| Antony Retail Ltd | Wholesale & retail | 2012 |
| ANU Marma Therapy Ltd | Health & social care | 2024 |
| Anukampa Bhikkhuni Project | Other services | 2016 |
| Anuna Limited | Professional & scientific | 2014 |
| Aotearoa Productions Limited | Administrative & support | 2007 |
| AP Design Studios Ltd | Professional & scientific | 2024 |
| AP Live Ltd | Administrative & support | 2021 |
| Apex Roofing & Scaffolding Limited | Construction | 1996 |
| Apocalypse Paintball Limited | Arts & recreation | 2003 |
| Apotek AV Limited | Professional & scientific | 2011 |
| Apple Tree Trade Ltd | Wholesale & retail | 2026 |
| Applehill Properties Ltd | Administrative & support | 2010 |
| Appliance Kings Ltd | Wholesale & retail | 2026 |
| Arap Trading Ltd | Hospitality | 2023 |
| Arbon & Turner Ltd | Professional & scientific | 2011 |
| Arbury Acupuncture Limited | Health & social care | 2024 |
| ARC (UK) Limited | Wholesale & retail | 2005 |
| Archella Consultants LLP | | 2012 |
| Archer Peers & Co Limited | Real estate | 2016 |
| Arcovia Limited | Real estate | 2019 |
| Arcus Cloud Consulting Ltd | Information & communication | 2023 |
| Ardent Construction Ltd | Construction | 2016 |
| Areia Media Limited | Professional & scientific | 1999 |
| Arena Festival Consultancy Limited | Professional & scientific | 2025 |
| Ariadne Search Limited | Administrative & support | 2018 |
| Aristo (Catering) Limited | Financial services | 1939 |
| Aristo Trading Company Limited | Administrative & support | 1986 |
| Arke Life & Legacy Ltd | Administrative & support | 2025 |
| Arkey Ltd | Financial services | 2024 |
| Arnold Guise Associates Limited | Professional & scientific | 1994 |
| Arnolds Development Company Limited | Real estate | 1999 |
| Aromachat Productions Ltd | Information & communication | 2014 |
| Artemis Consultants Limited | Information & communication | 2016 |
| Artemis Property Holdings Limited | Construction | 2023 |
| Artis Renewables Limited | Construction | 2021 |
| Asahi Glassplant Holdings Ltd | Financial services | 2019 |
| Asahi Glassplant UK Ltd | Manufacturing | 2019 |
| Asap Royston Taxis Ltd | Transport & logistics | 2024 |
| Ascension TV Ltd | Information & communication | 2018 |
| Asco Consulting Limited | Professional & scientific | 2022 |
| Ashlea Foster Ltd | Real estate | 2025 |
| Ashlea Harefield Ltd | Construction | 2026 |
| Ashlea Network Ltd | Construction | 2022 |
| Ashley Stewart Ltd. | Administrative & support | 1992 |
| Ashwood and Grace Ltd | Administrative & support | 2018 |
| Askar Research Ltd | Information & communication | 2025 |
| Asmble Ltd | Information & communication | 2013 |
| Aspenden Farming Ltd | Agriculture & fishing | 2018 |
| ASR Media Tech Ltd | Other services | 2018 |
| Astranest Ltd | Wholesale & retail | 2025 |
| Astutim Limited | Professional & scientific | 2009 |
| ASW Investment Limited | Professional & scientific | 2010 |
| ATL Advisory Services Ltd | Information & communication | 2018 |
| Atspace Limited | Construction | 2012 |
| Atterton Productions Limited | Information & communication | 2016 |
| Attingham Estates Ltd | Construction | 2024 |
| Attingham Properties Ltd | Construction | 2026 |
| Audhd Counselling Community Interest Company | Health & social care | 2025 |
| Autajon Labels Royston England Limited | Manufacturing | 1995 |
| Auto Fanatics Ltd | Wholesale & retail | 2022 |
| Autogate Services and Installation Ltd. | Manufacturing | 2000 |
| Avante Garde Ltd | Manufacturing | 2011 |
| Avanza IT Services Ltd | Other services | 2020 |
| Avcon Training and Consulting Ltd | Transport & logistics | 2025 |
| Avenue Property Management (Cambs) Ltd | Real estate | 2006 |
| Avril Healthcare Limited | Administrative & support | 2023 |
| Awards International Limited | Professional & scientific | 2008 |
| AWR Mortgages Ltd | Financial services | 2021 |
| Axcelerate Consulting Limited | Professional & scientific | 2025 |
| Axios Big Red Ltd | Construction | 2015 |
| B Barnard Ltd | Construction | 2018 |
| B C Consult Ltd | Information & communication | 2023 |
| B S P Labels Limited | Manufacturing | 2000 |
| B&D Assets Ltd | Real estate | 2022 |
| B&M Corp Limited | Administrative & support | 2016 |
| B&T Accountants Ltd | Professional & scientific | 2018 |
| B.A. Hydro Solutions Limited | Professional & scientific | 2012 |
| B.P.Herbs Ltd | Agriculture & fishing | 2025 |
| B.W.C. Contracts Limited | Construction | 2004 |
| Baer Gellert Ltd | Professional & scientific | 2003 |
| BAG END Consulting Limited | Professional & scientific | 2023 |
| BAG END Farm Ltd | Agriculture & fishing | 2022 |
| Bajaj Security Ltd | Administrative & support | 2025 |
| Bakewell Mews Residents Management Company Limited | Households | 2011 |
| Balco Designs Limited | Wholesale & retail | 2023 |
| Baltic Nomad Ltd | Manufacturing | 2022 |
| Bampton Stone Limited | Mining & quarrying | 2012 |
| Bananapad Limited | Wholesale & retail | 2025 |
| Banatan Veronica Ltd | Manufacturing | 2026 |
| Bando Baby Ltd | Wholesale & retail | 2021 |
| Bands and Brands Ltd | Information & communication | 2012 |
| Barathy Retail Ltd | Wholesale & retail | 2019 |
| Barbisol Limited | Construction | 1964 |
| Barcan Limited | Information & communication | 2010 |
| Bardachoice Limited | Households | 1977 |
| Bardwell Winter Limited | Construction | 2015 |
| Barefoot Property Partners Ltd | Real estate | 2022 |
| Barker's Turkeys Limited | Agriculture & fishing | 1985 |
| Barkway Court Management Company Limited | Households | 1987 |
| Barkway Property Management Ltd | Households | 2022 |