| Armstrong Engineering Consultants Limited | Information & communication | 2015 |
| Arqmind Ltd | Information & communication | 2019 |
| Arri Monk Ltd | Professional & scientific | 2002 |
| Arshaarna Homes Ltd | Real estate | 2015 |
| Art NOT Customs Limited | Arts & recreation | 2017 |
| Artavia Limited | Manufacturing | 2016 |
| Artemis Medical Limited | Professional & scientific | 2025 |
| Artinsite Limited | Construction | 2003 |
| Artisan Engineering Limited | Professional & scientific | 2018 |
| Artisan Table Limited | Hospitality | 2024 |
| AS RAI Management Limited | Administrative & support | 2021 |
| Asad Creation Ltd | Wholesale & retail | 2026 |
| ASBESTOS365 Limited | Professional & scientific | 2021 |
| ASC Construction Limited | Construction | 2026 |
| Ascender Limited | Information & communication | 2022 |
| Ascending Health & Fitness Limited | Arts & recreation | 2024 |
| Ascot Support Services Limited | Financial services | 2023 |
| Ascott Property Group Ltd | Real estate | 2024 |
| Asftech Limited | Other services | 2020 |
| Asgard Holdings Limited | Administrative & support | 2016 |
| ASH Grove Living Limited | Real estate | 2019 |
| ASH Perspective Ltd | Education | 2024 |
| Asha Property Holdings Limited | Real estate | 2026 |
| Ashcroft & Cameron Limited | Administrative & support | 2017 |
| Ashcroft Property Holdings Limited | Real estate | 2016 |
| Ashcroft Real Estate Group Ltd | Real estate | 2025 |
| Ashcroft Transmissions Limited | Wholesale & retail | 1999 |
| Ashe Construction Limited | Construction | 1989 |
| Ashe Developments Limited | Construction | 2021 |
| Ashe Group Holdings Limited | Construction | 1972 |
| Ashe Roofing Limited | Construction | 2016 |
| Ashewood Rustics Ltd | Real estate | 2023 |
| Ashfield Electrical Limited | Construction | 2026 |
| Ashleys (Hertfordshire) Limited | Extraterritorial | 1999 |
| Ashleys (Hitchin) Limited | Other services | 1999 |
| Ashleys Group Limited | Extraterritorial | 1999 |
| Ashmi Corp (UK) Limited | Wholesale & retail | 2023 |
| Ashwell Ventures Limited | Wholesale & retail | 2004 |
| Asia Fixing Testing Ltd | Professional & scientific | 2025 |
| ASK08 Holdings Ltd | Financial services | 2022 |
| Aspace Property Limited | Real estate | 2017 |
| Aspen Institute UK | Information & communication | 2017 |
| Aspendale Investments Ltd | Real estate | 2015 |
| Asphalt Laboratory Supplies Ltd | Other services | 2022 |
| Aspire Cambridge Travel Ltd | Administrative & support | 2021 |
| Aspire Networks Limited | Extraterritorial | 2007 |
| Aspire Voyage Limited | Administrative & support | 2019 |
| Assembly Technologies Limited | Information & communication | 2023 |
| Associated National Electrical Wholesalers Limited | Other services | 1993 |
| Association for Rational Emotive Behaviour Therapy | Other services | 2002 |
| Assuretrust Asset Management Limited | Real estate | 2010 |
| Aston Building & Maintenance Limited | Real estate | 2003 |
| Aston Garden Machinery & Repairs Limited | Manufacturing | 2024 |
| Astreo HR Limited | Professional & scientific | 2026 |
| Astute Healthcare Limited | Wholesale & retail | 2012 |
| Astute Training Limited | Administrative & support | 2005 |
| Astute Wholesale Limited | Wholesale & retail | 2022 |
| ATD Legal & Compliance Services Limited | Professional & scientific | 2014 |
| Atdeals Ltd | Wholesale & retail | 2023 |
| Atec Mechanical Services Ltd | Construction | 2018 |
| Atelier Octive Limited | Professional & scientific | 2019 |
| Atmis Enterprises Ltd | Wholesale & retail | 2015 |
| Atwell Limited | Manufacturing | 1989 |
| Aubrey Consultants Limited | Real estate | 2013 |
| Audit Span Ltd | Professional & scientific | 2025 |
| Audrey Grace Ltd | Extraterritorial | 2024 |
| Augeo Investment Management UK Ltd | Real estate | 2019 |
| Augustus Machine Works Limited | Information & communication | 2015 |
| Aujla Ventures Ltd | Real estate | 2025 |
| AUM Incorporated Limited | Manufacturing | 2021 |
| Aumotiv Ltd | Administrative & support | 2025 |
| Aura Skin Collective Ltd | Other services | 2025 |
| Auric Development Ltd | Construction | 2026 |
| Auric LAB Ltd | Manufacturing | 2026 |
| Auro Centre for Integral Health Ltd | Education | 2025 |
| Aurora Family Mediation Limited | Health & social care | 2012 |
| Aurum Estates Limited | Real estate | 2013 |
| Aurum Haven Maintenance Services Ltd | Construction | 2026 |
| Aurum Intelligence Ltd | Information & communication | 2026 |
| Authum Care Limited | Health & social care | 2020 |
| Authum Properties Limited | Real estate | 2025 |
| Autismcan Ltd | Professional & scientific | 2010 |
| Auto Secured Ltd | Professional & scientific | 2021 |
| Autoklass Ltd | Wholesale & retail | 2023 |
| Autopoint Hitchin Limited | Real estate | 2023 |
| Autotech Consultant Services Limited | Other services | 2000 |
| Autowelt Ltd | Wholesale & retail | 2024 |
| AV Contracting Limited | Construction | 2012 |
| AV Project Management Limited | Information & communication | 2014 |
| Avalandia Limited | Information & communication | 2024 |
| Avallon Enterprise Limited | Hospitality | 2024 |
| Avanterra Holdings Ltd | Financial services | 2025 |
| Avanterra Innovations Ltd | Professional & scientific | 2025 |
| Avanti Advisory Limited | Hospitality | 2020 |
| Avanti Grill Limited | Hospitality | 2021 |
| Avayu Limited | Information & communication | 2022 |
| Aventus Clinic Limited | Health & social care | 2021 |
| Aviary Creative Limited | Professional & scientific | 2012 |
| AW Bicester Limited | Other services | 2021 |
| Awake People Coffee Limited | Wholesale & retail | 2026 |