| Adrian Kidman Plumbing & Heating Limited | Construction | 2012 |
| ADV Leisure Ltd | Administrative & support | 2018 |
| Advantage Flight Support Stansted Ltd | Transport & logistics | 2021 |
| Adventurous Holdings Limited | Financial services | 2024 |
| Aegra Limited | Information & communication | 2025 |
| AER Maven Holdings Limited | Financial services | 2025 |
| Aerospace Manufacturing Limited | Manufacturing | 2018 |
| Aerostrike Ltd | Manufacturing | 2024 |
| AF47 Trading AS the Party Box Ltd | Wholesale & retail | 2023 |
| AFF Productions Ltd | Information & communication | 2018 |
| AGAF3D Ltd | Professional & scientific | 2023 |
| Agntic Ltd | Information & communication | 2025 |
| Agrawal Surgery Ltd | Health & social care | 2023 |
| AGS Corporate Trustees Limited | Professional & scientific | 2020 |
| Ahakista Limited | Real estate | 2026 |
| AHD Engineering Limited | Professional & scientific | 2018 |
| AHG Hotel & Resort Ltd | Administrative & support | 2018 |
| Ahua! Aviation Services Limited | Professional & scientific | 2021 |
| Aionequine Limited | Arts & recreation | 2018 |
| Air Purity Ltd | Professional & scientific | 2020 |
| Aircraft Management Services Ltd | Professional & scientific | 2011 |
| Airvailability Limited | Extraterritorial | 2020 |
| AJ Arnold Logistics Ltd | Transport & logistics | 2021 |
| AJB Media Group Limited | Administrative & support | 2025 |
| AJS Design & Production Services Ltd | Professional & scientific | 2005 |
| AK47 Consultancy Ltd | Professional & scientific | 2020 |
| Akana Collective Ltd | Manufacturing | 2020 |
| Alayna Cullen Ltd | Professional & scientific | 2018 |
| Albany Business Consulting Ltd | Professional & scientific | 2014 |
| Albion-Rose Limited | Professional & scientific | 2018 |
| Alec Rayner Holdings Limited | Real estate | 1962 |
| Alex Dodman Ltd | Manufacturing | 2016 |
| Alex North Consulting Limited | Professional & scientific | 2024 |
| Alfs Driving School Ltd | Education | 2024 |
| Alimentary Innervations Limited | Health & social care | 2009 |
| ALL Auto Solutions Ltd | Wholesale & retail | 2022 |
| Allan Mechanical Ltd | Construction | 2021 |
| Alliance Intelligent Properties Ltd | Real estate | 2026 |
| Alliance Intelligent Scaffolding Ltd | Construction | 2011 |
| Allied Restorations Ltd | Wholesale & retail | 2023 |
| Allsetin Ltd | Administrative & support | 2018 |
| Alma Business Consulting Ltd | Other services | 2025 |
| Alphubel Ltd | Professional & scientific | 2020 |
| Alva Capital LLP | | 2014 |
| AM Shop and Fuel Ltd | Wholesale & retail | 2017 |
| AMA Artisan Bakery Ltd | Manufacturing | 2025 |
| Amanda Murray Design Limited | Administrative & support | 2002 |
| Amandla Academic UK Ltd | Information & communication | 2020 |
| Amandla UK Ltd | Other services | 2019 |
| Amberden Associates Ltd | Professional & scientific | 2021 |
| Amberley Consulting & Co. Ltd | Professional & scientific | 2016 |
| Ambis Resourcing Limited | Administrative & support | 2026 |
| Ambleside Leisure Corner Ltd | Wholesale & retail | 2025 |
| Amelie Gerard Ltd | Professional & scientific | 2026 |
| Ameora Ltd | Wholesale & retail | 2024 |
| Amim Ltd | Real estate | 2019 |
| Amos Consulting Services Ltd | Information & communication | 2023 |
| AMS Industrial Ecology Limited | Water & waste | 2014 |
| AN Ltd | Extraterritorial | 2009 |
| Ananta Thai Food Limited | Hospitality | 2012 |
| Anderson Sharp Ltd | Construction | 2023 |
| Andrew Armour Limited | Administrative & support | 2009 |
| Andrew Jenkins Limited | Professional & scientific | 2004 |
| Andy Lines Communications Limited | Extraterritorial | 2006 |
| Andy's Garden and Aviaries Ltd | Wholesale & retail | 2013 |
| Angel Interiors U.K. Limited | Arts & recreation | 1989 |
| Anglia Building Co. Limited | Wholesale & retail | 2001 |
| Anglia Building Suppliers Limited | Wholesale & retail | 1964 |
| Angus Cook Holdings Limited | Real estate | 2010 |
| Anjulie Van DEN Berg Limited | Health & social care | 2022 |
| Annabel Nichols Ltd | Administrative & support | 2026 |
| Annalogic Limited | Arts & recreation | 2001 |
| Anne Curry Sculpture Ltd | Arts & recreation | 2017 |
| Antbits Limited | Professional & scientific | 2009 |
| Anthony Marcos Limited | Professional & scientific | 2002 |
| Antiqui-Fi Ltd | Information & communication | 2023 |
| Apex Business Consulting Limited | Wholesale & retail | 2021 |
| Apex Dept Collection Limited | Administrative & support | 2026 |
| Apex Development Consultancy Ltd | Professional & scientific | 2024 |
| Apex Estates & Energy Ltd | Construction | 2026 |
| Apex Sponsorship Agency Limited | Information & communication | 2025 |
| Apex Talent Matchmaking Limited | Administrative & support | 2025 |
| APG Payroll Ltd | Professional & scientific | 2023 |
| Aphra Studio Ltd | Information & communication | 2023 |
| Apolina Limited | Wholesale & retail | 2020 |
| Apolina Studio Ltd | Wholesale & retail | 2025 |
| Apollo Associates | | 1969 |
| Apple & Bean Ltd | Arts & recreation | 2022 |
| Applied Ionics Limited | Water & waste | 2000 |
| Appollo Security Services Limited | Administrative & support | 2006 |
| Aptus Capital Ltd | Financial services | 2019 |
| Aptus Capital Mortgage Group Ltd | Financial services | 2025 |
| Aquarius Piercings Ltd | Other services | 2023 |
| Arbicon ADR Limited | Professional & scientific | 2006 |
| ARC CGI Limited | Information & communication | 2011 |
| ARC UK Consulting Limited | Information & communication | 2024 |
| Archers (Grove Road) Management Limited | Real estate | 2005 |
| Archers (Haysoms Close) Management Limited | Real estate | 2006 |
| Archers Developments Ltd | Construction | 2005 |
| Arecor Therapeutics PLC | Financial services | 2021 |