| Arcplum Plumbing and Heating Ltd | Construction | 2024 |
| Arctoris Ltd | Professional & scientific | 2016 |
| Ardagh Estates Limited | Real estate | 2014 |
| Aris Investments Limited | Real estate | 2025 |
| Arkane Inc. Ltd | Manufacturing | 2021 |
| Arnco Scaffolding Group Ltd | Construction | 2019 |
| Arrow Scaffolding (Oxford) Ltd | Construction | 2013 |
| Art Solutions Ltd | Extraterritorial | 2014 |
| Art- BEA Limited | Health & social care | 2020 |
| Artan Yazilim Ltd | Wholesale & retail | 2025 |
| Artemas Joseph Holdings Ltd | Manufacturing | 2019 |
| Artificial Games Ltd | Information & communication | 2026 |
| Artisan Digital Holdings Limited | Financial services | 2013 |
| Artisan Leaves Ltd | Agriculture & fishing | 2023 |
| Artisan Litho Limited | Manufacturing | 2000 |
| Artistic Consulting Limited | Administrative & support | 2026 |
| Arttrees Studio Ltd | Manufacturing | 2024 |
| Arya ALI Ltd | Hospitality | 2025 |
| ASA Landscape Architects Ltd | Administrative & support | 2010 |
| Asas Automation Limited | Professional & scientific | 2009 |
| Ascot Hygiene Products Ltd | Wholesale & retail | 2015 |
| Ashby Precision Engineering Limited | Manufacturing | 1977 |
| Asher Productions Limited | Professional & scientific | 2018 |
| Ashley Box Limited | Professional & scientific | 2020 |
| Aside Creative UK Limited | Manufacturing | 2016 |
| Asnew Upholstery (Oxfordshire) Holdings Limited | Professional & scientific | 2012 |
| Asnew Upholstery Holdings Limited | Professional & scientific | 2023 |
| Asnew Upholstery Services Limited | Manufacturing | 2002 |
| Assana Limited | Real estate | 2024 |
| Aston Kitchens Limited | Manufacturing | 2006 |
| Aston Repair Depot Limited | Wholesale & retail | 2017 |
| Astra Bidco Limited | Financial services | 2021 |
| Astra Midco Limited | Financial services | 2021 |
| Astra Topco Limited | Financial services | 2021 |
| AT Motorsport Ltd | Professional & scientific | 2023 |
| ATA Classics Limited | Wholesale & retail | 2020 |
| ATB Properties Limited | Real estate | 2020 |
| Atlas Geoinformatics Ltd | Information & communication | 2024 |
| Atlas Renewables Ltd | Professional & scientific | 2020 |
| Atled Engineering Limited | Professional & scientific | 2023 |
| Atomizer Management Limited | Arts & recreation | 2012 |
| Atomizer Records Limited | Arts & recreation | 2017 |
| Atra Hasis Consulting Limited | Information & communication | 2025 |
| Attack Environmental Limited | Administrative & support | 2007 |
| Attitude Dance School Ltd | Arts & recreation | 2022 |
| Atwood Properties Limited | Real estate | 2020 |
| Auburn Zone Entertainment Ltd | Information & communication | 2020 |
| Audio Empire Ltd | Information & communication | 2023 |
| Audiox Consulting Ltd | Information & communication | 2022 |
| August & Spring Ltd | Professional & scientific | 2024 |
| Aurel Group Ltd | Wholesale & retail | 2026 |
| Aurelia House Ltd | Hospitality | 2026 |
| Aurora Bidco Limited | Financial services | 2020 |
| Aurora II Topco Limited | Financial services | 2020 |
| Aurora Midco 1 Limited | Financial services | 2020 |
| Aurora Midco 2 Limited | Financial services | 2020 |
| Austin-Mg-Sport Limited | Manufacturing | 2021 |
| Auto Joko Ltd | Wholesale & retail | 2013 |
| Auto-Check (Oxford) Limited | Wholesale & retail | 2014 |
| Autobahn Freightliner Ltd | Construction | 2025 |
| Autoexel Limited | Professional & scientific | 2004 |
| Autolog Ltd | Information & communication | 2026 |
| AV Boats Ltd | Manufacturing | 2014 |
| AV Clearance Limited | Administrative & support | 2025 |
| Available Workforce Ltd | Administrative & support | 2025 |
| Avatar Wellbeing Ltd | Other services | 2016 |
| Avaxmed Limited | Professional & scientific | 2017 |
| Avenna Ltd | Professional & scientific | 2017 |
| Avidel Limited | Professional & scientific | 2015 |
| AVJ Limited | Professional & scientific | 2021 |
| AVL Smile Holdings Ltd | Financial services | 2025 |
| AVL Smile Ltd | Health & social care | 2025 |
| AVL Smile Plus Ltd | Health & social care | 2019 |
| Awakening Group Limited | Construction | 2019 |
| Away From Home Clothing Ltd | Wholesale & retail | 2023 |
| AWF Prints Limited | Manufacturing | 2026 |
| Awip Collective Ltd | Arts & recreation | 2025 |
| Awip Creative Ltd | Arts & recreation | 2022 |
| AXO Clean Machines Trustees Limited | Administrative & support | 2019 |
| Axwr Limited | Hospitality | 2021 |
| AY Oxford Properties Limited | Real estate | 2019 |
| Ayana Solutions Ltd | Information & communication | 2020 |
| Aztex Solutions Ltd | Wholesale & retail | 2011 |
| Azure Solutions Limited | Professional & scientific | 2015 |
| Azzza Limited | Professional & scientific | 2008 |
| B & E Housing Limited | Real estate | 2002 |
| B & M Design & Advertising Limited | Professional & scientific | 2005 |
| B a Property Management Limited | Construction | 1992 |
| B COX Building Ltd | Construction | 2026 |
| B Flame Ltd | Construction | 2023 |
| B J & S Wallis Limited | Agriculture & fishing | 1988 |
| B&D Roper Limited | Administrative & support | 2008 |
| B2BBAY Ltd | Information & communication | 2025 |
| B2BOOST Ltd | Information & communication | 2026 |
| Babelquest Limited | Information & communication | 2010 |
| Backhen Ltd | Wholesale & retail | 2025 |
| Bader Aviation Art Ltd | Wholesale & retail | 2024 |
| Bader Fine Arts Ltd | Wholesale & retail | 2024 |
| Badger & Badger Ltd | Wholesale & retail | 2022 |
| Badger Business Solutions Ltd | Professional & scientific | 2025 |