| AC Warehouse Trading Limited | Wholesale & retail | 2012 |
| ACADEMY55 Limited | Arts & recreation | 2025 |
| Accolo Limited | Administrative & support | 2023 |
| Ace Property Holdings Limited | Real estate | 2025 |
| Achieve Intelligence Ltd | Professional & scientific | 2018 |
| Acicularis Ltd | Professional & scientific | 2026 |
| Acorn Monitoring Ltd. | Information & communication | 2001 |
| Acorn Property Services and Maintenance Ltd | Construction | 2018 |
| Acorn to Oak Psychology Ltd | Education | 2026 |
| ACP Quality Produce Limited | Wholesale & retail | 2020 |
| Active Dynamics Technology Limited | Information & communication | 2015 |
| Active Vision Ltd | Transport & logistics | 2022 |
| ACW Accountancy Ltd | Professional & scientific | 2019 |
| Adam REX Finance Limited | Professional & scientific | 2024 |
| Adams Electrical Services (Oxford) Ltd | Construction | 2024 |
| Addiction Prescribing Service Limited | Health & social care | 2015 |
| Adenbourne Limited | Agriculture & fishing | 1998 |
| Adez Limited | Real estate | 2023 |
| Adhd Coaching With Anna Ltd | Education | 2025 |
| Aditech Limited | Other services | 1995 |
| Admlg Ltd | Hospitality | 2024 |
| Adonis Estates Limited | Real estate | 2015 |
| Adonis Holdings Limited | Financial services | 2015 |
| Adoptsmt UK Ltd. | Administrative & support | 2008 |
| Advance Choice Services Ltd | Health & social care | 2022 |
| Advanced Coaching & Education Ltd | Education | 2017 |
| Advanced Integrated Solutions (UK) Limited | Information & communication | 2013 |
| Advanced Repointing (UK) Limited | Construction | 2003 |
| Advisec Ltd | Information & communication | 2010 |
| AE Racing Ltd | Wholesale & retail | 2019 |
| Aegis Industrial Software (Europe) Limited | Information & communication | 2004 |
| Aesthetic 001 Ltd | Financial services | 2023 |
| AF HC Limited | Financial services | 2025 |
| Afromixx Entertainment Ltd | Information & communication | 2025 |
| AG Catering Food Ltd | Hospitality | 2025 |
| AG Livewell Ltd | Professional & scientific | 2026 |
| Agape Careline Ltd | Health & social care | 2018 |
| Agape Self Sufficiency | Administrative & support | 2018 |
| Agaram Designs Ltd | Manufacturing | 2026 |
| Aggia IT Services Ltd | Information & communication | 2024 |
| Agng Pumps & Injectors Service Ltd | Administrative & support | 2017 |
| Agoge Consulting Limited | Professional & scientific | 2016 |
| AGR Painting and Decorating Ltd | Construction | 2024 |
| Agten Property Ltd | Real estate | 2023 |
| Ahdb Limited | Health & social care | 2014 |
| AI Business Planning UK Limited | Information & communication | 2025 |
| Aikara Solutions Ltd | Information & communication | 2025 |
| Aileen Allkins Consultancy Limited | Professional & scientific | 2019 |
| AIM Car Park Limited | Administrative & support | 2015 |
| AIM Higher Training and Development Ltd | Administrative & support | 2016 |
| AIM Properties LLP | | 2011 |
| Aira Limited | Professional & scientific | 2018 |
| Airline Rotables (UK Holdings) Limited | Financial services | 1991 |
| Airtronic Solutions Ltd | Professional & scientific | 2014 |
| AJ and MJ Creations Limited | Manufacturing | 2021 |
| Ajlr Property Leasing Ltd | Real estate | 2022 |
| Ajlr Property Ltd | Real estate | 2022 |
| AJM Vehicle Movements Ltd | Wholesale & retail | 2025 |
| AJV Consult Limited | Professional & scientific | 2024 |
| AK Upvc Solutions Ltd | Construction | 2019 |
| Aker Systems Limited | Information & communication | 2016 |
| Aker Technology Services Limited | Information & communication | 2022 |
| Akifah Ltd | Wholesale & retail | 2021 |
| Akil Gulamali Limited | Health & social care | 2014 |
| Akka Services Ltd | Professional & scientific | 2022 |
| Akoya Biosciences UK Ltd. | Professional & scientific | 2018 |
| Aktana Limited | Administrative & support | 2016 |
| Akutaw Estates Limited | Real estate | 2024 |
| Aladukeh London Ltd | Arts & recreation | 2024 |
| Alan Imports Ltd | Wholesale & retail | 2020 |
| Albatrosstech Ltd | Manufacturing | 2020 |
| Albion and Phoenix Ltd | Wholesale & retail | 2026 |
| Alces Investments Limited | Real estate | 2014 |
| Alces Limited | Professional & scientific | 2014 |
| Alces Software Limited | Information & communication | 2008 |
| Alchester Construction Limited | Construction | 2016 |
| Alchester Holdings Ltd | Real estate | 2020 |
| Alchester Tiles Limited | Wholesale & retail | 2010 |
| Alchester Wealth Management Ltd | Real estate | 2023 |
| Alder House Limited | Real estate | 2022 |
| Aldred Casey Medical Ltd | Health & social care | 2014 |
| Alegros Tech Ltd | Information & communication | 2026 |
| Alex Enache Property Ltd | Real estate | 2024 |
| Alexander Associates Consultancy Limited | Administrative & support | 2014 |
| Alexandru Motors Ltd | Manufacturing | 2019 |
| Alftakins Ltd | Wholesale & retail | 2025 |
| Algar Seco Limited | Professional & scientific | 2018 |
| Alice in Wonderland Tattoo Studio Ltd | Arts & recreation | 2020 |
| Alin Diti Ltd | Transport & logistics | 2020 |
| Alisca Ltd | Other services | 2023 |
| ALL Yours Tattoo Co LLP | | 2022 |
| Allen and Kavanagh Automotive Services Ltd | Wholesale & retail | 2026 |
| Alliance Star Oxford Ltd | Administrative & support | 2021 |
| Allover Services Limited | Transport & logistics | 2023 |
| Allright Tyres Limited | Wholesale & retail | 2025 |
| Allscapes Gardens Limited | Construction | 2008 |
| Alma Properties (Bournemouth) LLP | | 2018 |
| Alozzu in Domu Ltd | Hospitality | 2018 |
| Alpas Property Ltd | Real estate | 2026 |
| Alphahaus Ltd | Other services | 2026 |