| Arcoco Ltd | Wholesale & retail | 2017 |
| Ardent Partner Limited | Professional & scientific | 2025 |
| Ardmore House Hotel Limited | Hospitality | 2000 |
| ARE (Moss END) Limited | Real estate | 2015 |
| Arena Advisory Group Limited | Information & communication | 2025 |
| Arena Hydra Ltd | Information & communication | 2026 |
| Argebe Ltd | Wholesale & retail | 2026 |
| Argent Star Ltd | Professional & scientific | 2025 |
| Argo Vehicles Limited | Wholesale & retail | 1999 |
| Argyll Energy Services Limited | Professional & scientific | 2015 |
| Ariel & Bell Pictures Ltd | Information & communication | 2017 |
| Arif's Cafe Limited | Hospitality | 2023 |
| Arin Properties Ltd | Real estate | 2025 |
| Aristos Financial Management Limited | Professional & scientific | 2014 |
| ARJ Construction Holdings Limited | Financial services | 2013 |
| ARJ Construction Limited | Construction | 2005 |
| ARJ Construction Property Limited | Real estate | 2013 |
| Arkley Fine Art Limited | Wholesale & retail | 2017 |
| Arkley Property Management Ltd | Construction | 2025 |
| Armco Solutions Ltd | Professional & scientific | 2014 |
| Arms-Tec Ltd | Wholesale & retail | 2025 |
| Armstridge Residents Association Ltd | Households | 2020 |
| ARN Trading Ltd | Wholesale & retail | 2009 |
| Arnold James (ST. Albans) Limited | Construction | 1958 |
| Aroma Curry Ltd | Hospitality | 2026 |
| Aroma Express Ltd | Real estate | 2014 |
| ARP Transport Limited | Transport & logistics | 2014 |
| Arrival IT Ltd | Information & communication | 2011 |
| Arroyo-Rocha Design Ltd | Information & communication | 2020 |
| Art Inspiration Ltd | Extraterritorial | 2020 |
| Art Technologies Limited | Information & communication | 2020 |
| Art USE Ltd | Information & communication | 2019 |
| ART2LEARN Ltd | Wholesale & retail | 2025 |
| Artakian Ltd | Real estate | 2020 |
| Artan (UK) Limited | Construction | 2012 |
| Artemis Enterprise Ltd | Professional & scientific | 2009 |
| Artis Homes Ltd | Construction | 2021 |
| Artist Charter Services Ltd | Transport & logistics | 2019 |
| Artizan (London) Ltd | Administrative & support | 2025 |
| Artoplasia Ltd | Hospitality | 2022 |
| Artos Limited | Other services | 2017 |
| Artseen CIC | Arts & recreation | 2025 |
| Artsense Games Ltd | Information & communication | 2020 |
| Artspool Education Ltd | Education | 2020 |
| Aruks Ltd | Wholesale & retail | 2018 |
| ASA Developments Group Ltd | Real estate | 2024 |
| ASA Music Limited | Arts & recreation | 2019 |
| Asap Consulting Limited | Professional & scientific | 2005 |
| Asap Solutions Limited | Transport & logistics | 2015 |
| Ascend Holding I SPV LLP | | 2022 |
| Ascendx Angel SPV LLP | | 2023 |
| Ascendx SPV LLP | | 2023 |
| Ascj Distributions Ltd | Transport & logistics | 2025 |
| Aseci Ltd | Information & communication | 2025 |
| ASH Certified Construction Services Limited | Administrative & support | 2017 |
| Ashbridge TW Engineering Ltd | Professional & scientific | 2024 |
| Ashbury House Limited | Other services | 2018 |
| Ashby Design Limited | Administrative & support | 2002 |
| Ashford & Vale Estates Ltd | Real estate | 2005 |
| Ashford Procurement UK Ltd | Hospitality | 2013 |
| Ashford Town Football Club Limited | Arts & recreation | 2000 |
| Ashman Finance Limited | Financial services | 2017 |
| Ashmic Consulting Ltd | Professional & scientific | 2015 |
| Ashmore Financial Limited | Professional & scientific | 2015 |
| Ashridge Technologies Limited | Information & communication | 1995 |
| Ashwood Mews Management Company Limited | Hospitality | 2000 |
| Asieltec Limited | Information & communication | 2008 |
| Aslan UK Consulting Limited | Professional & scientific | 2016 |
| Asna Investments Ltd | Households | 2026 |
| Asnu Special Projects Limited | Administrative & support | 2025 |
| Aspa Property Services Limited | Real estate | 2018 |
| Aspar Pharmaceuticals Limited | Manufacturing | 1991 |
| Asparagus Consulting Limited | Professional & scientific | 2013 |
| Aspen Close Management Company (Bricket Wood) Limited | Households | 1992 |
| Aspin Financial Limited | Financial services | 2015 |
| Asport Ltd | Wholesale & retail | 2024 |
| Assaf Frank Ltd | Arts & recreation | 2002 |
| Assessment Central Limited | Administrative & support | 2010 |
| Asset Investments & Holdings Ltd | Construction | 2020 |
| Assetwatch MCC SPV1 LLP | | 2023 |
| Associates Roofing Partnership Ltd | Construction | 2022 |
| Association of Spanish Nurses and Healthcare Workers Isabel Zendal | Other services | 2025 |
| Assuche Ltd | Professional & scientific | 2013 |
| Aster House Ltd | Hospitality | 2026 |
| Astil Limited | Information & communication | 2024 |
| Aston Caterers Limited | Hospitality | 1977 |
| Aston Flooring Limited | Construction | 2007 |
| Astoria Bids & Tenders Ltd | Administrative & support | 2020 |
| Astralis Foundation | Education | 2024 |
| Astrasana UK Limited | Professional & scientific | 2023 |
| Astrix Health Limited | Information & communication | 2024 |
| Astute Headhunting Ltd | Administrative & support | 2022 |
| Asymptotic Holdings Limited | Information & communication | 2026 |
| AT the Counter Ltd | Manufacturing | 2023 |
| ATD Partners Limited | Professional & scientific | 2011 |
| Atelier Ferrari & Monti Limited | Information & communication | 2013 |
| Atharv Homes Ltd | Real estate | 2023 |
| Atharv Ltd. | Health & social care | 2016 |
| Atheena Prime Logistics Ltd | Transport & logistics | 2026 |
| Athena BDA Ltd | Information & communication | 2024 |