| Archutha Ltd | Health & social care | 2020 |
| Ardeja Trading Limited | Wholesale & retail | 2011 |
| Ardour London Ltd | Arts & recreation | 2018 |
| Arete Travel Ltd | Administrative & support | 2010 |
| Arhan Thai UK Limited | Hospitality | 2024 |
| Ariadne Private Clients Limited | Professional & scientific | 2016 |
| Arihant Limited | Real estate | 1997 |
| Arivo Concept Ltd | Transport & logistics | 2010 |
| Arixa Connect Ltd | Wholesale & retail | 2026 |
| Arjun Ventures Limited | Information & communication | 2017 |
| ARK Care Alliance Limited | Health & social care | 2025 |
| ARK Infotech Ltd | Information & communication | 2024 |
| ARK Smart Homes Limited | Construction | 2026 |
| ARK Ultrasound Diagnostics Limited | Health & social care | 2025 |
| Arkash Management Consultants Limited | Health & social care | 2012 |
| Arkley Grounds Maintenance Ltd | Administrative & support | 2024 |
| Arlan Capital Ltd | Financial services | 2023 |
| Arma Properties UK Limited | Real estate | 2014 |
| Army Housing Ltd | Real estate | 2012 |
| Arnica Ltd | Health & social care | 2015 |
| Arnico Group Ltd | Construction | 2026 |
| Arosco Limited | Professional & scientific | 2016 |
| Arpiem Limited | Health & social care | 2023 |
| Arrk Investments Ltd | Households | 2021 |
| Artewedes Limited | Professional & scientific | 2024 |
| Artset International Limited | Wholesale & retail | 2012 |
| Arunanav Limited | Health & social care | 2021 |
| Arvilia Ltd | Wholesale & retail | 2020 |
| Arvitus Ltd | Professional & scientific | 2014 |
| Arya and Advay Limited | Information & communication | 2024 |
| AS Education Ltd | Education | 2019 |
| Asca Intelligence Limited | Information & communication | 2025 |
| Asdac Consulting Ltd | Professional & scientific | 2020 |
| ASH Tree Services Ltd | Other services | 2017 |
| Asharafali Limited | Health & social care | 2024 |
| Ashbourne Square Residents Management Limited | Households | 1991 |
| Ashgov Karma Ltd | Information & communication | 2019 |
| Ashley Industrial Properties Limited | Real estate | 2010 |
| Ashley Range Contractors Limited | Construction | 2002 |
| Ashurst Close (Flats) Limited | Households | 1972 |
| Ashwin Brothers & Co Limited | Professional & scientific | 2012 |
| ASK Logic Ltd | Information & communication | 2013 |
| Asmk Consulting Limited | Information & communication | 2019 |
| Asmk Holding Ltd | Real estate | 2019 |
| Aspen Projects Ltd | Construction | 2025 |
| Assembly of Creative Arts C.I.C. | Arts & recreation | 2014 |
| Assesslens Limited | Information & communication | 2024 |
| Asset Securities London Ltd | Real estate | 2024 |
| Assure Property Limited | Real estate | 2004 |
| Asteria Designs Limited | Professional & scientific | 2021 |
| Astons Investments LLP | | 2013 |
| Astra Events Limited | Administrative & support | 2023 |
| AT Develop Ltd | Real estate | 2022 |
| Ateam Ventures Ltd | Real estate | 2017 |
| Athena Residents Limited | Professional & scientific | 2016 |
| Atlas Osteopathy Ltd | Health & social care | 2014 |
| Atomcove Enterprises Limited | Real estate | 1998 |
| Attacked.Ai Ltd | Information & communication | 2024 |
| Audiology Central Limited | Health & social care | 2018 |
| Audit and Risk Advisors Ltd | Administrative & support | 2011 |
| AUM MAA AUM Limited | Professional & scientific | 2018 |
| AUM MAA AUM Properties Limited | Real estate | 2018 |
| Aumnik Ltd | Manufacturing | 2018 |
| Aura Gems Ltd | Manufacturing | 2025 |
| Auraelius Ltd | Other services | 2011 |
| Aurah Aesthetics UK Limited | Other services | 2025 |
| Aureon Nest Ltd | Real estate | 2026 |
| Aurient International Limited | Real estate | 2024 |
| Aurion Consulting Limited | Information & communication | 2025 |
| Aurora Capital Partners Consultancy Ltd | Professional & scientific | 2025 |
| Austin Holland Limited | Administrative & support | 2013 |
| Autentico Ltd | Hospitality | 2014 |
| Automotive Management Systems Limited | Wholesale & retail | 2003 |
| AVA Assets Limited | Real estate | 2020 |
| Avam Investment (Residential) Limited | Real estate | 2026 |
| Avam Investment Limited | Real estate | 2023 |
| Avantis Hotels Limited | Hospitality | 2001 |
| Avantis Piccadilly Limited | Hospitality | 2017 |
| Avantis York Limited | Hospitality | 2011 |
| Aventix Limited | Real estate | 2020 |
| AVH Northwood Limited | Real estate | 2020 |
| Avhh Limited | Financial services | 2021 |
| Aviator Motors Ltd | Wholesale & retail | 2022 |
| Avicenna Group Ltd | Education | 2024 |
| Avigyan Apparel UK Ltd | Wholesale & retail | 2018 |
| Avikin Limited | Real estate | 2025 |
| Avisford Park Hotel Limited | Hospitality | 2021 |
| Avonix Limited | Real estate | 2018 |
| AW Advisors Limited | Financial services | 2019 |
| Awaba Properties Limited | Real estate | 2020 |
| AX Capitol Ltd | Agriculture & fishing | 2021 |
| Axiom Wealth Management Limited | Financial services | 1999 |
| Ayodhya Investments Ltd | Financial services | 2026 |
| AYS London Ltd | Wholesale & retail | 2017 |
| Azine Properties Limited | Real estate | 2013 |
| Azmera Limited | Real estate | 2019 |
| Azna Holdings Ltd | Professional & scientific | 2025 |
| B P Viner Consultancy Services Ltd | Administrative & support | 2017 |
| B R P Assets Ltd | Real estate | 2019 |
| B Spark Flow Ltd | Construction | 2026 |