| ((Bounce)) BED Didcot Ltd | Arts & recreation | 2025 |
| 14TH Mile Ltd | Hospitality | 2026 |
| 20TWENTY Onward Ltd | Professional & scientific | 2019 |
| 23 Cumberland Street Management Company Limited | Households | 2001 |
| 27 Wessex Road (Didcot) Management Company Limited | Households | 2006 |
| 352 Abingdon Ltd | Real estate | 2025 |
| 354 Abingdon Ltd | Real estate | 2025 |
| 3DMAGINATION Ltd | Professional & scientific | 2015 |
| 3DWUK Ltd | Manufacturing | 2025 |
| 4E Products Limited | Manufacturing | 2013 |
| 5015 Limited | Financial services | 2025 |
| 5F Investments Ltd | Wholesale & retail | 2024 |
| 5IVE Management Limited | Administrative & support | 2004 |
| A a D Plumbing Ltd | Construction | 2014 |
| A Eltinay Consultancy Ltd | Health & social care | 2024 |
| A G Curtain Design Limited | Wholesale & retail | 2012 |
| A L Lacy & Sons Limited | Construction | 2005 |
| A L Rouse Ltd | Construction | 2018 |
| A Star Painting and Decorating Ltd | Construction | 2007 |
| A&G Landscapes Ltd | Administrative & support | 2014 |
| A.J.N Sibbs Holdings Ltd | Real estate | 2023 |
| A.Sip Trans Ltd | Transport & logistics | 2019 |
| AA Clinical Limited | Professional & scientific | 2020 |
| AA Elite Rugby Coaching Limited | Arts & recreation | 2015 |
| AA Signs Limited | Manufacturing | 2024 |
| Aacc LLP | | 2025 |
| Abbotts Farm (East Hagbourne) Ltd | Agriculture & fishing | 2017 |
| Abelonne Investments Limited | Real estate | 2024 |
| Abgerry Ltd | Professional & scientific | 2021 |
| ABI Driving Ltd | Education | 2025 |
| Abi-Support Ltd | Health & social care | 2020 |
| Absinthe Cleaners Ltd | Administrative & support | 2026 |
| Abstinium Limited | Information & communication | 2016 |
| Accentus Cardiac Ltd | Professional & scientific | 2014 |
| Accentus Dental Technologies Ltd | Health & social care | 2015 |
| Accentus Medical Limited | Professional & scientific | 2001 |
| Access to Care Services Ltd | Health & social care | 2024 |
| ACCOMOD8 Co-Living Limited | Real estate | 2023 |
| ACD Care Ltd | Health & social care | 2019 |
| Acorn Home Support Ltd | Health & social care | 2021 |
| Acorn Statistical Analysis Ltd | Administrative & support | 2023 |
| ACT Business Consultants Ltd | Professional & scientific | 2016 |
| Active Viii Limited | Health & social care | 2003 |
| AD Roofing Ltd | Construction | 2026 |
| Adagio Hearing Limited | Wholesale & retail | 2018 |
| Adam Miah Didcot Ltd | Hospitality | 2023 |
| Adlevo-Life Ltd | Wholesale & retail | 2019 |
| Adrn Investments Ltd | Real estate | 2025 |
| Advanced B-Solv Technology Limited | Professional & scientific | 2025 |
| Advanced Measurement Group Holdings Ltd | Real estate | 2025 |
| Advanced Property Systems Ltd | Real estate | 2025 |
| Advanced Research Clusters Developments Limited | Construction | 1998 |
| Advanced Research Clusters GP Limited | Financial services | 2001 |
| Advanced Research Clusters Holdco Limited | Financial services | 2017 |
| Advanced Research Clusters Management Limited | Real estate | 2013 |
| Advanced Research Clusters Portfolio Management Limited | Real estate | 2017 |
| Agamatrix Europe Limited | Health & social care | 2007 |
| Agan Property Limited | Real estate | 2018 |
| Agave Developments Limited | Real estate | 2024 |
| Agneash Limited | Information & communication | 2016 |
| Agriblue Consulting Ltd | Agriculture & fishing | 2024 |
| AGT Property Ltd | Real estate | 1995 |
| AH Electrical Ltd | Construction | 2017 |
| AIM2 Operational Consulting Ltd | Professional & scientific | 2025 |
| Aimark Ltd | Wholesale & retail | 2017 |
| Aino Audio Ltd | Professional & scientific | 2018 |
| Aiph UK Limited | Other services | 2019 |
| Airdrop Ltd | Information & communication | 2011 |
| Aishi Limited | Real estate | 2021 |
| Aixion IT Solutions Ltd | Information & communication | 2025 |
| AJ Holiday Lettings Ltd | Hospitality | 2020 |
| AJ Machinery Limited | Wholesale & retail | 1982 |
| AJC Property Investments Ltd | Real estate | 2011 |
| AJD Water Services Limited | Water & waste | 2019 |
| Akjel Limited | Financial services | 2024 |
| Akori Limited | Information & communication | 2000 |
| Akshaya Shivakari Limited | Real estate | 2022 |
| Aktive Solutions Limited | Other services | 2010 |
| AL Aioubi Limited | Professional & scientific | 2025 |
| Al-Hashmi Trading and Services Ltd | Wholesale & retail | 2016 |
| Alan Nicholas Salmon Ltd | Extraterritorial | 2025 |
| Alantera Unlimited | Professional & scientific | 2015 |
| Alba's Traditional Butchers Ltd | Wholesale & retail | 2017 |
| Alex Andrews Plumbing and Heating Ltd | Construction | 2018 |
| Alex Engineering Limited | Construction | 2010 |
| Alexander Delivery Ltd | Transport & logistics | 2025 |
| All-Round Marketing Ltd | Information & communication | 2023 |
| Allbrite Office & Window Cleaning Ltd | Administrative & support | 2011 |
| Allen (Hanford) Limited | Agriculture & fishing | 2000 |
| Allenfield Precision Engineering Limited | Manufacturing | 1965 |
| Allo Taxis Didcot Ltd | Transport & logistics | 2024 |
| Allroy Estates Ltd | Real estate | 2022 |
| Alltecnique Limited | Wholesale & retail | 2006 |
| Alma Barn LLP | | 2012 |
| Almayan Properties Ltd | Real estate | 2025 |
| Almimi Ltd | Transport & logistics | 2024 |
| ALP Pharmaservices Ltd | Professional & scientific | 2026 |
| Alpha Autoproducts Limited | Wholesale & retail | 2009 |
| Alpha Crestwood Limited | Real estate | 2024 |
| Alpha Packaging Limited | Wholesale & retail | 1993 |