| Arjo Huntleigh International Limited | Professional & scientific | 1992 |
| Arjo Pension Trustee Limited | Financial services | 2016 |
| Arjo UK Limited | Manufacturing | 2017 |
| Arkkoz Ltd | Transport & logistics | 2015 |
| Armadyne Ltd | Information & communication | 2024 |
| Armak Property Investment Company Limited | Real estate | 2018 |
| Armer Sound and Light Ltd | Other services | 2016 |
| Armstrong Construction Limited | Construction | 2025 |
| Arniston Associates Limited | Real estate | 2001 |
| Aroca Ltd | Construction | 2021 |
| Aroma Cafe and Bite Limited | Hospitality | 2022 |
| Around the Clock Spedition Ltd | Transport & logistics | 2024 |
| Arran Mckeon Design Limited | Manufacturing | 2013 |
| Arshad Enterprises Ltd | Wholesale & retail | 2025 |
| Art on Computers Limited | Information & communication | 2017 |
| Artesa Ltd | Wholesale & retail | 2025 |
| Arthrocare Osteopathy and Sports Injury Clinic Limited | Health & social care | 2015 |
| Arthur & Emma Ltd | Wholesale & retail | 2019 |
| Arthur AI Limited | Information & communication | 2026 |
| Arthur AL Services Ltd | Construction | 2025 |
| Artisso Ltd | Manufacturing | 2018 |
| Arun Kumar Europe Limited | Construction | 2015 |
| Aryan Burford Ltd | Real estate | 2025 |
| Aryan Oxford Limited | Hospitality | 2018 |
| Aryzta Bakeries UK Ltd | Manufacturing | 1995 |
| ASA Business Limited | Professional & scientific | 2024 |
| Asaf LUX Limited | Other services | 2023 |
| ASB Global Services Ltd | Administrative & support | 2023 |
| Asbuilt Consulting Ltd | Professional & scientific | 2023 |
| Ascend Creative Limited | Information & communication | 2006 |
| Ascend Studio Limited | Information & communication | 2015 |
| Ascon Care Services Limited | Health & social care | 2019 |
| Ascot Automotive Ltd | Wholesale & retail | 2024 |
| Ascroft Heating Solutions Limited | Construction | 2021 |
| ASE Contracting Limited | Professional & scientific | 2014 |
| ASH Specialist Cars Ltd | Wholesale & retail | 2023 |
| Asha-Hope Consultancy Limited | Information & communication | 2012 |
| Ashengrove Fabrications Ltd | Manufacturing | 2022 |
| Ashland Fish Bar Ltd | Hospitality | 2026 |
| Ashley Vehicle Solutions Limited | Wholesale & retail | 2019 |
| Ashridge Partners Limited | Professional & scientific | 2014 |
| Ashton's Secretarial Limited | Professional & scientific | 2005 |
| Ashworth Design & Build Herts Limited | Construction | 2011 |
| Asian Snack Box Ltd | Hospitality | 2025 |
| ASK Here First Ltd | Administrative & support | 2023 |
| Askia Electrical Contractors Ltd | Administrative & support | 2017 |
| Asmark Services Limited | Professional & scientific | 2009 |
| Asociates Limited | Information & communication | 2025 |
| ASP Courier Ltd | Transport & logistics | 2021 |
| Aspect Carpet Holdings Limited | Financial services | 2016 |
| Aspect Carpet Installations Limited | Construction | 2000 |
| Aspen Accountancy Ltd | Professional & scientific | 2011 |
| Aspire to Inspire Community Interest Company | Education | 2018 |
| Aspirity Solutions Limited | Administrative & support | 2011 |
| Assk Ltd | Health & social care | 2018 |
| Associated Response Limited | Construction | 2026 |
| Associated Water Management Consultants Ltd. | Professional & scientific | 1997 |
| AST Dunstable Ltd | Construction | 2011 |
| Astwood Total Build Ltd | Construction | 2016 |
| ASZ Real Estate Ltd | Real estate | 2025 |
| ATB Electrical Services (Beds) Limited | Construction | 2016 |
| Atcar Service&Repair Ltd | Wholesale & retail | 2023 |
| ATD Plumbing, Heating and GAS Limited | Construction | 2022 |
| Atelier 56 Limited | Professional & scientific | 2018 |
| Athena Resourcing Services Limited | Wholesale & retail | 2025 |
| Athenians Limited | Real estate | 2000 |
| Atherton Limited | Real estate | 1987 |
| Atlantis Promotions Limited | Extraterritorial | 1997 |
| Atobabie Limited | Real estate | 2018 |
| Atom B.C. Ltd | Construction | 2014 |
| Auntytitis Kitchen Ltd | Hospitality | 2025 |
| Aura Estate Ltd | Real estate | 2019 |
| Auric Projects Limited | Construction | 2026 |
| Auron Builders Ltd | Construction | 2021 |
| Auto Body Ltd | Wholesale & retail | 2024 |
| Auto Electrical Services (Leighton Buzzard) Limited | Extraterritorial | 1992 |
| Auto Mall Ltd | Wholesale & retail | 2020 |
| Auto Prep Centre Limited | Wholesale & retail | 2025 |
| Auto Property Ltd | Construction | 2025 |
| Auto Repair Cars UK Ltd | Wholesale & retail | 2025 |
| Auto Zone Peterborough Ltd | Wholesale & retail | 2020 |
| Autobase London Ltd | Wholesale & retail | 2022 |
| Autobodykraft (LB) Ltd | Wholesale & retail | 2025 |
| Autocare MK12 Ltd | Wholesale & retail | 2024 |
| Autoland Engineering Limited | Wholesale & retail | 1999 |
| Autolusso Parts Limited | Wholesale & retail | 2010 |
| Automotive Specialist Associates Ltd | Professional & scientific | 2010 |
| AV Ecopacks Ltd | Wholesale & retail | 2025 |
| AV Refrigeration Ltd | Manufacturing | 2023 |
| Avant Events UK Ltd | Administrative & support | 2022 |
| Avea Services Limited | Professional & scientific | 2016 |
| Aventador Holdings Ltd | Manufacturing | 2022 |
| Avenue 21 Real Estate MH Limited | Real estate | 2023 |
| Avenue Road Management Company Limited(The) | Households | 1980 |
| Avhd Ltd | Construction | 2023 |
| Avian Facilities Management Ltd | Administrative & support | 2026 |
| Aviella Healthcare Ltd | Health & social care | 2025 |
| AVK Healthcare Ltd | Health & social care | 2022 |
| AW CNC Ltd | Manufacturing | 2026 |
| AW1 Homes Ltd | Real estate | 2025 |