| Amelliam Limited | Financial services | 2025 |
| American Dance School Ltd | Administrative & support | 2017 |
| AMG Nutrition Limited | Agriculture & fishing | 2010 |
| Amjay Technologies Ltd | Information & communication | 2013 |
| Amos Hospitality Limited | Hospitality | 2024 |
| Analytical Services International Limited | Professional & scientific | 1992 |
| Andersey Close Management Limited | Other services | 2024 |
| Andersey Farm Ltd | Agriculture & fishing | 1999 |
| Andrew Alder Associates Limited | Professional & scientific | 2007 |
| Andrew Watts Limited | Professional & scientific | 2013 |
| Andrews Engineering Limited | Construction | 2025 |
| Andy Yates Ltd | Construction | 2012 |
| Angel Wilkins LLP | | 2009 |
| Anouk Video Production Ltd | Information & communication | 2018 |
| Anox Plus Limited | Extraterritorial | 2024 |
| Antigo MHB Breakers Ltd | Construction | 2002 |
| Antonio Neves Ltd | Information & communication | 2017 |
| Antrum Partners Limited | Professional & scientific | 2013 |
| Anvower Advisory Ltd | Information & communication | 2025 |
| Anytime Car Delivery Services Ltd | Wholesale & retail | 2023 |
| Apex Books Ltd | Professional & scientific | 2024 |
| Appel Tree Family Holdings Ltd | Wholesale & retail | 2025 |
| Apple Tree Accountancy Ltd | Professional & scientific | 2008 |
| Applied Computer Music Technologies Ltd | Information & communication | 2013 |
| APT Planning Limited | Construction | 2008 |
| Aquablue Plumbing & Heating Ltd | Construction | 2026 |
| Aquity Acceleration Limited | Information & communication | 2015 |
| Arandar Limited | Professional & scientific | 2003 |
| Arboricare Consultancy Ltd | Agriculture & fishing | 2022 |
| Arcimboldo Productions Limited | Information & communication | 2002 |
| Ardington House Ltd | Arts & recreation | 1998 |
| Argo Irrigation Ltd | Other services | 2014 |
| Arlington Development Management Limited | Financial services | 2024 |
| Armox Legacy Limited | Financial services | 2025 |
| Arnfield Limited | Wholesale & retail | 1983 |
| Arnoldsf Limited | Professional & scientific | 2020 |
| Arrange My Travel Limited | Administrative & support | 2016 |
| Art Check Ltd | Administrative & support | 2010 |
| Artch Consultancy Ltd | Other services | 2024 |
| Articulation Avenue Limited | Wholesale & retail | 2025 |
| Artisan Estate Management Limited | Real estate | 2009 |
| Artworkio Ltd | Information & communication | 2021 |
| AS & DL Limited | Hospitality | 2012 |
| ASH Black Tattoo Limited | Other services | 2025 |
| ASH MAY PT Ltd | Arts & recreation | 2023 |
| Ashthorn Consulting Limited | Information & communication | 2001 |
| ASK Auto Repair Ltd | Wholesale & retail | 2025 |
| ASK Empo Ltd | Information & communication | 2024 |
| ASK Property Holding Limited | Households | 2016 |
| Aspen Waite South Limited | Professional & scientific | 2019 |
| Assessment in Care Limited | Construction | 2000 |
| Association for Clinical Data Management Limited | Other services | 2001 |
| Astromarine Ltd | Professional & scientific | 2025 |
| Astrosystems Limited | Wholesale & retail | 1998 |
| AT Automotive Ltd | Wholesale & retail | 2019 |
| AT UK Stays Ltd | Administrative & support | 2025 |
| Athagoras Aquico UK-01 Limited | Financial services | 2024 |
| Athena Accountants & Business Advisors Ltd | Professional & scientific | 2017 |
| Atlas Automated Services Ltd | Agriculture & fishing | 2024 |
| Atlas Express Cleaning Ltd | Administrative & support | 2021 |
| Atomic Precision Ltd | Professional & scientific | 2019 |
| ATR Consultants Ltd | Professional & scientific | 2017 |
| Aubergine PUB Co Ltd | Hospitality | 2025 |
| Auclum Construction Limited | Construction | 2009 |
| Auclum Properties Limited | Construction | 2002 |
| Augmented Hype Ltd | Professional & scientific | 2022 |
| Aukan Engineering Ltd | Professional & scientific | 2025 |
| Aurox Clothing Ltd | Wholesale & retail | 2025 |
| Autodiscovery Ltd. | Wholesale & retail | 2020 |
| Autofix by Matt Limited | Wholesale & retail | 2025 |
| Automotion Productions Limited | Information & communication | 2009 |
| Autosportif Engineering Limited | Wholesale & retail | 2014 |
| AV8OR IP Limited | Administrative & support | 2017 |
| AV8OR Limited | Professional & scientific | 2007 |
| Avenue Heritage Limited | Administrative & support | 2026 |
| Aviosphere Ltd | Transport & logistics | 2023 |
| Avitical Limited | Wholesale & retail | 2019 |
| Avitical Properties Limited | Real estate | 2024 |
| AWC Benta Limited | Professional & scientific | 2012 |
| Awkward Films Ltd | Arts & recreation | 2009 |
| Axis (Milton) Limited | Professional & scientific | 1995 |
| Axis Plant Services Limited | Administrative & support | 2024 |
| Axone Systems Ltd | Information & communication | 2010 |
| B B Logs Limited | Wholesale & retail | 2025 |
| B Horizon Ltd | Professional & scientific | 2025 |
| B&L Cars Ltd | Wholesale & retail | 2019 |
| Baby Legs Grips Limited | Information & communication | 2026 |
| Balaclava Consulting Ltd | Professional & scientific | 2011 |
| Balaj Enterprises Ltd | Wholesale & retail | 2024 |
| Balaton Investments Limited | Real estate | 2023 |
| Balria Ltd | Wholesale & retail | 2021 |
| Bambam Products Ltd | Manufacturing | 2022 |
| Bampton Close Residents Association Limited | Households | 1994 |
| Banktop Securities Limited | Real estate | 1983 |
| Barney Wilkinson Ltd | Information & communication | 2006 |
| Barrel House Productions Limited | Administrative & support | 2021 |
| Bass Therapy Ltd | Wholesale & retail | 2021 |
| Bassett & Co (Wantage) Limited | Hospitality | 2016 |
| Bassett Spirits Ltd | Hospitality | 2022 |
| Battle Badger Logistics Ltd | Transport & logistics | 2024 |