| AP2L 2407 Dobby Rocks Energy Storage Ltd | Energy | 2024 |
| Apex Arch Constructors Ltd | Construction | 2026 |
| Apex International Holdings Limited | Financial services | 2024 |
| APM Global Real Estate Limited | Real estate | 2025 |
| APO Global Limited | Information & communication | 2025 |
| Apollemis Properties Limited | Construction | 2021 |
| Apollo Data Solutions Ltd | Other services | 2022 |
| Appetiser Ltd | Information & communication | 2017 |
| Applecare Limited | Health & social care | 2025 |
| Approach Aviation Flight Services Limited | Transport & logistics | 2018 |
| Apsley Group International Ltd | Professional & scientific | 2013 |
| APW Financial Investments Limited | Real estate | 2021 |
| APX Projects Ltd | Professional & scientific | 2016 |
| AQ Construction Services Limited | Construction | 2012 |
| Aquadulce Ltd | Professional & scientific | 2018 |
| Aquariid Ltd | Information & communication | 2021 |
| ARC M1 Ltd | Financial services | 2026 |
| ARC Project Management Consultancy Limited | Professional & scientific | 2011 |
| Arca Industries Limited | Manufacturing | 2013 |
| Archangel Consultants Limited | Other services | 2022 |
| Archangel Estates Limited | Financial services | 2014 |
| Archangel Properties Limited | Real estate | 2002 |
| Archer Sports Management Ltd | Other services | 2015 |
| Archieg Capital Limited | Financial services | 2025 |
| Archplan Projects Limited | Professional & scientific | 2006 |
| Archvex Developments Ltd | Real estate | 2026 |
| Archway Capital Partners Limited | Financial services | 2020 |
| Arcos Investments Limited | Construction | 2022 |
| Arctic Cooling Services Limited | Energy | 2016 |
| Arctic Fire Limited | Public administration | 2025 |
| Arctic Glazing Limited | Construction | 2026 |
| Arctic Group Holdings Limited | Financial services | 2025 |
| Arctic Property Group Ltd | Real estate | 2022 |
| Ardcastle Developments Ltd | Financial services | 2025 |
| Ardent Land Limited | Real estate | 2020 |
| Arena Performance Ltd | Professional & scientific | 2024 |
| Arepa Junction Ltd | Hospitality | 2024 |
| Arevalo Investments Ltd | Professional & scientific | 2011 |
| ARH International Financial Consulting Ltd | Financial services | 2018 |
| ARH123 Limited | Administrative & support | 1991 |
| Arichie Trading Limited | Administrative & support | 2010 |
| Arida | Education | 2024 |
| ARJ Entertainment Limited | Administrative & support | 2021 |
| ARK Collections Ltd | Wholesale & retail | 2026 |
| ARK Nangle Consulting Ltd | Professional & scientific | 2021 |
| Arlo Capital Ltd | Financial services | 2025 |
| Arnold Hall Ltd | Construction | 2025 |
| Aromafutures Ltd | Wholesale & retail | 2015 |
| Arundel Group Limited | Financial services | 1992 |
| Ascendant TV Ltd | Professional & scientific | 2024 |
| Ascert Limited | Information & communication | 1997 |
| Ascot Associates Chimney Services Limited | Construction | 2002 |
| Asendia UK Limited | Transport & logistics | 2004 |
| ASH Property Partners Limited | Real estate | 2025 |
| ASH Transport Service Limited | Transport & logistics | 2016 |
| Ashdene Projects Limited | Construction | 2015 |
| Ashdown Accountancy Limited | Professional & scientific | 2005 |
| Ashdown Group Limited | Administrative & support | 1999 |
| Ashdown Holdings Ltd | Financial services | 2019 |
| Ashdown I.T. Limited | Professional & scientific | 2005 |
| Ashley Holdings Limited | Real estate | 2025 |
| Ashley Rose Properties Limited | Real estate | 2021 |
| Ashwood Electrical Limited | Construction | 2014 |
| Asian Alchemy Limited | Professional & scientific | 2015 |
| ASK Marketing Ltd | Professional & scientific | 2026 |
| ASL Lifts Ltd | Construction | 2012 |
| ASM IT Services Ltd | Information & communication | 2024 |
| Aspect Systems Limited | Administrative & support | 2005 |
| Aspen House Interiors Ltd | Professional & scientific | 2024 |
| Aspi BTL Ltd | Real estate | 2017 |
| Aspi Developments Ltd | Real estate | 2019 |
| Aspi Homes BTL Ltd | Real estate | 2024 |
| Aspi Homes Group Ltd | Real estate | 2013 |
| Aspi Homes Surrey Ltd | Real estate | 2021 |
| Aspi Property Limited | Real estate | 2018 |
| Aspinalls Family Office LLP | | 2009 |
| Aspiro AI Limited | Professional & scientific | 2025 |
| Aspreys Accountants Ltd | Professional & scientific | 2017 |
| Aspreys Business Consultants Ltd | Professional & scientific | 2020 |
| Aspreys Commercial Finance Ltd | Professional & scientific | 2020 |
| Asset Security Construction Ltd | Wholesale & retail | 2008 |
| Associated Recordings Company Ltd | Information & communication | 2014 |
| Assure Property Developments Ltd | Construction | 2021 |
| Assured Property Care Limited | Households | 2025 |
| Astarbox Ltd | Manufacturing | 2024 |
| Astindale Bidborough Limited | Construction | 2014 |
| Astindale Developments Limited | Construction | 2016 |
| Astindale Home Farm Limited | Construction | 2014 |
| Astindale London Road Limited | Construction | 2015 |
| Astindale Mount Harry Road Limited | Real estate | 2019 |
| Astindale Woodbridge (2020) Limited | Construction | 2020 |
| Astindale Woodbridge Limited | Construction | 2015 |
| Aston Mead Land & Planning Ltd | Real estate | 2015 |
| Astra Smart Development & Innovation Limited | Professional & scientific | 2013 |
| AT the Double Limited | Information & communication | 2021 |
| AT4 Carpentry Ltd | Manufacturing | 2019 |
| ATB Services Ltd | Administrative & support | 2017 |
| Atek Accounting Solutions Limited | Professional & scientific | 2012 |
| Atek Brooklands Limited | Professional & scientific | 2020 |
| Atelier Limited | Arts & recreation | 2019 |