| Alphalinen Limited | Other services | 2025 |
| ALT Hair Ltd | Other services | 2025 |
| Aluminium Profiles Supply UK Ltd | Wholesale & retail | 2024 |
| AM Developments (Oxfordshire) Limited | Real estate | 2016 |
| AM Drones Ltd | Other services | 2022 |
| AM Orthopaedic Limited | Health & social care | 2013 |
| AM PMU Academy Limited | Other services | 2025 |
| Amanda Stretton Limited | Information & communication | 2016 |
| Amara Attire Limited | Wholesale & retail | 2024 |
| Amarok Materials and Recycling Limited | Wholesale & retail | 2020 |
| Amarok Trading Limited | Wholesale & retail | 2020 |
| Ambgo Limited | Other services | 2022 |
| Ambion Consultants Limited | Professional & scientific | 1995 |
| Ambion Services Limited | Professional & scientific | 1999 |
| Ambroise Therapies Limited | Health & social care | 2025 |
| Ambrosden Leaf Limited | Wholesale & retail | 2008 |
| Amci Europe Limited | Professional & scientific | 2008 |
| Amerra Groundworks Limited | Construction | 2008 |
| AMG Asset Solutions Ltd | Administrative & support | 2015 |
| AMG Speed Trans Ltd | Transport & logistics | 2021 |
| Amgboys. Ltd | Arts & recreation | 2026 |
| Amici Bruerni | Education | 2010 |
| Amicus Asbestos Surveying Ltd | Other services | 2017 |
| Amicus Environmental Limited | Other services | 2010 |
| Amni Care Ltd | Information & communication | 2026 |
| Amonte Limited | Professional & scientific | 2010 |
| Amp-Air Services Ltd | Construction | 2021 |
| Ampernomics Ltd | Information & communication | 2026 |
| Amplo London Ltd | Professional & scientific | 2015 |
| AMS Insurance Services Limited | Financial services | 2000 |
| AMT Accounting Limited | Professional & scientific | 2011 |
| Analytichem Holding (UK) Limited | Financial services | 2023 |
| Analytichem UK Ltd | Manufacturing | 1974 |
| Anatomy Arts Piercing Limited | Arts & recreation | 2025 |
| Andcir Limited | Professional & scientific | 2011 |
| Andre R Ltd | Transport & logistics | 2017 |
| Andrew Cave Limited | Information & communication | 2005 |
| Andrew Hunter Limited | Administrative & support | 2002 |
| Andy Bevan Limited | Construction | 2015 |
| Andy Lloyd Ltd | Manufacturing | 2022 |
| Andy Winterbourne Carpentry & Construction Ltd | Construction | 2016 |
| Anergy Limited | Manufacturing | 2009 |
| Angels High Aviation Limited | Transport & logistics | 2022 |
| Anglo Pacific Consulting Limited | Wholesale & retail | 2012 |
| Angus Property Corporation Ltd | Real estate | 2024 |
| Anica DC Limited | Hospitality | 2019 |
| Aniface Limited | Information & communication | 2026 |
| Anish Care Services Ltd | Health & social care | 2006 |
| ANN and Maka Limited | Health & social care | 2015 |
| Annacat and Company Limited | Manufacturing | 1969 |
| Anne-Michelle Jewellery Ltd | Manufacturing | 2026 |
| Anomiebass Ltd | Health & social care | 2021 |
| Anserini Limited | Information & communication | 2016 |
| Anstie Properties Limited | Real estate | 2026 |
| ANT CAS Ltd | Information & communication | 2020 |
| Antem Services Limited | Information & communication | 2003 |
| Anthon&Gisele Ltd | Health & social care | 2023 |
| Antrobus Capital Partners Limited | Real estate | 2013 |
| Anushika Properties Limited | Real estate | 2014 |
| ANW Consultants Ltd | Information & communication | 2017 |
| AP & MP Limited | Other services | 2012 |
| AP Infra Limited | Professional & scientific | 2022 |
| APD Homes Ltd | Real estate | 2025 |
| Apex Commercial Management Limited | Professional & scientific | 2017 |
| Apex Equity Partners Ltd | Real estate | 2023 |
| Apex Fitness Studio Ltd | Arts & recreation | 2025 |
| Apex Loyalty Scaffolding Ltd | Construction | 2024 |
| APK Scaffold Supplies Ltd | Administrative & support | 2022 |
| Aplin Podiatry Limited | Health & social care | 2013 |
| Applied Landscape Design Limited | Professional & scientific | 2002 |
| Apricity Counselling Services Limited | Health & social care | 2023 |
| APT Support Ltd. | Professional & scientific | 2014 |
| Apteno Consulting Ltd | Professional & scientific | 2017 |
| Aqua People Healthcare Limited | Health & social care | 2025 |
| Aqua People Limited | Administrative & support | 2016 |
| Aqua Services (Oxford) Limited | Construction | 1999 |
| Aqualand Eco Systems Ltd | Wholesale & retail | 2025 |
| AR Hine Associates Limited | Administrative & support | 2008 |
| Aramz Properties Ltd | Real estate | 2024 |
| ARC Consulting Inc Limited | Construction | 2012 |
| ARC Properties Inc Limited | Construction | 2014 |
| Ardley Haulage Ltd | Transport & logistics | 2021 |
| Arena 14 Management Company Limited | Administrative & support | 2007 |
| Argent Capital Limited | Information & communication | 2025 |
| Argent DE Vincent Limited | Health & social care | 2019 |
| Argonaut Consulting Services (UK) Ltd | Information & communication | 2012 |
| Ario Advisory Limited | Financial services | 2016 |
| Arivea Ltd | Wholesale & retail | 2025 |
| ARK Investment Property Limited | Real estate | 2022 |
| Arkobuilder Ltd | Construction | 2023 |
| Aroma Foods Ltd | Hospitality | 2023 |
| Art Concierge London Ltd | Arts & recreation | 2025 |
| Art Engineering (OXF) Limited | Professional & scientific | 2022 |
| Art of 5 Limited | Other services | 2023 |
| Art VPS Limited | Information & communication | 2002 |
| Arthur Parkinson Ltd | Administrative & support | 2023 |
| Artisan Home Builds Ltd | Construction | 2025 |
| Artisan Practical Solutions Ltd | Manufacturing | 2020 |
| Artists & Objects Ltd | Wholesale & retail | 2019 |
| Artmis Limited | Extraterritorial | 2014 |