| Aricia Limited | Administrative & support | 2001 |
| Arics Limited | Extraterritorial | 2000 |
| Arics Properties Holdings LLP | | 2001 |
| Arics Properties Limited | Real estate | 2021 |
| Arise Youth Support Limited | Health & social care | 2022 |
| Arishfa Haque Company Limited | Wholesale & retail | 2024 |
| Arlescote Farm Ltd. | Real estate | 2019 |
| Armore Limited | Professional & scientific | 2013 |
| Arnott Mackenzie Ltd | Professional & scientific | 2023 |
| Arok Holdings Ltd | Real estate | 2026 |
| Aromont&Co. Ltd | Wholesale & retail | 2025 |
| Aronmoor Property Management Limited | Hospitality | 2000 |
| Art Contracts Limited | Construction | 2002 |
| Art Roofing Limited | Extraterritorial | 2006 |
| Arte-Panel Ltd | Extraterritorial | 2015 |
| Arthrofilm Ltd | Information & communication | 2016 |
| Artisan Woodcraft Limited | Construction | 1997 |
| Artisancraftprops Ltd | Wholesale & retail | 2025 |
| Artistswalls Ltd | Arts & recreation | 2022 |
| ASC Advocacy Ltd | Administrative & support | 2023 |
| Asenova Cleaning Limited | Administrative & support | 2012 |
| ASH and Rosewood Ltd | Arts & recreation | 2025 |
| ASH Prestige Cars Ltd | Transport & logistics | 2020 |
| Ashby Court (Residents) Management Limited | Real estate | 1989 |
| Ashcroft Therapy Centre Ltd | Real estate | 2013 |
| Ashlea Guest House Limited | Hospitality | 2017 |
| Ashley & Dumville Limited | Information & communication | 1928 |
| Asholly Luxe Ltd | Wholesale & retail | 2026 |
| Ashtop Enterprises Limited | Administrative & support | 2014 |
| ASK Alice VPA Limited | Administrative & support | 2023 |
| Askew Business Consulting Ltd | Professional & scientific | 2022 |
| ASL Demolition Ltd | Professional & scientific | 2020 |
| ASL Security Ltd | Administrative & support | 2026 |
| Asoko Box Limited | Wholesale & retail | 2018 |
| Asonz Limited | Administrative & support | 2016 |
| Aspect Arboriculture Limited | Agriculture & fishing | 2012 |
| Aspect Landscape Planning Holdings Ltd | Financial services | 2025 |
| Aspect Landscape Planning Limited | Professional & scientific | 2004 |
| Aspire Support (Northamptonshire) Ltd | Health & social care | 2025 |
| Aspireto Limited | Professional & scientific | 2014 |
| Asso Enterprise Ltd | Wholesale & retail | 2023 |
| Astech Consultants Limited | Information & communication | 1997 |
| Aster LEE Ltd | Construction | 2020 |
| Astley Building Services UK Ltd | Construction | 2012 |
| Aston Contracts and Maintenance Limited | Construction | 2017 |
| Aston Martin Racing Limited | Extraterritorial | 2007 |
| Aston Property Maintenance Ltd | Construction | 2022 |
| Astrop Capital | Financial services | 2017 |
| Astrop Farms Limited | Agriculture & fishing | 1995 |
| Astun Holdings Ltd | Financial services | 2021 |
| Astun Technology Limited | Information & communication | 2005 |
| Astyrian Legal & Consulting Limited | Professional & scientific | 2018 |
| Asura Design Limited | Professional & scientific | 2008 |
| ASY Ltd | Wholesale & retail | 2026 |
| AT Purpleorange Ltd | Administrative & support | 2007 |
| Athenian Consulting Limited | Professional & scientific | 2013 |
| Atico Import and Export Company Ltd | Wholesale & retail | 2024 |
| ATL Enterprise Ltd | Wholesale & retail | 2011 |
| Atlantic Flight Maintenance Limited | Extraterritorial | 2011 |
| Atlantis International Limited | Manufacturing | 1995 |
| Atlas Heating and Cooling Ltd | Construction | 2026 |
| ATM Food Innovations Limited | Professional & scientific | 2025 |
| Atomic Munki Corporation Ltd | Information & communication | 2017 |
| Atters Picture Company Ltd | Information & communication | 2011 |
| Atticist Productions Ltd | Arts & recreation | 2019 |
| Atticus Marcom Ltd | Professional & scientific | 2025 |
| Attley Cladding Limited | Construction | 1990 |
| Attley Roofing Limited | Construction | 2003 |
| Attleys Roofing Limited | Construction | 1986 |
| Aupa Wines Ltd | Wholesale & retail | 2026 |
| Aurelia International Ltd | Administrative & support | 2024 |
| Aurevia Capital Ltd | Financial services | 2025 |
| Aussie Boots Ltd | Wholesale & retail | 2018 |
| Austin-Segal Limited | Professional & scientific | 2019 |
| Authentic Things Limited | Other services | 2011 |
| Auto Action FX Ltd | Professional & scientific | 2013 |
| Auto Night Lights Limited | Manufacturing | 2025 |
| Autograph Automotive Limited | Wholesale & retail | 2020 |
| Automax (Banbury) Limited | Wholesale & retail | 2019 |
| Automotive Diagnostics International Ltd | Wholesale & retail | 2020 |
| Automotive Mobile Tyres Ltd | Wholesale & retail | 2025 |
| Automotive Performance Services (Brackley) Limited | Wholesale & retail | 2010 |
| Autonomous Group Ltd | Real estate | 2025 |
| Autotask Ltd | Information & communication | 2025 |
| Auxillius Excelsis Ltd | Professional & scientific | 2012 |
| Auxxano Ltd | Professional & scientific | 2011 |
| Auxxilia Limited | Administrative & support | 2017 |
| AV Cloud Tech Limited | Information & communication | 2019 |
| Avasa Financial Limited | Professional & scientific | 2014 |
| Aveco Electrical Systems Limited | Manufacturing | 2009 |
| Aveco Investments Limited | Financial services | 2016 |
| Avencourt Management Limited | Households | 1989 |
| Aventra Hospitality Limited | Administrative & support | 2024 |
| Avenue Investco Ltd | Real estate | 2022 |
| Avire UK Commercial Ltd | Real estate | 2020 |
| Avire UK Lettings Ltd | Real estate | 2025 |
| Avonbury Court Management Company Limited | Real estate | 2018 |
| Avonvale Veterinary Practice Limited | Professional & scientific | 2003 |
| AVR (Oxon) Limited | Health & social care | 2009 |
| Awardevents Limited | Hospitality | 2016 |