| Associated Accountancy Services Limited | Professional & scientific | 2003 |
| Associated Computer Services Ltd | Information & communication | 2021 |
| Association for Physical Education | Education | 2005 |
| Astons Coaches Limited | Transport & logistics | 2000 |
| Astoria Elite Care Limited | Public administration | 2022 |
| Astound Studio Limited | Professional & scientific | 2022 |
| Astwood Estates Ltd | Real estate | 2020 |
| Astwood Road Management Company Limited | Households | 2023 |
| Ataraxia Group Ltd | Real estate | 2022 |
| ATD Business Ltd | Financial services | 2019 |
| ATD Property Ltd | Real estate | 2023 |
| Atelier by Charlotte Ltd | Other services | 2025 |
| Atelier Floors Limited | Wholesale & retail | 2011 |
| Ateq Consulting Limited | Professional & scientific | 2015 |
| Athena Financial Planning Limited | Financial services | 2007 |
| Atlanta Cleaners Ltd | Other services | 2025 |
| Atlanta Fast Food Ltd | Hospitality | 2025 |
| Atlanta Trade Ltd | Wholesale & retail | 2025 |
| Atlas Sports Software Limited | Arts & recreation | 2023 |
| ATM Asset Haven Ltd | Real estate | 2025 |
| Atmos Bookkeeping Ltd | Professional & scientific | 2019 |
| Atoll Capital Limited | Financial services | 2012 |
| Atomic ARC Ltd | Information & communication | 2025 |
| Atrium Conservatories Ltd | Manufacturing | 2012 |
| Attano Ltd | Information & communication | 2014 |
| Attavanti Limited | Wholesale & retail | 2012 |
| Attention to Detail Plumbing & Heating Limited | Construction | 2014 |
| Atwell Engineering Solutions Ltd | Professional & scientific | 2016 |
| Atwell International Limited | Manufacturing | 1996 |
| Audio Definition Limited | Manufacturing | 2006 |
| Auntie Em's Tea & Toy Emporium Ltd | Wholesale & retail | 2019 |
| Aura Delicious Food Ltd | Hospitality | 2024 |
| Aura Newns Limited | Professional & scientific | 2023 |
| Aura Rosa Limited | Health & social care | 2025 |
| Auraya Systems UK Limited | Professional & scientific | 2020 |
| Aurelian Services Ltd | Transport & logistics | 2021 |
| AUS Organically PTY Ltd | Manufacturing | 2024 |
| Auseful.Com Limited | Information & communication | 2009 |
| Austin Cleaning Ltd | Other services | 2025 |
| Austin Fast Food Ltd | Hospitality | 2025 |
| Austins Cleaning Services Ltd | Administrative & support | 2022 |
| Auto FIX Bristol Ltd | Wholesale & retail | 2025 |
| Auto GAS Technology Limited | Administrative & support | 1998 |
| Auto Glaze Solutions Limited | Wholesale & retail | 2019 |
| Auto K (Worcester) Limited | Wholesale & retail | 2007 |
| Autocool (South Wales) Limited | Wholesale & retail | 2006 |
| Autoflo Hand Wash Systems Ltd | Manufacturing | 2009 |
| Autograph Finance Ltd | Financial services | 2021 |
| Automated Abodes Ltd | Construction | 2020 |
| Automatica Systems Ltd | Professional & scientific | 2024 |
| Automation Software Engineering Limited | Professional & scientific | 2023 |
| Automotive Artisans Limited | Manufacturing | 2025 |
| AV Actuators Limited | Manufacturing | 2014 |
| AV Automation Limited | Professional & scientific | 2023 |
| AV Global Group Limited | Financial services | 2022 |
| AV Megaline Ltd | Construction | 2016 |
| AV Smart Tech Limited | Professional & scientific | 2023 |
| Avalon Housing Ltd | Real estate | 2023 |
| Avanti Business Support Ltd | Administrative & support | 2015 |
| Avenbury Care Farm C.I.C. | Health & social care | 2016 |
| Avenbury Ledbury Ltd | Real estate | 2025 |
| Avenbury Securities Ltd | Real estate | 2024 |
| Avenue Services (NW) Limited | Administrative & support | 2012 |
| Aver Resources Ltd | Other services | 2023 |
| Avern Cleaning Supplies (Internet) Limited | Wholesale & retail | 2017 |
| Avery Landscapes Limited | Construction | 2014 |
| AVG Automation Limited | Professional & scientific | 2023 |
| AVG Tech Limited | Professional & scientific | 2023 |
| AVG Technology Limited | Professional & scientific | 2023 |
| Aviacrown Limited | Health & social care | 1989 |
| Avon Resources Ltd | Other services | 2020 |
| Avoncroft Museum of Historic Buildings | Arts & recreation | 1964 |
| AVR Cleaning Ltd | Administrative & support | 2024 |
| AVR Consultancy Limited | Information & communication | 2024 |
| AVR Property Management Ltd | Real estate | 2024 |
| AVR Resources Ltd | Hospitality | 2023 |
| Avra Skin Limited | Health & social care | 2025 |
| Avtar (UK) Ltd | Health & social care | 2012 |
| AW Repair Group Limited | Wholesale & retail | 1999 |
| AWL Retail & Leisure Limited | Professional & scientific | 2024 |
| Awlborn Limited | Administrative & support | 2003 |
| AXE Junkies Ltd | Arts & recreation | 2020 |
| Axholme Cable Installations Limited | Construction | 2002 |
| Axionx Ltd | Professional & scientific | 2025 |
| Axiski Ltd | Arts & recreation | 2010 |
| AXM Asset Management London Limited | Administrative & support | 2021 |
| Axtell-Powell Developments Limited | Construction | 2006 |
| Aymestrey Court Management Limited | Households | 2004 |
| Azer Medical Limited | Health & social care | 2024 |
| Aziz Capital Ltd | Real estate | 2024 |
| Aziz Property Ltd | Real estate | 2022 |
| Azko Capital Ltd | Real estate | 2026 |
| Azmat Riaz Limited | Real estate | 2008 |
| AZU Chique Boutique Ltd | Wholesale & retail | 2026 |
| B & P Joinery Limited | Professional & scientific | 2001 |
| B G Sports Horses Limited | Agriculture & fishing | 2020 |
| B Hodgkiss Constructions Limited | Construction | 2003 |
| B M Agri. Engineering Ltd | Manufacturing | 2022 |
| B R Callow Limited | Construction | 2002 |
| B Smith Packaging (Manchester) Limited | Administrative & support | 1999 |