| Aquabullet Ltd | Manufacturing | 2025 |
| Aquagas Heating & Plumbing Ltd | Construction | 2015 |
| Aqualogic Limited | Professional & scientific | 2002 |
| Aquatech Plumbing Services Ltd | Construction | 2016 |
| Aquathin UK Ltd | Water & waste | 2019 |
| Aracap International Limited | Administrative & support | 2015 |
| Arachny Ltd | Information & communication | 2015 |
| Aral Bicycle Ltd | Manufacturing | 2026 |
| Arawak Ltd | Professional & scientific | 2010 |
| Arbington Management Services Limited | Administrative & support | 2019 |
| ARC7 Estates Ltd | Real estate | 2023 |
| Arcarius Laboratories Ltd | Professional & scientific | 2024 |
| Arch Property Ltd | Construction | 2015 |
| Archatech Limited | Professional & scientific | 2004 |
| Arche Consortia UK Limited | Administrative & support | 2021 |
| Archer Electrical Ltd | Construction | 2020 |
| Archer Investment Group Limited | Real estate | 2024 |
| Archer Strategy Ltd | Professional & scientific | 2026 |
| Archers Antique Restorations Limited | Other services | 2026 |
| Archicasa Limited | Professional & scientific | 2014 |
| Archimydes PVT Ltd | Information & communication | 2023 |
| Archip Ltd | Professional & scientific | 2018 |
| Architectural Designs Services (UK) Ltd | Professional & scientific | 2017 |
| Archive Events Ltd | Professional & scientific | 2025 |
| Arco Recruitment Ltd | Administrative & support | 2009 |
| Arcs Properties Limited | Real estate | 2015 |
| Arctic Archipelago Ltd | Administrative & support | 2024 |
| Arcus Partners (AR) Limited | Financial services | 2022 |
| Arcus Partners (IM) Limited | Financial services | 2022 |
| Arcus Partners (MS) Limited | Financial services | 2022 |
| Arcus Partners Group Limited | Financial services | 2022 |
| Ardent People Limited | Professional & scientific | 2014 |
| Ardmore Resources Limited | Mining & quarrying | 1997 |
| Area Limited | Extraterritorial | 2000 |
| Arena Global Security Limited | Administrative & support | 2016 |
| Aresho Ltd | Health & social care | 2012 |
| Arete Bidco Limited | Financial services | 2025 |
| Arete Lifestyle Limited | Arts & recreation | 2018 |
| Arete Midco Limited | Financial services | 2025 |
| Arete Topco Limited | Financial services | 2025 |
| Argania Naturale Ltd | Extraterritorial | 2013 |
| Argyll Agencies Limited | Professional & scientific | 1972 |
| Aria Consulting Limited | Information & communication | 2014 |
| Aria Private Clients Limited | Financial services | 2009 |
| Aristar Financial Consulting Limited | Professional & scientific | 2010 |
| Aristar Training & Development Ltd | Education | 2016 |
| Ark-Light Limited | Real estate | 2021 |
| Arkipelago Ltd | Information & communication | 2026 |
| Arknu Foundations Limited | Real estate | 2023 |
| Arkus Construction Limited | Construction | 2022 |
| Armitage Accountants Limited | Professional & scientific | 2023 |
| Aroma Italy Limited | Hospitality | 2022 |
| Arpwright Consultancy Ltd | Professional & scientific | 2023 |
| Arra Management Ltd | Administrative & support | 2010 |
| Arridentia Solutions Limited | Construction | 2006 |
| Arsim UK Car Wash Limited | Administrative & support | 2014 |
| Art & Grind Ltd | Wholesale & retail | 2023 |
| Art Estates (Holdings) Limited | Financial services | 2023 |
| Art in Detail Limited | Professional & scientific | 2016 |
| Art in Kuzina Ltd | Hospitality | 2014 |
| Arthur Dog Ltd | Professional & scientific | 2014 |
| Artianne Limited | Other services | 2012 |
| Artifactually London Ltd | Wholesale & retail | 2012 |
| Artificial General Intelligence Limited | Administrative & support | 2018 |
| Artillery Road Management Company Limited | Real estate | 2009 |
| Artington Walk (Residents Association) Limited | Households | 1980 |
| Artists & Designers Associates Limited | Professional & scientific | 1999 |
| Artivion UK Ltd | Administrative & support | 1999 |
| Artventure Trust Limited | Administrative & support | 2005 |
| Artvogue Ltd | Wholesale & retail | 2014 |
| Artyfishal Intellygance Ltd | Professional & scientific | 2024 |
| Arundel Lodge Dental Surgery Ltd | Health & social care | 2011 |
| Arundell Consulting Ltd | Information & communication | 2026 |
| Arvate Limited | Information & communication | 2010 |
| AS Roofing Surrey Ltd | Construction | 2025 |
| Asamoo Health Limited | Health & social care | 2022 |
| Asas Acquisition Limited | Real estate | 2021 |
| ASB Group Services Limited | Professional & scientific | 2022 |
| Ascendant Capital Limited | Financial services | 2014 |
| Ascense Ltd | Wholesale & retail | 2022 |
| Ascii Consulting Limited | Information & communication | 2008 |
| Ascot Timber Buildings Limited | Manufacturing | 2002 |
| ASD Property Investments Limited | Real estate | 2017 |
| ASH Research Consultancy (ARC) Limited | Administrative & support | 2012 |
| ASH Road SS Limited | Other services | 2012 |
| ASH Telecommunications Limited | Information & communication | 1998 |
| Ashbourne Poole Ltd | Health & social care | 2014 |
| Ashby GAS Services Ltd. | Construction | 2012 |
| Ashdown House Management Company Limited | Households | 1988 |
| Ashen Ventures Limited | Financial services | 2019 |
| Ashgate Communications Limited | Professional & scientific | 2002 |
| Ashgrove Homes Eastern Limited | Construction | 2015 |
| Ashgrove Homes Limited | Construction | 2013 |
| Ashgrove Homes Property 1020P1 Limited | Real estate | 2020 |
| Ashgrove Homes Property 1020P2 Limited | Real estate | 2020 |
| Ashgrove Homes Property 1035 Limited | Real estate | 2018 |
| Ashgrove Homes Property Limited | Real estate | 2018 |
| Ashgrove Homes Southern Limited | Construction | 2014 |
| Ashgrove Homes Western Limited | Construction | 2014 |
| Ashira Limited | Hospitality | 2007 |