| Arion Consulting Limited | Information & communication | 2026 |
| Aristodax Ltd | Information & communication | 2016 |
| ARJ Forwarding Ltd | Transport & logistics | 2017 |
| ARJ Property Ventures Ltd | Construction | 2026 |
| ARK Wrought-Ironwork Ltd | Manufacturing | 2003 |
| Arkman Software Limited | Information & communication | 2022 |
| Arlo Managed Services Ltd | Professional & scientific | 2025 |
| ARM Logics Ltd. | Information & communication | 2014 |
| Armitage Associates Limited | Information & communication | 2006 |
| Armitage Place Management Company Limited | Real estate | 2007 |
| Armonia Collective Ltd | Public administration | 2025 |
| Armourco Sports Ltd | Wholesale & retail | 2021 |
| Arms and Hive Pubs Ltd | Hospitality | 2025 |
| Armstrong Bell Accountancy Limited | Professional & scientific | 2012 |
| Arnold Cook (Graphic Arts) Limited | Wholesale & retail | 1979 |
| Arorra Express Ltd | Wholesale & retail | 2025 |
| Arpaiu Consulting Limited | Professional & scientific | 2020 |
| Arpik Trans Ltd | Transport & logistics | 2017 |
| ARS Motors UK Ltd | Wholesale & retail | 2025 |
| Arsh Real Estate Ltd | Real estate | 2023 |
| Art & Craft Video Ltd | Information & communication | 2022 |
| Art Alert Limited | Wholesale & retail | 2015 |
| Art Flooring Services Ltd | Construction | 2023 |
| Art for OUR Planet Limited | Wholesale & retail | 2024 |
| Art of Manipulation Limited | Other services | 2023 |
| Art of Talent Limited | Other services | 2007 |
| Arthaus Visual Communications Ltd | Professional & scientific | 2023 |
| Artisan Frames Limited | Manufacturing | 2012 |
| Artistry Limited | Wholesale & retail | 2008 |
| Artmim Limited | Real estate | 2013 |
| Arvon House Management Company Limited | Households | 1987 |
| Arxis Consulting Ltd | Professional & scientific | 2025 |
| ARY Properties PK Ltd | Real estate | 2019 |
| Arya SON Properties Limited | Real estate | 2020 |
| AS Legal Limited | Professional & scientific | 2019 |
| AS Medi-Locum Ltd | Health & social care | 2022 |
| As&P Consulting Ltd | Other services | 2018 |
| ASA Elite Ltd | Real estate | 2023 |
| Asali Studios Ltd | Information & communication | 2025 |
| ASB Consulting Services Ltd | Professional & scientific | 2021 |
| Asbitrad Limited | Wholesale & retail | 2020 |
| Asbiverse Limited | Professional & scientific | 2022 |
| Ascendancy Partnership Trust | Education | 2023 |
| Ascot Building & Interiors Limited | Construction | 2007 |
| Ascot College of Electrical Studies Limited | Education | 2010 |
| Ascot Plumbing & Heating Services Ltd | Construction | 2004 |
| Ascot Swim School (Cavan) Limited | Arts & recreation | 2016 |
| Ascot Swim School (K&A) Limited | Arts & recreation | 2016 |
| Ascot Wood Place Management Company Limited | Households | 1994 |
| Asees Capital Limited | Financial services | 2026 |
| Asgeria Associates Ltd | Health & social care | 2017 |
| ASH Production Designs Ltd | Information & communication | 2025 |
| ASH Property Professionals Ltd | Real estate | 2023 |
| Ashford Fitness Consultancy Ltd | Other services | 2021 |
| Ashjo Property Ltd | Real estate | 2017 |
| Ashley Court Limited | Real estate | 1989 |
| Ashmill Limited | Administrative & support | 2000 |
| Ashridge Communications Limited | Information & communication | 2002 |
| Ashworth Financial Services Ltd | Financial services | 2010 |
| Asian Cuisine Group Limited | Hospitality | 2022 |
| Asili Aesthetics Ltd | Health & social care | 2025 |
| Askeri Limited | Transport & logistics | 2020 |
| ASL Global Logistics Limited | Transport & logistics | 2024 |
| Asli Trading Limited | Wholesale & retail | 2022 |
| Aspects Language Solutions Limited | Professional & scientific | 2025 |
| Aspen Place (Maidenhead) Management Company Limited | Administrative & support | 2008 |
| Asperitas Solutions Limited | Professional & scientific | 2019 |
| Aspire Consultancy Group Ltd | Professional & scientific | 2012 |
| Aspire Investments Group Limited | Real estate | 2020 |
| ASR Property Solutions Ltd | Real estate | 2015 |
| Asset Holding Company (AHC) Ltd | Real estate | 2011 |
| Assiduous Value Investments Limited | Real estate | 2015 |
| AST UK Holdings Ltd | Financial services | 2022 |
| Astoleio Limited | Professional & scientific | 2024 |
| Aston Accountants & Tax Consultants Ltd | Professional & scientific | 2013 |
| Aston Lynch Building Supplies Ltd | Manufacturing | 2017 |
| Astra World Ltd | Information & communication | 2023 |
| Astria Ltd | Information & communication | 2025 |
| Astro Clean Limited | Administrative & support | 2019 |
| Astrocom Limited | Information & communication | 2002 |
| Asuene Europe Limited | Information & communication | 2025 |
| AT Liberty Ltd | Professional & scientific | 2001 |
| AT the Estuary Ltd | Education | 2025 |
| Atca Limited | Professional & scientific | 2013 |
| ATD Building Services Limited | Construction | 2004 |
| ATD Property Maintenance Limited | Extraterritorial | 2009 |
| Aten Europe Limited | Financial services | 2006 |
| Aten UK Limited | Manufacturing | 2006 |
| ATG Luxuries Limited | Other services | 2024 |
| ATG Luxx Ltd | Other services | 2026 |
| Athena Angels Gymnastics Club Limited | Education | 2019 |
| Athena Consulting Partners & Ventures Limited | Information & communication | 2022 |
| Athena One Limited | Construction | 2011 |
| Atkin Research & Development Limited | Information & communication | 1994 |
| Atlantic Precision Strategies Ltd | Other services | 2025 |
| Atlast a Green Future Limited | Extraterritorial | 2021 |
| Attachments Italia Limited | Wholesale & retail | 2024 |
| Attendance for YOU Limited | Health & social care | 2026 |
| Attendflower Limited | Professional & scientific | 1995 |
| Atticus Line Limited | Manufacturing | 2024 |