| Alpha Tutoring Oxfordshire Ltd | Education | 2021 |
| Alternative Energy Solutions (Service & Installation) Ltd | Energy | 2011 |
| AM Surface Technologies Limited | Professional & scientific | 2013 |
| AM Window Cleaning Limited | Administrative & support | 2013 |
| Amartya Group Limited | Information & communication | 2019 |
| Ambassadors of Christ Evangelistic Ministries | Other services | 2015 |
| Amber Therapeutics Holdings Limited | Professional & scientific | 2020 |
| Amber Therapeutics Limited | Professional & scientific | 1993 |
| Amcon Holdings Ltd | Real estate | 2025 |
| Amelia Space Technologies Ltd | Professional & scientific | 2023 |
| Amko Investments Ltd | Extraterritorial | 2014 |
| AML Bonders Ltd | Financial services | 2021 |
| Ampersand Design Limited | Administrative & support | 1994 |
| Ampregen Ltd | Wholesale & retail | 2013 |
| AMY16 Ltd | Transport & logistics | 2023 |
| Analogue Cameras Ltd | Professional & scientific | 2023 |
| Anashe Ltd | Other services | 2013 |
| Andrew Duxbury Limited | Professional & scientific | 2018 |
| Andrew M Sheard Consulting Ltd | Professional & scientific | 2025 |
| Andri Transport Ltd | Transport & logistics | 2015 |
| Andzelika Rojek Limited | Real estate | 2019 |
| Animal Magic Pony Parties Limited | Arts & recreation | 2006 |
| ANJ Afters Ltd | Manufacturing | 2025 |
| Anju Solutions Ltd | Information & communication | 2011 |
| Ankor Consulting Ltd | Professional & scientific | 2026 |
| Anmara Ltd | Real estate | 2022 |
| Anstis Consultancy Limited | Professional & scientific | 2007 |
| Apaara Tech Ltd | Information & communication | 2025 |
| Apex Business Growth Ltd | Administrative & support | 2025 |
| Apex Carpentry Ltd | Manufacturing | 2021 |
| Apex Datalogic Ltd | Information & communication | 2024 |
| Appally Limited | Information & communication | 2024 |
| Appandal Limited | Information & communication | 2015 |
| Applethorpe Developments Limited | Construction | 2016 |
| Applethorpe Properties Limited | Construction | 2020 |
| Applied Microengineering Limited | Manufacturing | 1992 |
| Aqua MAN Ltd | Administrative & support | 2019 |
| Aquaterra Limited | Construction | 1998 |
| Arbocare Tree Surgery and Landscaping Limited | Administrative & support | 2009 |
| ARC 1 Limited Partnership | | 2003 |
| ARC Development Management (UK) Limited | Construction | 2017 |
| ARC LP (UK) Limited | Financial services | 1993 |
| Arcgp 1 Limited | Real estate | 2003 |
| Arcgp 11 Limited | Real estate | 2012 |
| Arcgp 12 Limited | Real estate | 2012 |
| Arcgp 2 Limited | Real estate | 2003 |
| Archester Services Ltd | Construction | 2019 |
| Archimedes Circle Limited | Professional & scientific | 2025 |
| Arcik Trans Ltd | Manufacturing | 2023 |
| ARI Solutions Limited | Other services | 2023 |
| Ariat Europe Limited | Wholesale & retail | 1987 |
| Arjun Thiru Ltd | Real estate | 2020 |
| Arojek Limited | Real estate | 2024 |
| Art Sunshine Ltd | Wholesale & retail | 2024 |
| Art&J Ltd | Construction | 2026 |
| Artelna Limited | Financial services | 2010 |
| Artemis Investments Ltd | Real estate | 2025 |
| Artwin Electrics Ltd | Construction | 2024 |
| AS IF a Phoenix Ltd | Other services | 2025 |
| Asare Quality Care Limited | Health & social care | 2020 |
| ASH Farming LLP | | 2018 |
| Ashborough Investments Ltd | Real estate | 2021 |
| Ashbrook Limited | Construction | 1982 |
| Ashcroft Winrow Partnership Limited | Professional & scientific | 2015 |
| Ashdown Track Limited | Arts & recreation | 2005 |
| Ashram Consulting Ltd | Health & social care | 2025 |
| Ashurst Mortgage Solutions Limited | Financial services | 2014 |
| Asian Awards Limited | Administrative & support | 2010 |
| Asklepios Ltd | Health & social care | 2014 |
| Aspirants Consulting Services Limited | Information & communication | 2017 |
| Aspire Formwork Ltd | Construction | 2023 |
| Aspire Railways Ltd | Wholesale & retail | 2021 |
| Aspire Stays Ltd | Real estate | 2020 |
| Assemblon Limited | Professional & scientific | 2025 |
| Aston Beaufort Limited | Professional & scientific | 2019 |
| Aston Building (Conservation) Ltd | Construction | 2025 |
| Astons Online CIC | Information & communication | 2024 |
| Astroscale Ltd | Professional & scientific | 2017 |
| Astrosharp Limited | Information & communication | 2017 |
| ATA Logistics Ltd | Transport & logistics | 2017 |
| ATA Sameday Ltd | Transport & logistics | 2021 |
| Atomic Hair Limited | Other services | 2010 |
| Atrendz Supply Ltd. | Wholesale & retail | 2017 |
| Autism at Kingwood | Health & social care | 1994 |
| Auto Products Since 1973 Ltd | Manufacturing | 2025 |
| Autopic Technology Limited | Information & communication | 2026 |
| AVB Strategy Limited | Professional & scientific | 2022 |
| Avid Online Marketing Ltd | Extraterritorial | 2019 |
| Avidor Healthcare Ltd | Health & social care | 2022 |
| Awards of Distinction Limited | Wholesale & retail | 2013 |
| AWW Oxford Ltd | Transport & logistics | 2021 |
| Axion Test Engineering Limited | Professional & scientific | 2025 |
| Axsar Ltd | Information & communication | 2015 |
| Axtell Landscaping Ltd | Administrative & support | 2025 |
| Axxe Capital Ltd | Real estate | 2023 |
| Azco Direct Logistics Ltd | Transport & logistics | 2021 |
| B Global Controls Limited | Professional & scientific | 2006 |
| B Shaw Property Services Ltd | Real estate | 2022 |
| B&M Property Solutions Ltd | Real estate | 2013 |
| B. & N. Regal (Abingdon) Limited | Arts & recreation | 1977 |