| Aquablugames Ltd | Arts & recreation | 2019 |
| Aquacadabra Ltd | Wholesale & retail | 2013 |
| Aquadrive Ltd | Transport & logistics | 2026 |
| Aquasol Engineering (UK) Co., Limited | Water & waste | 2021 |
| Aquaswim Ltd | Arts & recreation | 2016 |
| Aquavita Holdings Ltd | Financial services | 2026 |
| Aquila Jewellery Ltd | Wholesale & retail | 2021 |
| AR Designs Limited | Manufacturing | 2002 |
| AR Hive Ltd | Information & communication | 2023 |
| AR Pharma Group Limited | Wholesale & retail | 2023 |
| AR Properties (Brighton) Limited | Real estate | 2012 |
| Ara-Cure Ltd | Health & social care | 2012 |
| Arabel Lebrusan Limited | Wholesale & retail | 2015 |
| Aralewa Limited | Wholesale & retail | 2016 |
| Aram Yoga Limited | Education | 2020 |
| Aramis Computing Services Limited | Extraterritorial | 1984 |
| Aras an Teaghlaigh Limited | Real estate | 2025 |
| Aras Consulting Ltd | Other services | 2014 |
| Aravem Ltd | Financial services | 2022 |
| Arbortopia Ltd | Administrative & support | 2004 |
| Arbworx Limited | Other services | 2008 |
| ARC Educate Ltd | Information & communication | 2020 |
| ARC EN Ciel Software Limited | Information & communication | 2004 |
| ARC Event Management Sussex Limited | Arts & recreation | 2025 |
| ARC Intercapital Limited | Professional & scientific | 2000 |
| ARC Sussex Carpentry Ltd | Manufacturing | 2026 |
| ARC. Sphere Limited | Professional & scientific | 2016 |
| Arcadeextend Limited | Administrative & support | 2003 |
| Arcadia Cigars Bond Street Limited | Wholesale & retail | 2025 |
| Arcadia Cigars Church Street Limited | Wholesale & retail | 2025 |
| Arcadia Imaging Limited | Health & social care | 2023 |
| Arcadia Retail Limited | Wholesale & retail | 2025 |
| Arcadis International Limited | Professional & scientific | 1988 |
| Arcanic CIC | Administrative & support | 2022 |
| Arch Health Community Interest Company | Health & social care | 2016 |
| Arch Podiatry Ltd | Other services | 2020 |
| Arch-Angels Architects Limited | Professional & scientific | 2008 |
| Archangel Financial Services Ltd | Administrative & support | 2018 |
| Archer and Bowmans Limited | Construction | 2024 |
| Archer Publications Limited | Wholesale & retail | 1992 |
| Archers Field Estate Management Company Limited | Households | 2022 |
| Archimedes Solutions Limited | Information & communication | 2009 |
| Archion Limited | Professional & scientific | 2017 |
| Archipelagos Consulting Ltd | Professional & scientific | 2017 |
| Archon IT Ltd | Information & communication | 2018 |
| Archway Builders (Sussex) Ltd | Construction | 2016 |
| Arcr Holding Ltd | Financial services | 2026 |
| Arctos Works Ltd | Construction | 2016 |
| Arcus Vapour Ltd | Wholesale & retail | 2017 |
| Ardant Pharmaceuticals Ltd. | Wholesale & retail | 2014 |
| Ardent Property Limited | Construction | 2016 |
| Ardon Construction Limited | | 1965 |
| Ardra Ltd | Real estate | 2018 |
| Areli Care Ltd | Health & social care | 2017 |
| Aren Fish Bar Ltd | Hospitality | 2025 |
| Arequipa Reef Ltd | Households | 2005 |
| Arete Group Holdings Limited | Financial services | 2024 |
| Arete Market Research Limited | Professional & scientific | 2024 |
| Arete Medical Community Limited | Professional & scientific | 2024 |
| Arete Smart Homes Ltd | Construction | 2025 |
| Argyle Tyres & Auto Services Ltd | Wholesale & retail | 2022 |
| ARH Consultants (Sussex) Ltd | Administrative & support | 2025 |
| Aria Services Limited | Transport & logistics | 1999 |
| Ariani Ltd | Information & communication | 2005 |
| Arif Barbers Ltd | Other services | 2019 |
| Arisio Ltd | Information & communication | 2024 |
| Arisound Limited | Households | 1995 |
| ARJ Pubs Ltd | Hospitality | 2019 |
| ARK Urban Spaces Ltd | Construction | 2026 |
| Arka Limited | Wholesale & retail | 2009 |
| Arke Agency Ltd | Professional & scientific | 2017 |
| Arkwrights Limited | Wholesale & retail | 2002 |
| Arlea Studios Ltd | Information & communication | 2020 |
| Arlingsworth Solicitors Limited | Professional & scientific | 2012 |
| Arlington Mews Management Company Limited | Households | 2000 |
| Arlo Investments Ltd | Real estate | 2022 |
| Armetech Ltd | Wholesale & retail | 2021 |
| Arms Management Company Limited | Administrative & support | 2020 |
| Armstrong Cary LLP | | 2015 |
| Armstrong Teasdale Limited | Professional & scientific | 2014 |
| Armstrongs Property Services Ltd | Construction | 2001 |
| Armten Limited | Households | 1984 |
| ARN Dynamic Solutions Limited | Professional & scientific | 2021 |
| ARN Roofing Ltd | Construction | 2024 |
| Arnlan Properties Limited | Real estate | 2002 |
| Arnoldact Rose Limited | Financial services | 2003 |
| Aron Coates Architecture Limited | Professional & scientific | 2007 |
| Array LED Limited | Wholesale & retail | 2009 |
| Arro Talent Ltd | Professional & scientific | 2025 |
| Arrow Mortgage Solutions Ltd | Financial services | 2020 |
| Arsha Construction Ltd | Construction | 2021 |
| Arsr Limited | Real estate | 2015 |
| Art Animal Ltd | Professional & scientific | 2023 |
| Art Box Removals Limited | Transport & logistics | 2026 |
| Art Break Ltd | Arts & recreation | 2016 |
| Art Data Systems Limited | Information & communication | 1996 |
| Art for Peace Festival Ltd | Wholesale & retail | 2023 |
| Art HOC Community Interest Company | Arts & recreation | 2020 |
| Art of Buying Limited | Professional & scientific | 2018 |
| Art of Contemporary Yoga Limited | Education | 2008 |