| Athenbourne Limited | Real estate | 1982 |
| Athenlay Properties Limited | Real estate | 1969 |
| Athlete Way Always (AWA) Ltd | Arts & recreation | 2024 |
| Athlos Sport UK Limited | Wholesale & retail | 2025 |
| Atil News Limited | Wholesale & retail | 2008 |
| Atincola Ltd | Manufacturing | 2026 |
| Atkins Care Ltd | Health & social care | 2025 |
| Atlanta Building Residents Company Limited | Households | 2013 |
| Atlantic Fine Foods Ltd | Wholesale & retail | 2026 |
| Atlantic Forwarding (UK) Limited | Administrative & support | 2008 |
| Atlantic Seven Music Library Limited | Other services | 1988 |
| Atlantic Seven Productions Limited | Arts & recreation | 1984 |
| Atlantic Star Battersea Limited | Hospitality | 2022 |
| Atlantic Star Hospitality Limited | Hospitality | 2022 |
| Atlantico (UK) Limited | Wholesale & retail | 1995 |
| Atlantis Heights Limited | Real estate | 2022 |
| Atlas Computers Ltd | Wholesale & retail | 2021 |
| Atlas Couriers Limited | Information & communication | 2004 |
| Atlas DC Solutions Ltd | Professional & scientific | 2021 |
| Atlas Driving School Limited | Education | 2007 |
| Atlas Investments (London) Limited | Real estate | 2017 |
| Atlas Logistics Limited | Professional & scientific | 2000 |
| Atlas Tech & IT Solutions Ltd | Information & communication | 2017 |
| Atlas Technology Limited | Information & communication | 2024 |
| Atlas TM Ltd | Construction | 2021 |
| Atlas Truck & Plant Limited | Wholesale & retail | 2012 |
| Atmali RAF Ltd | Extraterritorial | 2017 |
| Atomma Ltd | Wholesale & retail | 2018 |
| Atop Limited | Construction | 2017 |
| Atoz Courier Services Limited | Transport & logistics | 1996 |
| Atoz Mobile Tyres Ltd | Wholesale & retail | 2026 |
| Atrs Homes Ltd | Real estate | 2024 |
| ATS Seven Express Ltd | Wholesale & retail | 2025 |
| Attendo Healthcare Services Limited | Health & social care | 2023 |
| Atticus Geoscience Consulting Ltd | Professional & scientific | 2022 |
| Attock Limited | Professional & scientific | 2012 |
| Attock OIL Company Limited(The) | Mining & quarrying | 1913 |
| Attrills DRY Cleaners Limited | Other services | 2014 |
| ATY Capital Ventures Limited | Real estate | 2021 |
| ATZ Construction & Maintenance Ltd | Construction | 2021 |
| AU and Co Consulting Ltd | Professional & scientific | 2024 |
| AU and Co Holdings Ltd | Financial services | 2023 |
| AU Buy to LET Property Limited | Real estate | 2021 |
| Audio Inspired Running Ltd | Other services | 2005 |
| Audio Visual Events Limited | Administrative & support | 2001 |
| Audiovisualdave Limited | Administrative & support | 2016 |
| Audit Investments Ltd. | Administrative & support | 2020 |
| Augustova Ltd | Information & communication | 2026 |
| Augustus Harvey Limited | Wholesale & retail | 2014 |
| Aujla & Co Services Limited | Real estate | 2019 |
| Aujla Cars Limited | Wholesale & retail | 2023 |
| Aujla Empire & Properties Ltd | Real estate | 2024 |
| Aujla Empire Limited | Real estate | 2021 |
| Aujla Trading Company Limited | Wholesale & retail | 2019 |
| Auka Productions Limited | Arts & recreation | 2025 |
| Aultone Way (Sutton) Management Limited | Households | 2006 |
| AUM Property Sutton Ltd | Real estate | 2023 |
| Aumex Limited | Extraterritorial | 1980 |
| Auntie Ann's Day Nursery Ltd | Education | 2013 |
| AUR Vegetables Limited | Wholesale & retail | 2025 |
| Aura Aesthetics London Ltd | Other services | 2024 |
| Aura Air Conditioning & Heating Ltd | Manufacturing | 2008 |
| Aura Homes London Ltd | Real estate | 2022 |
| Aura Interior Solutions Limited | Manufacturing | 2026 |
| Aurasculpt Studio Limited | Arts & recreation | 2026 |
| Aurasolutionslondon Ltd | Other services | 2025 |
| Aurelia Art Studios Ltd | Arts & recreation | 2023 |
| Aurimas Limited | Construction | 2016 |
| Aurora Building & Constructions Limited | Real estate | 2022 |
| Aurora Consultancy Practice Limited | Information & communication | 2019 |
| Aurora Eyecare Ltd | Wholesale & retail | 2026 |
| Aurora Nail Beauty Limited | Other services | 2026 |
| Aurora Swansea Marina (Management) RTM Company Limited | Households | 2011 |
| Aurora Swansea Marina Limited | Households | 2010 |
| Aurora Team Ltd | Households | 2021 |
| Auréllienne Ltd | Wholesale & retail | 2025 |
| Austin and Co Accountants Limited | Professional & scientific | 2015 |
| Austin Court Management Company Limited | Households | 1999 |
| Austin Dunwoody Limited | Professional & scientific | 2026 |
| Austins of Peckham Ltd | Hospitality | 2022 |
| Austin’S of London HLD Limited | Hospitality | 2020 |
| Austral Glazing Ltd | Construction | 2024 |
| Australia United MAI TU Agriculture Co., Ltd | Administrative & support | 2024 |
| Authentic Blends by Chopchop Ltd | Wholesale & retail | 2025 |
| Authentics (Trading) Limited | Wholesale & retail | 1992 |
| Authorcraft Ltd | Information & communication | 2010 |
| Authoritize Ltd | Information & communication | 2018 |
| Autism Among US CIC | Wholesale & retail | 2024 |
| Auto Correction Ltd | Wholesale & retail | 2021 |
| Auto House Limited | Other services | 2017 |
| Auto Image London Limited | Manufacturing | 2016 |
| Auto Impartial Ltd | Information & communication | 2024 |
| Auto Italia Ltd | Extraterritorial | 2024 |
| Auto Service Express Ltd | Wholesale & retail | 2020 |
| Automagical Ltd | Information & communication | 2019 |
| Automotive Glass Doctor Ltd | Wholesale & retail | 2023 |
| Automotive Project Engineering Consultancy Ltd. | Professional & scientific | 1994 |
| Autopro Motors Limited | Wholesale & retail | 2024 |
| Autosolutions Automotive Electronics Ltd | Wholesale & retail | 2021 |
| Autotaps (UK) Limited | Manufacturing | 2013 |