| Amplify Creative Solutions Ltd | Professional & scientific | 2025 |
| Amptec Electrical Ltd | Other services | 2016 |
| AMR Electrical Contractors Limited | Construction | 2012 |
| Amsel & Wilkins LLP | | 2012 |
| Amzn'G Bites Ltd | Transport & logistics | 2025 |
| AN Lightside Holdings Ltd | Financial services | 2022 |
| AN Lightside Properties Ltd | Real estate | 2022 |
| ANA System Solutions Ltd | Transport & logistics | 2023 |
| Anam Cara Aviation Limited | Extraterritorial | 2010 |
| Anatawa Ltd | Information & communication | 2026 |
| Anatidae Capital Limited | Professional & scientific | 2017 |
| Ancitel E&A Limited | Professional & scientific | 2014 |
| Anderson Furniture Supplies Limited | Wholesale & retail | 2025 |
| Andrea Lamport Pro Skincare Ltd | Other services | 2017 |
| Andretti Formula E Limited | Professional & scientific | 2014 |
| Andretti United Extreme E Limited | Professional & scientific | 2020 |
| Andrew Baxter Civil & Structural Engineering Consultant Limited | Professional & scientific | 1993 |
| Andrew Buchanan Consultancy Ltd. | Professional & scientific | 1990 |
| Andrew Pinfold Limited | Construction | 2017 |
| Andronache Ltd | Construction | 2019 |
| Andtad Ltd | Financial services | 2025 |
| Andvest Ltd | Other services | 2010 |
| Andy Bewick Limited | Professional & scientific | 2017 |
| Andy Darby Electrical Limited | Construction | 2011 |
| Andy Milne Inventory Services Ltd | Administrative & support | 2010 |
| Andy Perry Ltd | Information & communication | 2020 |
| Andy Rush Media Ltd | Professional & scientific | 2026 |
| Andzelina Hurkacz Lettings Limited | Real estate | 2014 |
| Angela HR Ltd | Administrative & support | 2024 |
| Angleview Limited | Financial services | 2020 |
| Animals at Home (West Oxfordshire) Limited | Professional & scientific | 2018 |
| Animation Station Ltd | Arts & recreation | 2010 |
| ANN Holistic Care Ltd | Extraterritorial | 2016 |
| Anna Salon Ltd | Other services | 2015 |
| Anne Richardson Consulting Limited | Public administration | 2009 |
| Anneler GEE Limited | Information & communication | 2001 |
| Anode+- Ltd | Professional & scientific | 2020 |
| Anpr Consulting Ltd | Professional & scientific | 2013 |
| Anstruo IT Ltd | Information & communication | 2025 |
| Answerbuy Limited | Extraterritorial | 1987 |
| Antelope Hill Ltd | Real estate | 2020 |
| Anthony Shrimpton Design Ltd | Professional & scientific | 2013 |
| Anthrologica Ltd | Professional & scientific | 2012 |
| Anthrologica Plus Ltd | Professional & scientific | 2019 |
| Antique and Jewellery Roadshow Limited | Wholesale & retail | 2011 |
| Antrobus & Company LLP | | 2007 |
| Anvil Tool Company Limited | Wholesale & retail | 1991 |
| Anything Goes Services Ltd | Water & waste | 2024 |
| APC Cleaning & Maintenance Services Limited | Administrative & support | 1995 |
| APC Facilities Services Limited | Administrative & support | 2017 |
| APE Vision Limited | Arts & recreation | 2006 |
| Apel Consultancy Ltd | Professional & scientific | 2025 |
| Apeldoorn Studios Limited | Households | 1983 |
| Apex Designs Games LLP | | 2023 |
| Apex Powerwash Ltd | Administrative & support | 2024 |
| Apex Roofing Group Ltd | Construction | 2024 |
| APG TM Limited | Administrative & support | 2025 |
| APH Precision Fabrication Ltd | Manufacturing | 2015 |
| Aplc Support LLP | | 2015 |
| Apollo Nutrition Ltd | Health & social care | 2024 |
| Apollo Professional Services Ltd | Professional & scientific | 2013 |
| Apoloe Ltd | Health & social care | 2024 |
| Applegarth Nurseries Limited | Administrative & support | 2003 |
| Appostar Ltd | Information & communication | 2026 |
| Approved Packaging Services Limited | Wholesale & retail | 1986 |
| Aprobrium Distribution Limited | Wholesale & retail | 2020 |
| Aprobrium Limited | Information & communication | 1999 |
| APS Brackley Limited | Financial services | 2023 |
| APS Merlin Bodycraft (Brackley) Limited | Wholesale & retail | 2019 |
| APS Specialist Vehicles Limited | Wholesale & retail | 2018 |
| APT Event Services Ltd | Administrative & support | 2025 |
| Apti Taekwondo Limited | Arts & recreation | 2009 |
| Aqua Blast Pressure Washing Ltd | Administrative & support | 2022 |
| Aqua Clean Banbury Ltd | Administrative & support | 2021 |
| Aquadrop Property Solution Ltd | Real estate | 2026 |
| Aquila Learning Ltd | Information & communication | 2018 |
| AR Bespoke Travel Ltd | Other services | 2026 |
| AR Vehicle Recovery & Tyres Ltd | Transport & logistics | 2023 |
| Arab Research and Information Company Ltd | Information & communication | 1999 |
| Arabian Perfume Centre Ltd | Wholesale & retail | 2023 |
| Arbonica Ltd | Information & communication | 2026 |
| ARC Park Limited | Construction | 2025 |
| ARC Studios Limited | Arts & recreation | 2025 |
| Arcadian FOX Limited | Information & communication | 2019 |
| Archrise Roofing and Homes Ltd | Construction | 2025 |
| Arctic Trucks UK Limited | Wholesale & retail | 2008 |
| Arden International Limited | Arts & recreation | 1999 |
| Arden International Motorsport Limited | Arts & recreation | 1997 |
| Arden Motorsport Limited | Arts & recreation | 1996 |
| Arden Racing Limited | Extraterritorial | 2020 |
| Arden Self Storage Limited | Other services | 2006 |
| Arden Sports Management Limited | Professional & scientific | 2010 |
| Ardour Limited | Real estate | 2002 |
| Ardtrea Services Ltd | Professional & scientific | 2023 |
| Ardynt Consulting Limited | Professional & scientific | 2017 |
| Arena Corp. Limited | Hospitality | 2013 |
| Argenta Holdings International Limited | Administrative & support | 2022 |
| Argenta Projects Limited | Administrative & support | 2003 |
| Argenta Projects UK Limited | Administrative & support | 2021 |
| Aria-Roze Properties Ltd | Real estate | 2020 |