| Amplity Ltd | Professional & scientific | 2008 |
| Amreen - "Faith and Positive Attitude" Limited | Health & social care | 2015 |
| AMS Wealth Management Ltd | Financial services | 2021 |
| Analiya Ltd | Wholesale & retail | 2025 |
| Anand Holdings Limited | Financial services | 2017 |
| Anderson Strategic Marketing Limited | Administrative & support | 2004 |
| Andrew Gabriel Limited | Professional & scientific | 2012 |
| Angel Partners Ltd | Wholesale & retail | 2021 |
| Anjano Limited | Real estate | 2010 |
| Anju Properties Limited | Real estate | 2020 |
| ANN Conway Developments Limited | Construction | 2016 |
| ANN Conway Investments Limited | Real estate | 2016 |
| ANN Hall Consultancy Ltd | Other services | 2016 |
| Annalex Ventures Ltd | Information & communication | 2018 |
| Annesley Ltd | Health & social care | 2021 |
| Annie Hardinge Limited | Information & communication | 2011 |
| ANS Project 1 Limited | Other services | 2019 |
| Anthony David Chapman Company Limited | Transport & logistics | 2011 |
| Anthony Lodge Ltd | Construction | 2012 |
| Antppek Limited | Health & social care | 2012 |
| Anytime Medical Limited | Information & communication | 2008 |
| Aotearoa Seafood Limited | Wholesale & retail | 2025 |
| AP Medical Services (UK) Ltd | Health & social care | 2013 |
| AP SD Sixty One Limited | Wholesale & retail | 2025 |
| Apexhire Recruitment Ltd | Administrative & support | 2024 |
| Aplym Limited | Other services | 2014 |
| Apna Fresh World Foods Limited | Construction | 2024 |
| Appella Consulting Limited | Professional & scientific | 2012 |
| Appila Limited | Professional & scientific | 2004 |
| Appp Ltd | Other services | 2023 |
| Apprenticeship Solutions Limited | Administrative & support | 2011 |
| Appsworks Limited | Information & communication | 2004 |
| APS Effects Ltd | Information & communication | 2026 |
| Aptiq Ltd | Information & communication | 2026 |
| Aqoia Limited | Administrative & support | 2012 |
| ARB Doctors Limited | Health & social care | 2018 |
| Arbortech Tree Surgery Limited | Administrative & support | 2015 |
| Archetypes Growth Ltd | Information & communication | 2021 |
| Archive ZOO Limited | Other services | 2018 |
| Archmo Limited | Real estate | 2023 |
| Arclok Auto Locksmiths Limited | Wholesale & retail | 2025 |
| Ardel Limited | Other services | 2014 |
| Ardmore Accountancy Limited | Professional & scientific | 2021 |
| Ardonis Accounting Solutions Limited | Professional & scientific | 2025 |
| Area 53 Limited | Administrative & support | 2016 |
| Area Homes Limited | Real estate | 2023 |
| Area Management Consulting Limited | Professional & scientific | 2025 |
| Arena Solutions Limited | Construction | 2012 |
| Aretas Healthcare Ltd | Professional & scientific | 2021 |
| Argenx UK Ltd | Wholesale & retail | 2022 |
| Argon Investment Ltd | Real estate | 2020 |
| ARK Psychology and Consultancy Ltd | Education | 2023 |
| Arktecs Solutions Ltd | Information & communication | 2025 |
| Arnies Limited | Wholesale & retail | 2006 |
| Arricchire Limited | Administrative & support | 2011 |
| Arrowhive Equipment Limited | Construction | 1986 |
| Arroyo Himowicz Ltd | Hospitality | 2019 |
| Art Productions TV Film & Media Ltd | Information & communication | 2022 |
| Arthur Davis Ltd | Information & communication | 2018 |
| Artillery Productions Limited | Other services | 2004 |
| Artimaren Holdings Ltd | Financial services | 2025 |
| Artimaren Limited | Construction | 2019 |
| Artistically (SW) Ltd | Wholesale & retail | 2026 |
| Artistically Ltd | Wholesale & retail | 2025 |
| Arveer PVT Ltd | Other services | 2024 |
| AS Global Holdings Ltd | Information & communication | 2017 |
| AS Steadi AS Limited | Other services | 2016 |
| Asar Portfolio Limited | Real estate | 2024 |
| ASB Radiology Services Ltd | Health & social care | 2015 |
| ASC Electronics Limited | Professional & scientific | 2017 |
| Asembl Limited | Manufacturing | 2021 |
| Asenta Aesthetics Ltd | Health & social care | 2014 |
| Asenta Services Ltd | Wholesale & retail | 2022 |
| ASG Imaging Ltd | Health & social care | 2017 |
| Ashanti Consulting Ltd | Professional & scientific | 2016 |
| Ashington Page Limited | Administrative & support | 1997 |
| Ashkan & Shana Ltd | Real estate | 2022 |
| Ashmore Electrical Services Ltd | Construction | 2025 |
| Asofia Resolve Ltd | Professional & scientific | 2017 |
| Aspazia Properties Ltd | Real estate | 2025 |
| Aspect Consulting Limited | Professional & scientific | 2020 |
| Aspect Inventories Limited | Administrative & support | 2023 |
| Aspin Lodge Residents Management Company Limited | Households | 2015 |
| ASQ Capital Limited | Administrative & support | 2014 |
| Assassination Music Promotions Limited | Information & communication | 1998 |
| Asteroid Management Services Limited | Other services | 2010 |
| Aston Brooks International Sandhu & Wurmser Ltd | Financial services | 2013 |
| Aston Cord Energy Services Limited | Construction | 2009 |
| Aston Glass Limited | Manufacturing | 2019 |
| Aston Haven Ltd | Households | 2024 |
| Astons Plumbing & Heating Limited | Extraterritorial | 2009 |
| Astonvfx Limited | Information & communication | 2018 |
| Astralform Limited | Wholesale & retail | 1988 |
| Ateon Ltd | Information & communication | 2018 |
| Atlantic Capital Ltd | Financial services | 2023 |
| Atlantico Advisers Ltd | Professional & scientific | 2016 |
| Atlas Accountancy Limited | Professional & scientific | 2003 |
| ATM Developers Ltd | Construction | 2021 |
| Atom Design & Build Limited | Construction | 2022 |
| Atom Grip Limited | Information & communication | 2023 |