| Agile Internet Limited | Information & communication | 2005 |
| Ahmmed Movers Ltd | Transport & logistics | 2025 |
| Airstream Air Conditioning Ltd | Construction | 2025 |
| Airways Aero Associations Limited | Transport & logistics | 1947 |
| AJ Lowe Business Consultancy Limited | Professional & scientific | 2009 |
| AJW Civil Engineering Limited | Professional & scientific | 2018 |
| AJW Sales Ltd | Wholesale & retail | 2023 |
| Akarna Therapeutics, Ltd | Professional & scientific | 2014 |
| Alarin Property Management Limited | Real estate | 2003 |
| Alastair Mews Management Company Limited | Households | 2008 |
| Alcedo Consulting Ltd | Professional & scientific | 2023 |
| Aldiss & Associates Limited | Administrative & support | 2011 |
| Aldiss Geological Consulting Ltd | Professional & scientific | 2020 |
| Alex D Architects Limited | Professional & scientific | 2014 |
| Alex D Homes Ltd | Real estate | 2022 |
| Alex Jones Home Renovations Limited | Construction | 2025 |
| Alexander Graham Associates Limited | Financial services | 2017 |
| Alexandra Daisy Ginsberg Ltd | Arts & recreation | 2013 |
| Alhambra Services Limited | Real estate | 2016 |
| Alice C L Jones Ltd | Arts & recreation | 2024 |
| Alice in Natureland Ltd | Arts & recreation | 2025 |
| Allergan Holdco UK Limited | Professional & scientific | 2016 |
| Allergan Holdings Limited | Professional & scientific | 1988 |
| Allergan Limited | Wholesale & retail | 1972 |
| Alliance Flexibles Limited | Administrative & support | 2010 |
| Alliance of Independent Events Agencies | Other services | 2017 |
| Alloffer Limited | Professional & scientific | 1993 |
| Allum Consult Limited | Professional & scientific | 2024 |
| Alphatania Limited | Extraterritorial | 2003 |
| Alston Rhodes Ventures Limited | Real estate | 2024 |
| Altinvet Peripatetic Cardiology Specialist Ltd | Professional & scientific | 2025 |
| Alturn Limited | Construction | 2006 |
| Always Hungry Limited | Information & communication | 2023 |
| AM FFF Coaching LLP | | 2025 |
| Ambassador Line Limited | Transport & logistics | 2013 |
| Amezzo Limited | Professional & scientific | 2001 |
| Amicus Therapeutics International Holding Ltd | Health & social care | 2016 |
| Amicus Therapeutics UK Limited | Health & social care | 2005 |
| Amicus Therapeutics UK Operations Limited | Health & social care | 2019 |
| Amiralis Ltd | Arts & recreation | 2021 |
| Amplifyeverything Ltd | Information & communication | 2015 |
| AMR Web Design Ltd. | Information & communication | 2014 |
| Ana's UK Cleaning Services Ltd | Administrative & support | 2025 |
| Anand Corporation UK Ltd | Information & communication | 2011 |
| Anathem Limited | Information & communication | 2023 |
| Anchor Court (Cookham) Residents Limited | Households | 2003 |
| Andy at Work Limited | Professional & scientific | 2015 |
| Andy Burgess Consulting Limited | Professional & scientific | 2024 |
| ANE Holdings Limited | Real estate | 2017 |
| ANE Lettings Limited | Real estate | 2023 |
| Angel Nails Spa Limited | Other services | 2017 |
| Anglo Austrian Limited | Professional & scientific | 2020 |
| Anglo Chalfont Management Ltd | Real estate | 2006 |
| Anglo Chilena Ltd. | Administrative & support | 2003 |
| Angèle Jewellery Ltd | Wholesale & retail | 2021 |
| Anlot Limited | Information & communication | 2008 |
| AON Care Limited | Health & social care | 2026 |
| AP Motors Limited | Wholesale & retail | 2009 |
| Aperta Mente Ltd | Real estate | 2003 |
| Apex Sales Performance Ltd | Professional & scientific | 2025 |
| Apex Signature Metals Ltd | Wholesale & retail | 2026 |
| APH Southfield Limited | Real estate | 2021 |
| Apparel Discount Direct Ltd | Administrative & support | 2016 |
| Apparel Export Ltd | Manufacturing | 2019 |
| Appearance Based Medicine Limited | Health & social care | 2016 |
| Apple Land Estates Limited | Real estate | 2009 |
| Appleton Design Associates Limited | Professional & scientific | 2009 |
| Application Labs Limited | Information & communication | 2019 |
| AQ Business Solutions Ltd | Professional & scientific | 2021 |
| Aquaflow Solutions Limited | Construction | 2011 |
| Aragon Court Limited | Households | 2005 |
| Aragorn S.C. Ltd | Wholesale & retail | 2008 |
| Arbo Biotechnology Limited | Wholesale & retail | 2023 |
| Arcturus Capital Partners Ltd | Professional & scientific | 2024 |
| Ardgowan Homes (Bourne END) Ltd | Construction | 2021 |
| Ardgowan Homes (South East) Ltd | Construction | 2021 |
| Ariel Media Group Limited | Information & communication | 2021 |
| Aries Aviation Management Ltd | Transport & logistics | 2008 |
| Artclubvfx Limited | Professional & scientific | 2019 |
| Artemis Acquico Ltd. | Other services | 2023 |
| Arvn Holdings Ltd | Real estate | 2021 |
| AS YOU Like IT Limited | Professional & scientific | 1997 |
| Ascerta Limited | Information & communication | 2010 |
| Ascot Bespoke Developments Limited | Real estate | 2013 |
| Ascot Residential Homes Limited | Health & social care | 1977 |
| ASH Literary Limited | Information & communication | 2023 |
| Ashfield Property Holdings Limited | Real estate | 2017 |
| Ashfield Wycombe (Buckingham Place) Ltd | Real estate | 2021 |
| Ashfield Wycombe Limited | Real estate | 2019 |
| Ashford Developments Limited | Extraterritorial | 2005 |
| Ashington House Management Limited | Households | 2003 |
| Ashley Hill Multi Academy Trust | Education | 2012 |
| Ashton RIX Limited | Health & social care | 2014 |
| Askett & English Ltd | Manufacturing | 2011 |
| ASM Marlow Limited | Financial services | 2021 |
| Asolvi UK Limited | Information & communication | 1987 |
| Aspen Worldwide Ltd | Administrative & support | 2003 |
| Aspire Resourcing Limited | Administrative & support | 2002 |
| Aspire Sports Management Ltd | Professional & scientific | 2022 |
| Assan Panel UK Limited | Construction | 2023 |