| Aqua Artes Swim School Ltd | Education | 2020 |
| Aquacare Limited | Water & waste | 2003 |
| Aquaclean Property Ltd | Real estate | 2025 |
| Aquasolari Limited | Wholesale & retail | 2006 |
| Aquasphinx Limited | Professional & scientific | 2020 |
| AR Software Consulting Ltd | Information & communication | 2025 |
| Arabema Construction Support Ltd | Construction | 2025 |
| Arabic Doctors Ltd | Health & social care | 2023 |
| Arbor Cura Tree Surgery Limited | Agriculture & fishing | 2012 |
| Arbor Place Ltd | Real estate | 2018 |
| ARC Logistics Ltd | Transport & logistics | 2019 |
| ARC Shed Ltd | Professional & scientific | 2019 |
| Arch Industries (UK) Limited | Real estate | 2012 |
| Archer House Legal Services Limited | Professional & scientific | 2023 |
| Arctic Air Limited | Construction | 2004 |
| Arctium Ltd | Professional & scientific | 2011 |
| Arcus Partnership Limited | Professional & scientific | 2002 |
| Ardenya Ltd | Households | 1980 |
| Ardingly College International Limited | Administrative & support | 2018 |
| Ardingly College Limited | Education | 1999 |
| Ardingly Projects Limited | Hospitality | 1985 |
| Ardingly Rowing Club Ltd | Arts & recreation | 2014 |
| Ardingly Village Club | Arts & recreation | 2008 |
| Ardisson Associates 1805 Ltd | Professional & scientific | 2022 |
| ARE WE Wayward Investments Limited | Professional & scientific | 2022 |
| Area City Limited | Other services | 2018 |
| ARG Solutions Ltd | Manufacturing | 2025 |
| Ariya Holdings Limited | Real estate | 2019 |
| ARK Games Limited | Professional & scientific | 2017 |
| Arka Original Funerals Limited | Other services | 2003 |
| Arksen & 10% for the Ocean Ltd | Information & communication | 2019 |
| Arksen Adventures Limited | Administrative & support | 2021 |
| Arksen Limited | Manufacturing | 2017 |
| Armahill Limited | Administrative & support | 2000 |
| Armoire Group (AG) Ltd | Construction | 2025 |
| Armstrong Bodyshop Limited | Wholesale & retail | 2004 |
| Armstrong Starbuck Consulting Ltd | Professional & scientific | 2026 |
| Arprop Estates Limited | Real estate | 2017 |
| Art by Nature Ltd | Wholesale & retail | 2025 |
| Artcuts Limited | Manufacturing | 2012 |
| Artek Build Limited | Construction | 2014 |
| Artemis Research Associates Limited | Other services | 2012 |
| Arthur Barber Ltd | Manufacturing | 2025 |
| Artisan Studio Tailoring Ltd | Manufacturing | 2026 |
| Artist DOT Partners UK Ltd | Professional & scientific | 2025 |
| Artistra Renovations Limited | Construction | 2015 |
| Artologie Limited | Wholesale & retail | 2014 |
| Arts and Creatives Designs Ltd | Professional & scientific | 2016 |
| Artt Developments Limited | Financial services | 2025 |
| Arun 2022 Company | Financial services | 2023 |
| Arun Mowers Limited | Other services | 2003 |
| Arzak Management Consultancy Limited | Administrative & support | 2008 |
| ASH Events, Marketing & Fundraising Limited | Professional & scientific | 2026 |
| ASH International Limited | Extraterritorial | 2016 |
| Ashdown and General Land Company (the) | Agriculture & fishing | 1981 |
| Ashdown Forest Consultancy Limited | Administrative & support | 2009 |
| Ashdown Riding Ltd | Education | 2020 |
| Ashdown Roofing Supplies Limited | Wholesale & retail | 2002 |
| Ashdown Scaffolding Ltd | Construction | 2020 |
| Ashenground Community Centre | Health & social care | 2002 |
| Ashley Freeman & Company Limited | Professional & scientific | 2016 |
| Ashmoor Engineering and Property Services Ltd | Professional & scientific | 2011 |
| Ashpole Aviation Services Limited | Professional & scientific | 2018 |
| Ashton Healthcare Group Ltd | Administrative & support | 2007 |
| Ashton Project Management Limited | Administrative & support | 2019 |
| Ashurst Place Residents Management Company Limited | Households | 2001 |
| Ashwood Contracting (Services) Limited | Administrative & support | 2012 |
| Ashé School of Dance Limited | Arts & recreation | 2026 |
| Asia Broadcast Service Limited | Information & communication | 2023 |
| ASK US Homes Ltd | Other services | 2019 |
| Askalane Services Limited | Professional & scientific | 2018 |
| Aspect Gardens Limited | Administrative & support | 2007 |
| Aspen International Limited | Professional & scientific | 1986 |
| Aspen Management Consulting Limited | Administrative & support | 2025 |
| Aspire People Development Ltd | Professional & scientific | 2014 |
| Assay Earth Ltd | Professional & scientific | 2026 |
| Asset + Legal Services Limited | Professional & scientific | 2020 |
| Asset Alternatives Limited | Financial services | 2016 |
| Asset Plus Financial Limited | Administrative & support | 2006 |
| Associate Planet Limited | Information & communication | 2011 |
| Astara Omega Limited | Professional & scientific | 2025 |
| Asterisk Limited | Real estate | 1980 |
| Asterisk Special Projects Limited | Real estate | 2019 |
| Astral Systems Ltd | Administrative & support | 2010 |
| AT Foxwarren Consulting Limited | Professional & scientific | 2024 |
| Ateea Limited | Wholesale & retail | 2022 |
| Atelier Points Ltd. | Arts & recreation | 2004 |
| Atelier T&B Limited | Professional & scientific | 2021 |
| Atkinsons Plumbing & Heating Limited | Construction | 2019 |
| Atlas 681 Ltd | Transport & logistics | 2026 |
| Atlas Empire Limited | Administrative & support | 2022 |
| Atlas Mobility (Sussex) Ltd | Wholesale & retail | 2016 |
| Atlas Mobility Limited | Real estate | 2017 |
| Atlas Roofcare Limited | Professional & scientific | 2026 |
| Atomic Rambo Coaching Ltd | Education | 2025 |
| Atomik Group Limited | Wholesale & retail | 2025 |
| Atradia Limited | Professional & scientific | 2001 |
| ATZ Assets Ltd | Real estate | 2026 |
| Audessence Limited | Manufacturing | 2005 |
| Audioworks Limited | Professional & scientific | 2011 |