 |
| Apeiro Property Investment Ltd | Real estate | 2023 |
| Apex Build Systems Limited | Information & communication | 2026 |
| Apex Stoneworks Solutions Ltd | Manufacturing | 2025 |
| APM Tech Solutions Limited | Professional & scientific | 2025 |
| Approved Electric Services Ltd | Construction | 2021 |
| AR Phoenix Ltd | Wholesale & retail | 2025 |
| Araja Limited | Hospitality | 2023 |
| Arboreta Tree Services Limited | Administrative & support | 2026 |
| Archer's Decorating Limited | Construction | 2013 |
| Arden Oaks Resident Management Company Limited | Professional & scientific | 2025 |
| Arek Build & Renovations Limited | Construction | 2011 |
| ARI Shine Ltd | Administrative & support | 2025 |
| ARIES1964 Limited | Financial services | 2026 |
| Arlindi Construction Ltd | Construction | 2018 |
| Armadillo Furniture Limited | Wholesale & retail | 2007 |
| ARR Grounds Work Ltd | Construction | 2022 |
| Arsal Ltd | Wholesale & retail | 2026 |
| Arthur Development Ltd | Construction | 2020 |
| Aryana Lashes Limited | Wholesale & retail | 2025 |
| Asatoma Construction Ltd | Construction | 2025 |
| ASH Builders UK Limited | Construction | 2006 |
| ASH Vale Kebab House Limited | Hospitality | 2017 |
| Ashcom Electronics Limited | Wholesale & retail | 2002 |
| Ashfronts Bespoke Homes Ltd | Construction | 2022 |
| Ashgrove Residential Care Limited | Health & social care | 2022 |
| Ashley Construction Southern Limited | Construction | 1976 |
| ASHLEY221 Limited | Construction | 2015 |
| Ashwood & Cedarwood Limited | Real estate | 2024 |
| ASL Assets Ltd | Real estate | 2026 |
| Aspen and Wood Limited | Hospitality | 2024 |
| Aspen Grange (Stowmarket) Management Company Limited | Professional & scientific | 2022 |
| Aspen Overseas Ltd | Professional & scientific | 2022 |
| ASR Future Ltd | Professional & scientific | 2025 |
| Assessment Centre Limited(The) | Extraterritorial | 1986 |
| Asta Grosvenor Limited | Real estate | 1969 |
| Astellas Pharma Europe Ltd. | Wholesale & retail | 1990 |
| Astellas Pharma Ltd. | Wholesale & retail | 1964 |
| AT42 Ltd | Wholesale & retail | 2017 |
| Atacama Europe Asset Management Ltd | Real estate | 2015 |
| Atlantic Arts Agency Limited | Wholesale & retail | 2022 |
| Atwal Corporation Limited | Real estate | 2007 |
| Auctionone Limited | Real estate | 2024 |
| Authently Consulting Limited | Professional & scientific | 2024 |
| AVC Health Ltd | Financial services | 2024 |
| Aventino Ltd | Hospitality | 2026 |
| Aventurine Therapies Ltd | Professional & scientific | 2020 |
| AVH Capital Limited | Financial services | 2014 |
| AVI Tech Solutions Ltd | Wholesale & retail | 2024 |
| Aviation Construction Consultancy Limited | Construction | 2018 |
| Avingstone Investments Limited | Financial services | 2015 |
| Avington Capital Partners Limited | Extraterritorial | 2005 |
| Avington International Limited | Extraterritorial | 2005 |
| Avington Management Services Limited | Extraterritorial | 2005 |