| ATR Property Services Ltd | Construction | 2025 |
| Atrium Architecture Ltd | Professional & scientific | 2020 |
| Atrium CONSTRUCTION2022 Ltd | Construction | 2022 |
| Atrium Ecology Limited | Professional & scientific | 2025 |
| Atrium Planning Consultants Limited | Professional & scientific | 2020 |
| Attic Wardrobe Ltd | Wholesale & retail | 2002 |
| Attica Retail (Wales) Ltd | Wholesale & retail | 2009 |
| AU Vodka Ltd | Wholesale & retail | 2015 |
| Audio Peak Recordings Ltd | Information & communication | 2025 |
| Audioclassroom Ltd | Information & communication | 2025 |
| Audioscope Europe Limited | | 1987 |
| AUR Cymru Property Maintenance Ltd | Households | 2020 |
| AUR Y Ddraig Ltd | Agriculture & fishing | 2018 |
| Aura Yachting Ltd | Manufacturing | 2021 |
| Auralis Medico-Legal Limited | Health & social care | 2025 |
| Aureon Acoustics Ltd | Wholesale & retail | 2026 |
| Aureum Global Ltd | Information & communication | 2025 |
| Aurio Property Group Ltd | Real estate | 2026 |
| Aurmine Limited | Wholesale & retail | 2017 |
| Aurora & Koda Ltd | Education | 2025 |
| Aurora Electrical & Maintenance Ltd | Construction | 2026 |
| Aurora Energy Consulting Ltd | Construction | 2020 |
| Aurora GAS Ltd | Construction | 2015 |
| Aurous Bidco Limited | Financial services | 2023 |
| Aurous Midco Limited | Financial services | 2023 |
| Aurous Topco Limited | Financial services | 2023 |
| Aurrence Beauty & Alliance Limited | Wholesale & retail | 2025 |
| Austin & James Developments Ltd | Real estate | 2020 |
| Austin Diment Joinery Ltd | Construction | 2023 |
| Austin Morris Automotive Company Ltd | Wholesale & retail | 2025 |
| Austin Poole Limited | Real estate | 2025 |
| Authentech Ltd | Information & communication | 2015 |
| Authentic Biryani Bites Limited | Hospitality | 2026 |
| Authentic Japanese Foods Limited | Hospitality | 2015 |
| Autism Fledglings Limited | Education | 2014 |
| Autism Skills Development and Employment Support CIC | Administrative & support | 2010 |
| Auto Services Pontypool Ltd | Wholesale & retail | 2019 |
| Autodor Limited | Construction | 2008 |
| Autofitclothing Ltd | Extraterritorial | 2025 |
| Autofluids Limited | Manufacturing | 2020 |
| Autofluidz Limited | Manufacturing | 2020 |
| Automagic Doors Ltd | Wholesale & retail | 2025 |
| Automated Europe Limited | Wholesale & retail | 2026 |
| Autopay Protocol Ltd | Information & communication | 2026 |
| Autosure Swansea Ltd | Wholesale & retail | 2025 |
| Autovity Tech Ltd | Wholesale & retail | 2026 |
| Auva Properties Group Ltd | Real estate | 2025 |
| AV Installations Ltd | Professional & scientific | 2018 |
| Avallan Limited | Professional & scientific | 2025 |
| Avalon Architecture Limited | Professional & scientific | 2024 |
| Avamtex Solutions Ltd | Other services | 2022 |
| Avanni Kitchens Ltd | Administrative & support | 2022 |
| Avarix Highways Engineering Limited | Construction | 2025 |
| Avarix Limited | Construction | 2025 |
| Avernakis Ltd | Construction | 2022 |
| Averroesa SPV Ltd | Real estate | 2021 |
| Avery Naylor Ltd | Professional & scientific | 2007 |
| Aviation Media Limited | Information & communication | 2011 |
| Avid Construction Ltd | Construction | 2004 |
| Avies (City Developments) Limited | Construction | 2016 |
| Aviles Properties Ltd | Real estate | 2019 |
| Avis Elite Consultants Limited | Professional & scientific | 2021 |
| Avit Structures Limited | Construction | 2017 |
| Avium Financial Limited | Financial services | 2023 |
| AVL Solutions Limited | Manufacturing | 2012 |
| AW Brickwork Ltd | Construction | 2020 |
| Awads Pyramids UK Limited | Wholesale & retail | 2017 |
| AWC Group Limited | Professional & scientific | 2019 |
| AWE Aluminium Ltd | Manufacturing | 2018 |
| Awel Y Coed Management Company Limited | Households | 2012 |
| Awel-Y-Mor Properties Limited | Real estate | 2023 |
| Awen Crane Services Limited | Administrative & support | 2023 |
| Awenid Ltd | Administrative & support | 2010 |
| AWG Investments Limited | Transport & logistics | 2003 |
| Awrb Solar & Storage Solutions Ltd | Construction | 2023 |
| AWS Tree Surgery Limited | Administrative & support | 2016 |
| Awyer Ltd | Wholesale & retail | 2026 |
| Axel Hospitality Limited | Real estate | 2017 |
| Axiom Life Ltd | Financial services | 2019 |
| Axiomlayer Ltd | Information & communication | 2026 |
| Axira Group Ltd | Wholesale & retail | 2025 |
| Axis (Phase 2) Management Company Limited | Real estate | 2005 |
| Axisone Retail Ltd | Wholesale & retail | 2026 |
| Axium Process Limited | Manufacturing | 2002 |
| Axllrod Ltd | Extraterritorial | 2017 |
| Axsis Restaurant Limited | Hospitality | 2025 |
| Ayaans Property Limited | Real estate | 2025 |
| Ayan&Dony Ltd | Transport & logistics | 2018 |
| AYDIN23 Limited | Hospitality | 2025 |
| Aylas Spice Ltd | Hospitality | 2026 |
| Aylecare Limited | Health & social care | 2002 |
| Ayles & Moore Homes Limited | Construction | 2019 |
| Ayles M.E.C Ltd | Construction | 2023 |
| Aylesb Limited | Real estate | 2023 |
| Aynki Family Shopper Ltd | Wholesale & retail | 2023 |
| Ayovine Limited | Administrative & support | 2025 |
| Aysusa Group Limited | Construction | 2023 |
| Azizi Barbers Ltd | Other services | 2018 |
| Aztec Estates Limited | Real estate | 2007 |
| Aztec Gold Limited | Financial services | 2009 |