| ARC Rail Limited | Administrative & support | 2013 |
| Arcata Projects Limited | Construction | 2021 |
| Archer GAS and Heating Services Limited | Construction | 2013 |
| Archies Constructions Limited | Construction | 2026 |
| Archmagic Limited | Financial services | 1987 |
| Ares UK Limited | Real estate | 2020 |
| Arete Ventures Group Ltd | Administrative & support | 2013 |
| Areté Ashcroft Limited | Administrative & support | 2026 |
| Argentum Bespoke Estates Limited | Real estate | 2012 |
| Argyll Properties Limited | Real estate | 2023 |
| ARH Ophthalmic Solutions Ltd | Health & social care | 2022 |
| Aria Tech Global Limited | Information & communication | 2025 |
| Arianne Court Management Limited | Households | 1995 |
| Arion Financial Limited | Manufacturing | 2007 |
| Arise and Excel | Public administration | 2012 |
| Arise Recruitment Agency Limited | Extraterritorial | 2021 |
| ARK Developments (London) Ltd | Construction | 2017 |
| Arlbid Properties Ltd | Real estate | 2021 |
| Arrow Holdings Kent Limited | Arts & recreation | 2020 |
| Arsh Ventures Limited | Wholesale & retail | 2019 |
| Art & Craft Valley Limited | Wholesale & retail | 2002 |
| Arta Residents Management Company Limited | Households | 2007 |
| Arterial Hub LLP | | 2003 |
| Arts Bar, David Lean Cinema, Croydon CIC | Hospitality | 2019 |
| Arts Centre Guildford Ltd | Education | 2022 |
| Arun RAM & Co Ltd | Wholesale & retail | 2019 |
| Aruna BLU Limited | Wholesale & retail | 2014 |
| Aruna Enterprises Ltd | Real estate | 2025 |
| Aruna London Ltd | Wholesale & retail | 2018 |
| ARUNI4 Limited | Health & social care | 2024 |
| As&Jh Property Limited | Real estate | 2025 |
| As-Msr-Engineering Ltd | Professional & scientific | 2014 |
| ASC Coachworks Ltd | Wholesale & retail | 2011 |
| Ascent Fostering Agency Limited | Health & social care | 2012 |
| Ascot International Footwear Limited | Wholesale & retail | 2008 |
| Ascot International Sports & Footwear Limited | Wholesale & retail | 2008 |
| Ascot TM Limited | Real estate | 2008 |
| ASH & DI Group Ltd | Other services | 2018 |
| ASH Beauty and Hair Limited | Other services | 2025 |
| ASH Bird Ltd | Wholesale & retail | 2020 |
| ASH James & Associates Limited | Financial services | 2012 |
| Ashby and Partners LLP | | 2015 |
| Ashelm Limited | Information & communication | 2017 |
| Ashmaan Limited | Transport & logistics | 2010 |
| Ashraya Homes Ltd | Real estate | 2023 |
| Ashton Architecture Limited | Professional & scientific | 2017 |
| Ashton Financial Consulting Ltd | Financial services | 2021 |
| Ashton Paul Ltd. | Professional & scientific | 2011 |
| Ashurst Lodge Healthcare Limited | Health & social care | 2018 |
| Ashwood Park Management Company Limited | Households | 1988 |
| Asia Properties Ltd | Real estate | 2021 |
| Asian Catering Federation | Other services | 2012 |
| Asian Curry Awards Event Ltd | Health & social care | 2025 |
| Asian Curry Awards Limited | Health & social care | 2008 |
| Asian Curry Club Limited | Extraterritorial | 2013 |
| ASK-4-IT Solutions Ltd | Information & communication | 2024 |
| Aslg Properties Ltd | Real estate | 2019 |
| Asling Investment Ltd | Extraterritorial | 2010 |
| ASP Properties 1 Limited | Real estate | 2022 |
| Aspirant League Ltd | Education | 2024 |
| Aspire Masonry Limited | Construction | 2012 |
| Aspire Security Limited | Administrative & support | 2014 |
| Aspyre Corporation Ltd | Real estate | 2023 |
| Asra Fudco Limited | Wholesale & retail | 2022 |
| Associated Laboratories Limited | Manufacturing | 2004 |
| Association of Processing and Packaging Professionals Ltd | Professional & scientific | 2005 |
| Assurestack Solutions Limited | Information & communication | 2023 |
| Astir Cars Ltd | Transport & logistics | 2024 |
| Astir Chauffeurs Ltd | Transport & logistics | 2022 |
| Astonishing One Ltd | Wholesale & retail | 2024 |
| Astron Health Ltd | Health & social care | 2024 |
| Astutebuild Projects Ltd | Construction | 2023 |
| At&D Properties Ltd | Real estate | 2021 |
| Atis Solutions Limited | Information & communication | 2017 |
| Atlas 110 Limited | Extraterritorial | 2024 |
| Atom Investment London Ltd | Wholesale & retail | 2020 |
| ATR Surrey Ltd | Hospitality | 2017 |
| ATS Automated Training Systems Ltd | Information & communication | 1999 |
| ATS Contracts Ltd. | Construction | 2011 |
| Atsu Properties Ltd | Real estate | 2024 |
| Attuned Incorporated Limited | Health & social care | 2017 |
| Auction ANY Property Ltd | Real estate | 2026 |
| Audacious Pizza Limited | Hospitality | 2023 |
| Aura Infotech Ltd | Information & communication | 2018 |
| Aurision Limited | Wholesale & retail | 2026 |
| Australian Football League England Ltd | Arts & recreation | 2010 |
| Automation UK (Events) Limited | Administrative & support | 2022 |
| Automation UK Ltd | Other services | 2023 |
| AV Badminton Club Ltd | Arts & recreation | 2024 |
| Aventis Digtech Limited | Information & communication | 2025 |
| Avenue Mortgage Solutions Ltd | Financial services | 2017 |
| AVI Kinds Investment Ltd | Real estate | 2021 |
| AVI Kinds Ltd | Wholesale & retail | 2019 |
| Avoca Holdings Limited | Financial services | 2016 |
| Avoca Vibes Limited | Wholesale & retail | 2025 |
| Avoprocure Ltd | Wholesale & retail | 2015 |
| Avreem Ltd | Real estate | 2023 |
| Awans Investments Limited | Real estate | 2018 |
| AWM SP Limited | Administrative & support | 2021 |
| Axigral Ltd | Information & communication | 2006 |