| Artz Ventures Ltd | Wholesale & retail | 2025 |
| AS & Sons Property Ltd | Real estate | 2018 |
| AS Delights Ltd | Wholesale & retail | 2024 |
| AS Good AS New BE Ltd | Wholesale & retail | 2013 |
| AS Plants (Bucks) Ltd | Wholesale & retail | 2026 |
| AS Property Aylesbury Ltd | Real estate | 2024 |
| ASA Rail Ltd | Transport & logistics | 2025 |
| ASA Security Ltd | Administrative & support | 2026 |
| Asante Design Limited | Administrative & support | 2017 |
| Asent Consultancy Ltd | Professional & scientific | 2025 |
| Asghar Real Estate Ltd | Real estate | 2026 |
| ASH Commercial Heli's Ltd | Transport & logistics | 2024 |
| ASH World Enterprises Ltd. | Information & communication | 2003 |
| Ash&Harper Ltd | Arts & recreation | 2020 |
| Asha Ltd | Professional & scientific | 2017 |
| Asha's EYE Clinic Limited | Health & social care | 2025 |
| Ashana Global Ltd | Administrative & support | 2012 |
| Ashbridge Capital Group Limited | Financial services | 2025 |
| Ashburton IT Consultancy Ltd | Information & communication | 2023 |
| Ashby IT Ltd | Information & communication | 2014 |
| Ashclark Ltd | Professional & scientific | 2015 |
| Ashcote Limited | Real estate | 2024 |
| Ashiv Takeaway Ltd | Hospitality | 2025 |
| Ashley & Finch Limited | Real estate | 1999 |
| Ashley & Finch Recruitment Limited | Administrative & support | 2025 |
| Ashley Raines Consultancy Limited | Information & communication | 2024 |
| Ashridge Property Consulting Limited | Real estate | 2012 |
| Asian Delights Ltd | Wholesale & retail | 2016 |
| Asian Grocery Aylesbury Ltd | Wholesale & retail | 2023 |
| Asias Consultancy Ltd | Professional & scientific | 2025 |
| Asiv Lettings Ltd | Real estate | 2022 |
| Asjlc Limited | Financial services | 2011 |
| ASK Accountants & Co UK Ltd | Professional & scientific | 2021 |
| Askyves UK Visa & Information CIC | Administrative & support | 2025 |
| Asma Tattoo and Arts Ltd | Other services | 2026 |
| Asmex Services Limited | Administrative & support | 1996 |
| Asmi Consultancy Ltd. | Professional & scientific | 2014 |
| Asmita & a 3 Limited | Real estate | 2020 |
| Asmita & a 5 Limited | Real estate | 2024 |
| Asmita & a Limited | Construction | 2012 |
| Asp.Sports Ltd | Arts & recreation | 2024 |
| Aspen Financial Solutions Limited | Professional & scientific | 2021 |
| Aspen Residential Limited | Real estate | 2021 |
| Aspire MED Ltd | Education | 2023 |
| Aspire NET Solutions Limited | Information & communication | 2013 |
| Aspire Planning Limited | Information & communication | 2022 |
| Aspireppt Ltd | Construction | 2024 |
| Asquare Digital Limited | Information & communication | 2025 |
| Assured Beef and Lamb Limited | Professional & scientific | 1992 |
| AST Aylesbury Ltd | Wholesale & retail | 2020 |
| Asthetica Ltd | Professional & scientific | 2024 |
| Aston Building Surveyors Ltd | Administrative & support | 2011 |
| Aston Chemicals Limited | Manufacturing | 1990 |
| Aston Commercial Cleaning Ltd | Administrative & support | 2018 |
| Aston Valeting Ltd | Other services | 2026 |
| Astors Resource Limited | Professional & scientific | 2022 |
| Astraea Facilities Management Ltd | Real estate | 2025 |
| Asymmetry Digital Corp Inc Ltd | Wholesale & retail | 2025 |
| Async Software Limited | Information & communication | 2012 |
| AT Carpentry & Cabinetry Limited | Manufacturing | 2020 |
| AT Erudite UK Ltd | Real estate | 2025 |
| At&T Group (UAE) Ltd | Financial services | 2025 |
| Atalay X Ltd | Hospitality | 2025 |
| Atcheson Care Consultancy Ltd | Professional & scientific | 2024 |
| ATD Medical Limited | Health & social care | 2015 |
| Atelier DE Scene Ltd | Manufacturing | 2025 |
| Ateomar Ltd | Construction | 2026 |
| ATF Electrical Limited | Construction | 2017 |
| Athletes in Motion Ltd | Education | 2016 |
| Atlas Cooling Ltd | Manufacturing | 2023 |
| Atobatele UK Limited | Health & social care | 2019 |
| Atom Education Limited | Administrative & support | 2006 |
| Atom Health Limited | Administrative & support | 2010 |
| Atomyc Ltd | Other services | 2023 |
| ATP IT Solutions Limited | Information & communication | 2018 |
| Atpath Ltd | Information & communication | 2025 |
| Atree Homes Limited | Real estate | 2022 |
| Attica Gambling Limited | Arts & recreation | 2011 |
| Attitude to Care Ltd | Health & social care | 2014 |
| Atvb Ltd | Manufacturing | 2015 |
| Atwal Limited | Wholesale & retail | 2023 |
| Audere Talent Management Limited | Arts & recreation | 2018 |
| Audio Logistics Limited | Administrative & support | 2012 |
| Audley Real Estate LLP | | 2016 |
| Augwell Technologies Ltd | Information & communication | 2025 |
| AUK Airport Service Ltd | Transport & logistics | 2020 |
| Aura Body Clinic Ltd | Health & social care | 2026 |
| Aura Candleworks Ltd | Manufacturing | 2025 |
| Aura Online Limited | Administrative & support | 2011 |
| Aura Property Partners Ltd | Construction | 2026 |
| Aura Security Group Holdings Ltd | Financial services | 2025 |
| Aura Security Group Limited | Administrative & support | 2003 |
| Auramagnet Ltd | Professional & scientific | 2025 |
| Auredrian Ltd | Information & communication | 2013 |
| Auria Star Healthcare Ltd | Health & social care | 2020 |
| Aurora Properties Trading Ltd | Real estate | 2024 |
| Ausra Creates Ltd | Professional & scientific | 2022 |
| Aussie Plastering and Construction Limited | Construction | 2015 |
| Austa Ltd | Hospitality | 2024 |
| Austin TEN Drivers' Club Limited | Other services | 1981 |