| Ambitech-It Limited | Information & communication | 2017 |
| Amethyst Sky Properties Ltd | Real estate | 2022 |
| AMO Automotive Ltd | Extraterritorial | 2022 |
| Amron Rail Services Ltd | Other services | 2020 |
| AMS Rentals Ltd | Extraterritorial | 2025 |
| Amstel Fund Management Limited | Financial services | 2016 |
| Amstel Securities UK Limited | Administrative & support | 2012 |
| AMW Legal Services Limited | Professional & scientific | 2022 |
| AMY Iddon Consulting Limited | Other services | 2019 |
| ANA & Will Ltd | Wholesale & retail | 2022 |
| Andover Tailors Limited | Manufacturing | 2025 |
| Andrew Murray & Co Ltd | Real estate | 2012 |
| Andy Crossey Music Limited | Information & communication | 2021 |
| Angel Aviation Consultancy Limited | Extraterritorial | 2019 |
| Angi Properties Ltd | Real estate | 2025 |
| Animal Antiks Education Limited | Education | 2022 |
| Anjali Property Rental 1 Ltd | Real estate | 2024 |
| Annacroff Ltd | Construction | 2023 |
| Anrui (Holdings) Europe Limited | Extraterritorial | 2019 |
| Anson & Mills Ltd | Other services | 2015 |
| Anson the Decorators Ltd | Construction | 2016 |
| ANT Carver Limited | Arts & recreation | 2013 |
| Antex Vintage Wholesale Limited | Wholesale & retail | 2021 |
| Anthistle Craven IRX Limited | Professional & scientific | 2018 |
| Anthistle Craven Ltd | Extraterritorial | 2003 |
| Anthony's Plumbing and Heating Limited | Wholesale & retail | 2013 |
| ANY Consultancy Ltd | Professional & scientific | 2017 |
| Aperio Group (Europe) Limited | Professional & scientific | 2010 |
| Apocan KBB Ltd | Hospitality | 2026 |
| Apollo 3 Management Company Limited | Real estate | 2006 |
| Apollo Business Parks Limited Liability Partnership | | 2001 |
| Apollo Construction and Development Limited | Construction | 2012 |
| Apollo Fifteen LLP | | 2024 |
| App Anthology Limited | Information & communication | 2026 |
| Applecado Ltd | Information & communication | 2010 |
| Appledore Holidays Limited | Real estate | 2009 |
| APT Education Recruitment Ltd | Education | 2025 |
| Apus Holdings Limited | Financial services | 2025 |
| Aqua Hydrous Capital Ltd | Hospitality | 2023 |
| Aqua Ozone Ltd | Other services | 2016 |
| Aquarius Plumbing Heating & Bathrooms Ltd | Construction | 1998 |
| AR Property Maintenance Services Ltd | Construction | 2025 |
| Arbiter Security Limited | Information & communication | 2024 |
| Arcadian Opera Limited | Arts & recreation | 2024 |
| Arcadian Opera Productions Limited | Arts & recreation | 2022 |
| Arch Fire IQ Ltd | Public administration | 2026 |
| ARD Property Services Company Limited | Real estate | 2014 |
| Areion Automotive Design Limited | Wholesale & retail | 2026 |
| Arena Pharmaceuticals Limited | Wholesale & retail | 2001 |
| Argento Investments Ltd | Other services | 2017 |
| Argo-Hytos Ltd | Manufacturing | 1991 |
| Aria Consulting Group Ltd | Professional & scientific | 2025 |
| Ariss Construction Limited | Construction | 2002 |
| Aristographyprints Ltd | Hospitality | 2014 |
| Ariya MK Limited | Real estate | 2019 |
| Armoury Detailing Ltd | Administrative & support | 2021 |
| Armstrong Wealth Limited | Professional & scientific | 2014 |
| Armstrong Wealth Services Ltd | Professional & scientific | 2021 |
| Arnico Holdings Ltd | Administrative & support | 2012 |
| Aroma 2025 Ltd | Hospitality | 2025 |
| Arrowhead Equity Ltd | Financial services | 2022 |
| Art of Nursing C.I.C. | Extraterritorial | 2012 |
| Art Profile Limited | Education | 2017 |
| Arthurs Radio Limited | Other services | 2000 |
| Arthurs Radio Salon Ltd | Other services | 2026 |
| ASC Group Limited | Information & communication | 2018 |
| ASG Acquisitions Limited | Real estate | 2021 |
| Ashley Griffiths Plumbing & Heating Limited | Construction | 2017 |
| ASK Install and Build Ltd | Construction | 2023 |
| Aspect Events Limited | Administrative & support | 2026 |
| Aspin Carpentry Ltd | Construction | 2022 |
| Aspirance Consulting Limited | Other services | 2013 |
| Aspire Extensions Ltd | Real estate | 2019 |
| Assa Property Ltd | Real estate | 2023 |
| Assured Medical Services Limited | Education | 2016 |
| Aster Interim Solutions Limited | Professional & scientific | 2003 |
| AT ME Solutions Limited | Information & communication | 2018 |
| Atic Banbury Limited | Extraterritorial | 2015 |
| Aticfour Limited | Extraterritorial | 2022 |
| Aticone Limited | Real estate | 2022 |
| Aticthree Ltd | Real estate | 2022 |
| Atictwo Ltd | Real estate | 2022 |
| ATK & Partners UK Limited | Wholesale & retail | 2011 |
| Atma Assets Ltd | Households | 2023 |
| ATN Farms Limited | Agriculture & fishing | 2016 |
| ATN Hawes Limited | Real estate | 2014 |
| Aura Static Beauty Ltd | Other services | 2026 |
| Auren Value Partners Ltd | Professional & scientific | 2025 |
| Aurora Tech Refurb & Resale Ltd | Other services | 2025 |
| Austerley Technology Group Ltd | Construction | 2020 |
| Austin Advisory Ltd | Professional & scientific | 2025 |
| Auto Effects Ltd | Wholesale & retail | 2009 |
| Auto Interiors Ltd | Manufacturing | 2017 |
| Autogatesuk Ltd | Construction | 2012 |
| Automec Equipment & Parts Limited | Wholesale & retail | 1977 |
| Automec Holdings Limited | Financial services | 2017 |
| Automotive Lean Consulting Ltd | Professional & scientific | 2011 |
| Autoswot Ltd | Education | 2019 |
| Avenue Farm Group Limited | Agriculture & fishing | 2025 |
| Avenue Farm Holdings Limited | Agriculture & fishing | 2025 |