| Aphex Automate Ltd | Information & communication | 2024 |
| API First Ltd | Professional & scientific | 2021 |
| APL Medical Limited | Administrative & support | 2025 |
| APM Property Ventures Limited | Real estate | 2025 |
| Apple Strawberry Consulting Limited | Professional & scientific | 2024 |
| Apple Window Blinds Limited | Wholesale & retail | 2011 |
| Apprentify Group Limited | Professional & scientific | 2018 |
| Apprentify Limited | Administrative & support | 2016 |
| APR Corporation UK Ltd | Wholesale & retail | 2025 |
| Apricity Capital Ltd | Professional & scientific | 2021 |
| Aprylandrose Limited | Wholesale & retail | 2016 |
| Aptien Limited | Information & communication | 2023 |
| Apugh Consulting Ltd | Information & communication | 2022 |
| Aqua Fire Protection Ltd | Construction | 2020 |
| Aquasys Aeration Consultants Limited | Administrative & support | 2016 |
| Aquateck Ltd | Wholesale & retail | 2021 |
| AR Ward Ltd | Real estate | 2011 |
| Arariel Limited | Real estate | 2024 |
| Arbour Tide Limited | Wholesale & retail | 2006 |
| Arcadian Accounting & Consultancy Limited | Professional & scientific | 2018 |
| Arcane Assets Limited | Administrative & support | 2023 |
| Archfield Medical Limited | Health & social care | 2016 |
| Architeam AI Ltd | Administrative & support | 2024 |
| Arclid Car Sales Ltd | Wholesale & retail | 2023 |
| Arden Park (Redditch) Management Company Limited | Households | 2024 |
| Arete Living Ltd | Real estate | 2024 |
| Arete Virtus Limited | Health & social care | 2026 |
| Argomed Limited | Health & social care | 2012 |
| Argosy Technical Services Limited | Public administration | 2021 |
| Arhj Limited | Professional & scientific | 2014 |
| Aria Tech Investments Limited | Financial services | 2023 |
| Ariadne Software Limited | Information & communication | 2000 |
| ARJ Photography Ltd | Professional & scientific | 2009 |
| Arkal Limited | Professional & scientific | 2017 |
| Arkidder Limited | Information & communication | 2021 |
| Arlanza Advisory Ltd | Professional & scientific | 2015 |
| Arley Foods Limited | Hospitality | 2020 |
| Arley Group Limited | Financial services | 2020 |
| Armadillo Ventures Limited | Real estate | 2020 |
| Armstrong KER (Macclesfield) Limited | Financial services | 1995 |
| Armstrong Private Equity Ltd | Financial services | 2025 |
| Arnage Partners Ltd | Administrative & support | 2020 |
| Arrive Without Travelling Limited | Information & communication | 2021 |
| Arthur Royle Limited | Real estate | 1955 |
| Artico Projects Ltd. | Construction | 2020 |
| Artience UK Limited | Professional & scientific | 2020 |
| Artificially Clear Limited | Education | 2026 |
| ARUBQADIR99 Limited | Administrative & support | 2025 |
| Arvaan Ltd | Information & communication | 2024 |
| Arvind & Suzi Investments Ltd | Real estate | 2023 |
| Arvira Limited | Real estate | 2025 |
| Arvun Limited | Extraterritorial | 2017 |
| AS Cardiology Limited | Health & social care | 2020 |
| ASA Experts Ltd | Professional & scientific | 2025 |
| Ascend Investment Capital Ltd | Financial services | 2025 |
| Ascend Organisational Excellence Limited | Professional & scientific | 2020 |
| Ascendis Accountants, Business & Tax Advisors Ltd | Professional & scientific | 2004 |
| Ascendis Audit Limited | Professional & scientific | 2021 |
| Ascendis Capital Ltd | Financial services | 2025 |
| Ascendis Corporate Advisory Limited | Professional & scientific | 2025 |
| Ascendis Group Limited | Financial services | 2004 |
| Ascendis Intermediaries Ltd | Financial services | 2014 |
| Ascent Lifting Ltd | Construction | 2025 |
| Asean Trade Direct Ltd | Administrative & support | 2008 |
| Ashfield Developments Cheshire Limited | Construction | 2022 |
| Ashford Alderley Limited | Extraterritorial | 2013 |
| Ashtab Properties Ltd | Real estate | 2025 |
| Ashton Registry Services Ltd | Public administration | 2012 |
| Ashworth Medical Ltd | Health & social care | 2019 |
| Asisurg Limited | Health & social care | 2023 |
| ASM Developed Ltd | Construction | 2023 |
| ASP Dental Ltd | Health & social care | 2025 |
| Aspect Civils and Groundworks Limited | Construction | 2024 |
| Aspect Financial Solutions Ltd | Financial services | 2007 |
| Aspect Properties Limited | Real estate | 2015 |
| Asperspec Construction Limited | Construction | 2025 |
| Aspinall Academy of Dance Limited | Arts & recreation | 2006 |
| Aspira Invest Limited | Construction | 2025 |
| Aspire Executive Search Ltd | Administrative & support | 2011 |
| Asset Ecology Ltd | Professional & scientific | 2022 |
| Association of Zimbabwean Pharmacists Abroad CIC | Health & social care | 2021 |
| Assured Pharmacy Ltd | Wholesale & retail | 2014 |
| Astbury Place Management Company Limited | Households | 2014 |
| Astbury Place Management Company NO. 2 Limited | Households | 2016 |
| Astbury T.V.Aerials Limited | Wholesale & retail | 1970 |
| Aston Estates (Berkshire) Limited | Real estate | 2018 |
| Astonville Consultants Limited | Health & social care | 2017 |
| Astra Concepts Ltd | Information & communication | 2021 |
| Astratek Limited | Information & communication | 2018 |
| Astro Food Limited | Hospitality | 2025 |
| Astute Accountancy Services Limited | Professional & scientific | 2018 |
| ASW Electrical & Engineering Ltd | Manufacturing | 2025 |
| AT & SA Holdings Ltd | Financial services | 2025 |
| Atam Distributions Ltd | Wholesale & retail | 2026 |
| ATB Medical Limited | Other services | 2023 |
| Atcg Limited | Professional & scientific | 2023 |
| Atelier Ninety Five Ltd | Wholesale & retail | 2023 |
| Athanis Creative Ltd | Information & communication | 2024 |
| Athelis Group Ltd | Professional & scientific | 2024 |
| Athena Hand and Plastic Surgery Ltd | Health & social care | 2024 |