| Action Learning Academy Limited | Professional & scientific | 2015 |
| Acute Medics Ltd | Health & social care | 2015 |
| AD Soft Furnishings Ltd | Construction | 2011 |
| Adamo Energy (UK) Limited | Mining & quarrying | 2007 |
| Adams Rope Inspections Ltd | Professional & scientific | 2022 |
| Adaptiplay CIC | Education | 2024 |
| ADB Electrical Contractors (South Wales) Ltd | Construction | 2022 |
| Addix Fitness Limited | Arts & recreation | 2020 |
| Addix Group Limited | Other services | 2025 |
| Adela Care Limited | Health & social care | 2014 |
| Adfer Natur CIC | Information & communication | 2025 |
| Adrastos Business Support Limited | Professional & scientific | 2018 |
| Adriano's Developments Limited | Real estate | 2023 |
| Adriniko Speed Ltd | Transport & logistics | 2015 |
| Advance Systems Limited | Extraterritorial | 2023 |
| Advanced Computing Solutions Ltd | Wholesale & retail | 2018 |
| Advantage Education Limited | Education | 2023 |
| Advantia Business Solutions Limited | Other services | 1996 |
| Advantia United Business Solutions Limited | Professional & scientific | 2008 |
| Adventure Activities Limited | Arts & recreation | 2003 |
| AE Plastic Reconstructive Surgery Limited | Health & social care | 2022 |
| Aegis Labs Limited | Information & communication | 2025 |
| Aeras Aviation Ltd | Wholesale & retail | 2018 |
| Aero Shuttles Ltd | Transport & logistics | 2025 |
| Aerodot Limited | Professional & scientific | 2014 |
| Aerofix Limited | Manufacturing | 2025 |
| Aerospace Wales Forum Limited | Other services | 2003 |
| Aetherion Energy Ltd | Professional & scientific | 2025 |
| Aevitas Wealth Ltd | Financial services | 2015 |
| Affinity E&D Ltd | Hospitality | 2019 |
| Affordable Tyres 2U Ltd | Extraterritorial | 2023 |
| Africraft Creations Limited | Wholesale & retail | 2025 |
| Afterbeat Coffee Ltd Ltd | Manufacturing | 2023 |
| AGR Electrical Contractors Ltd | Construction | 2023 |
| Ahead of the Game Enterprises Ltd | Education | 2020 |
| AHR Logistics Ltd | Transport & logistics | 2021 |
| AI Clean Robotics & System Limited | Information & communication | 2025 |
| AIM Sports Academy Limited | Arts & recreation | 2016 |
| Airborne Systems Pension Trust Limited | Professional & scientific | 1990 |
| Aircraft Materials Limited | Professional & scientific | 1957 |
| Aircraft Structure Done Ltd | Manufacturing | 2025 |
| Airport Transfers Bridgend Ltd | Transport & logistics | 2017 |
| Airvent Fabrication Ltd. | Manufacturing | 2017 |
| Aisorongon Ltd | Health & social care | 2023 |
| Aitex Services Ltd | Wholesale & retail | 2020 |
| AJ Elec Limited | Manufacturing | 2026 |
| AJ Electrical Partnership Limited | Construction | 2016 |
| AJ Retros Ltd | Wholesale & retail | 2020 |
| AJ Services ( Bridgend) Limited | Construction | 2017 |
| AJ Utility Services Ltd | Other services | 2016 |
| Aj.Safi&Co. Ltd | Construction | 2019 |
| AJJ Property Ltd | Real estate | 2019 |
| AJP Financial Planning Services Limited | Financial services | 2015 |
| AJR Associates Ltd | Professional & scientific | 2021 |
| AJR Rentals Limited | Real estate | 2021 |
| AJT Builders Limited | Construction | 2012 |
| AK & Co Window Installations Limited | Other services | 2019 |
| Al&C LLP | | 2011 |
| Alan Marsh (Taxation) Ltd | Professional & scientific | 2002 |
| Alan T. Brown Limited | Professional & scientific | 1980 |
| Alanya Turkish Barbers Ltd | Other services | 2026 |
| Alcatraz Island Limited | Information & communication | 2018 |
| Alchemy Plus Ltd | Manufacturing | 2018 |
| Aldermark Limited | Professional & scientific | 2018 |
| Aldridge Infrastructure Limited | Wholesale & retail | 2025 |
| Alex Allen Properties Limited | Real estate | 2019 |
| Alex Duckett Limited | Financial services | 2020 |
| Alif Zone Limited | Construction | 2025 |
| Alin Spedition Ltd | Transport & logistics | 2018 |
| Alize Shutters Curtains & Blinds Ltd | Manufacturing | 2021 |
| ALL About Holes Limited | Professional & scientific | 2009 |
| ALL Sculptures Great & Small Ltd | Manufacturing | 2022 |
| ALL2GETHR Industries Ltd | Information & communication | 2010 |
| ALL2GETHR Ltd | Information & communication | 2009 |
| Allcranialmotion Ltd | Construction | 2025 |
| Allen and Company (Industrial Glazing and Painting Specialists) Limited | Manufacturing | 1980 |
| Allen and Partners Limited | Administrative & support | 2002 |
| Allspares (Auto) Investments Limited | Financial services | 2025 |
| Allspares Auto (Holdings) Limited | Professional & scientific | 2015 |
| ALM - Investment Holding Ltd | Financial services | 2019 |
| Almsco Limited | Extraterritorial | 2008 |
| Alon Developments Limited | Real estate | 2021 |
| Alpha and Omega International Church Limited | Information & communication | 2020 |
| Alpine Quantity Surveying Ltd | Professional & scientific | 2022 |
| Altech UK Labelling Technologies Limited | Manufacturing | 2007 |
| Altro Metals Ltd. | Wholesale & retail | 1993 |
| Aluminsulate Ltd | Manufacturing | 2024 |
| AM DRO Pets Ltd | Administrative & support | 2025 |
| Amar Ghattaura Holdings Ltd | Financial services | 2021 |
| Amar Ghattaura Limited | Health & social care | 2012 |
| Amaris Granite & Marble Limited | Manufacturing | 2005 |
| Ambassador Cleaning Services Limited | Other services | 2000 |
| Amber Gold SP Ltd | Transport & logistics | 2022 |
| Amberwell Engineering Services Limited | Manufacturing | 2004 |
| Amberwell Group Limited | Manufacturing | 2025 |
| Ambiance Food Ltd | Hospitality | 2024 |
| Ambiance Kitchen Ltd | Hospitality | 2026 |
| Ambiquire Limited | Administrative & support | 2011 |
| AMD Property Redevelopments Limited | Construction | 2018 |
| Amdani Corneli C.I.C. | Administrative & support | 2026 |