| Architecturall Management Ltd | Households | 2017 |
| Arclineelectrical Ltd | Construction | 2025 |
| Arctic Flooring Ltd | Construction | 2025 |
| Arctive Solutions Ltd | Information & communication | 2017 |
| Arden Housing Ltd | Real estate | 2025 |
| Ardleigh Court RTM Company Limited | Households | 2017 |
| Areeya Limited | Wholesale & retail | 2025 |
| Arflo Ltd | Construction | 2023 |
| Argun 20 Ltd | Hospitality | 2018 |
| Argyle Decorating Ltd | Construction | 2022 |
| Ariadne Services Limited | Other services | 2026 |
| Arinium Limited | Real estate | 2019 |
| ARK Film Distribution Ltd | Information & communication | 2026 |
| Armco Asset Management Limited | Financial services | 2022 |
| Armco Lighthouse Lettings Limited | Real estate | 2022 |
| Armco Lighthouse Limited | Real estate | 2021 |
| Arne Consultancy Limited | Professional & scientific | 2021 |
| Arney Ltd | Construction | 2024 |
| ARO1 Ltd | Other services | 2024 |
| Arran Support Limited | Health & social care | 2020 |
| Arrowstar Limited | Other services | 2014 |
| Arsar Limited | Hospitality | 2024 |
| Arsim Tech Limited | Information & communication | 2024 |
| Arslan Fish & Chips Ltd | Hospitality | 2026 |
| Art & Restoration Djidjev Ltd | Construction | 2023 |
| Art Infrastructure Limited | Real estate | 2021 |
| Artash Property Ltd | Real estate | 2021 |
| Artha Management Solutions Limited | Information & communication | 2011 |
| Arthur J Ltd | Real estate | 2020 |
| Artisan Acquisitions Limited | Real estate | 2021 |
| Artisan Design & Build Limited | Construction | 2000 |
| Artisan Pipework Ltd | Construction | 2010 |
| Artk Production Ltd | Information & communication | 2023 |
| Arturiane Limited | Real estate | 2021 |
| Artwork by Amanda Limited | Arts & recreation | 2015 |
| Artx Meta Ltd | Administrative & support | 2024 |
| Aruman Ltd | Households | 2021 |
| Arunasv Transport Ltd | Transport & logistics | 2024 |
| Arundel Home Improvements Ltd | Construction | 2010 |
| ARW Heating & Plumbing Ltd | Construction | 2012 |
| ARW Carpentry and Joinery Limited | Construction | 2023 |
| Arwd Limited | Construction | 2019 |
| ARX Homes Limited | Real estate | 2025 |
| Arya Consultancy Services Ltd | Education | 2024 |
| Arya London Ltd | Hospitality | 2019 |
| AS Alexander Group Limited | Manufacturing | 2016 |
| AS Garden Solutions Limited | Administrative & support | 2025 |
| AS Plumbing and GAS (London) Limited | Construction | 2014 |
| AS Project Management Ltd | Construction | 2020 |
| Asav Limited | Financial services | 2023 |
| Asbestos Management Group Ltd | Professional & scientific | 2020 |
| Asbestos Waste Solutions Limited | Water & waste | 2013 |
| Ascendant Manufacturing Solutions Limited | Professional & scientific | 2012 |
| Ascent UK Building Services Ltd | Construction | 2018 |
| ASG- Alcohol Support Group- Orpington Community Interest Company | Health & social care | 2025 |
| ASH Breakdown Recovery Ltd | Transport & logistics | 2024 |
| ASH Bros Limited | Real estate | 2025 |
| ASH Kebab House Ltd | Hospitality | 2021 |
| ASH Kitchen and Bakers Ltd | Hospitality | 2024 |
| Ashdown Business Developments Ltd | Professional & scientific | 2025 |
| Ashfield Place Residents Limited | Households | 1995 |
| Ashleigh Limited | Construction | 2008 |
| Ashleigh Shea Photography Ltd | Professional & scientific | 2017 |
| Ashmika Shan Ltd | Wholesale & retail | 2024 |
| Ashrose Drainage Limited | Construction | 2002 |
| Ashurst Construction and Maintenance Limited | Construction | 2023 |
| ASK an OT Limited | Health & social care | 2010 |
| ASK Business Services Limited | Professional & scientific | 2008 |
| ASK Financial Planning Ltd | Professional & scientific | 2025 |
| ASM Global Limited | Administrative & support | 2023 |
| ASM Planning Consultancy Limited | Professional & scientific | 2005 |
| Asma Properties Ltd | Real estate | 2020 |
| Asma Tech Solutions Limited | Information & communication | 2016 |
| Asmec FM Limited | Construction | 2024 |
| Asmec Group Limited | Financial services | 2026 |
| Asmec Limited | Construction | 2012 |
| Asmi London Ltd | Wholesale & retail | 2021 |
| Asota Services Limited | Health & social care | 2014 |
| ASP Shareholdings Limited | Wholesale & retail | 2019 |
| Aspendos Dover Kent Ltd | Hospitality | 2017 |
| Aspendos West Terrace Ltd | Hospitality | 2017 |
| Aspinall Hair Limited | Other services | 2023 |
| Aspiration for ALL Cooperative Trust | Education | 2018 |
| Aspire Control Ltd | Mining & quarrying | 2016 |
| Aspire Operations Consultancy Ltd | Professional & scientific | 2021 |
| ASQ Construction Services Limited | Education | 2017 |
| ASQ Development and Training Services Ltd | Education | 2025 |
| ASQ Recruitments Limited | Other services | 2017 |
| Assist Education Ltd | Education | 2021 |
| Association of Super Recognisers Limited | Other services | 2017 |
| Assured Automotive Group Ltd | Wholesale & retail | 2026 |
| Astal Services Limited | Construction | 2021 |
| Astral Propco Limited | Real estate | 2025 |
| Asunta Managements UK Ltd | Administrative & support | 2026 |
| AT8 Capital Partners LLP | | 2019 |
| ATB Construction Ltd | Construction | 2021 |
| ATB Group Holdings Ltd | Financial services | 2025 |
| ATB Propery Investment Ltd | Real estate | 2025 |
| Atchinson Aggregates Ltd | Manufacturing | 2024 |
| Aterr Ltd | Real estate | 2025 |