| ALS Civil Engineers Holdings Limited | Construction | 2003 |
| Altaykay Ltd | Other services | 2025 |
| Aluminium Glazing Direct Ltd | Construction | 2021 |
| Alveo Architectura Ltd | Professional & scientific | 2020 |
| AM Academy Limited | Hospitality | 2012 |
| Ambition Sport Limited | Wholesale & retail | 2012 |
| Ameena Kara Callender Ltd | Information & communication | 2013 |
| AMH Investment Group Limited | Real estate | 2025 |
| Amiagab Limited | Health & social care | 2016 |
| Ammoudia Ltd | Real estate | 2021 |
| Amore Services Ltd | Administrative & support | 2021 |
| Amplify Operating Partners Ltd | Professional & scientific | 2025 |
| Anatomicals London (England, the World, the Universe-Known and Unknown) Ltd | Wholesale & retail | 2006 |
| AND NOW Partners Ltd | Professional & scientific | 2026 |
| Anderson Tyres Limited | Administrative & support | 2008 |
| Andre Hessler Limited | Professional & scientific | 2017 |
| Andrews of Kent Removals & Storage Limited | Transport & logistics | 2022 |
| Angelov UK Logistics Ltd | Transport & logistics | 2011 |
| Anglo Tech Services Ltd | Information & communication | 2019 |
| Anglo Windows Ltd | Construction | 2019 |
| Anna Woods Coaching Limited | Professional & scientific | 2020 |
| Annett Auto's Limited | Wholesale & retail | 2016 |
| Anthill Global Limited | Health & social care | 2012 |
| Anthony Jenkins Fuel OIL Limited | Wholesale & retail | 1971 |
| Anviet Limited | Hospitality | 2008 |
| Apex Kent Ltd | Construction | 2022 |
| Apex Quality Engineering Ltd | Manufacturing | 2015 |
| Apex South East Limited | Construction | 2025 |
| APG Contractors Ltd | Construction | 2022 |
| APG Properties Limited | Real estate | 2021 |
| APM Construction (South) Limited | Construction | 2016 |
| Apple Green Laundry Ltd | Administrative & support | 2023 |
| Approved Roofing & Home Improvements Ltd | Construction | 2021 |
| APS Property Services Ltd | Real estate | 2025 |
| Apsley & Wellesley Courtyards Limited | Real estate | 2004 |
| Apsley & Wellesley Management Limited | Real estate | 2004 |
| Aquila Property (London) Limited | Extraterritorial | 2009 |
| Aquila Property Group Limited | Professional & scientific | 2009 |
| Aquila Property Search Limited | Extraterritorial | 2009 |
| Aralia Court Management Co. Limited | Households | 1981 |
| Aralia Systems Limited | Information & communication | 1996 |
| Aray Content Ltd | Professional & scientific | 2024 |
| ARC. Dogwear Ltd | Wholesale & retail | 2025 |
| Archetech Media Ltd | Information & communication | 2010 |
| Archie's Fish & Chips Ltd | Hospitality | 2019 |
| Archies Minster Ltd | Hospitality | 2023 |
| Aria Coaching Limited | Health & social care | 2025 |
| Arklow Freehold Limited | Households | 2025 |
| Arnold Brothers Contracting Limited | Manufacturing | 2017 |
| Aron Consulting Ltd | Professional & scientific | 2020 |
| ARP Entertainment Ltd | Arts & recreation | 2025 |
| Arquero Law LLP | | 2025 |
| Arrow Carpentry & Joinery Ltd | Construction | 2018 |
| ART4USTUDIO Limited | Extraterritorial | 2004 |
| Artist Partners Limited | Arts & recreation | 1951 |
| Artusi (Deptford) Limited | Extraterritorial | 2016 |
| Artusi (Peckham) Limited | Hospitality | 2013 |
| Artusi Restaurants Limited | Financial services | 2016 |
| ARV Power Ltd | Professional & scientific | 2018 |
| Arvelora Ltd | Wholesale & retail | 2026 |
| Asel's Treasure Ltd | Wholesale & retail | 2026 |
| ASH Construction Group Rail Systems Ltd | Construction | 2021 |
| ASH Workman Limited | Information & communication | 2016 |
| Asha Aesthetics Ltd | Health & social care | 2023 |
| Ashworth Assemble Ltd | Construction | 2021 |
| Asobitech Ltd | Information & communication | 2018 |
| ASP Payments Ltd | Wholesale & retail | 2025 |
| Aspen Vision Ltd | Administrative & support | 2025 |
| ASQ Partners II Ltd | Real estate | 2023 |
| ASQ Partners III Ltd | Real estate | 2024 |
| ASQ Partners IV Ltd | Real estate | 2025 |
| ASQ Partners Ltd | Real estate | 2022 |
| Assisted Living Services (Kent) Limited | Health & social care | 2014 |
| Assistive Tuition Limited | Education | 2018 |
| Association of Tour Managers (UK) Limited(The) | Other services | 1975 |
| Associative Trails Limited | Information & communication | 2005 |
| Aster UK Limited | Professional & scientific | 2008 |
| Astera Global Limited | Other services | 2019 |
| Astoria Management Ltd | Transport & logistics | 2023 |
| ASV Design Limited | Professional & scientific | 2023 |
| Athena Probate Limited | Professional & scientific | 2019 |
| Athenian Properties Limited | Households | 1992 |
| Atlas Fiber Engravings Ltd | Manufacturing | 2025 |
| Atml Drylining Limited | Construction | 2018 |
| Atom Surveyors Ltd | Professional & scientific | 2026 |
| Audacious Marine Boats and Mouldings Limited | Manufacturing | 2019 |
| Audacious Marine Limited | Manufacturing | 2012 |
| Audax Support and Wellbeing Services Ltd | Professional & scientific | 2020 |
| Audax Supported Living Community Interest Company | Professional & scientific | 2019 |
| Augusta Building Ltd | Construction | 2024 |
| Aureus Tree Services Limited | Administrative & support | 2016 |
| AUS Plumbing Services Ltd | Construction | 2022 |
| Autoscot Manpower Limited | Wholesale & retail | 2011 |
| Avaishla Ltd | Other services | 2020 |
| Average Golfers Club Limited | Wholesale & retail | 2025 |
| Avman Engineering Limited | Transport & logistics | 2009 |
| Axis Cloud Accounting Limited | Professional & scientific | 2016 |
| Ayantika Technologies Ltd | Information & communication | 2023 |
| Ayaz & Araz Barbers Limited | Other services | 2023 |
| Ayloo Nexus Ltd | Wholesale & retail | 2025 |