| Art of Music Ltd | Information & communication | 2020 |
| Art Rugs Ltd | Manufacturing | 2007 |
| Artemis Aerospace Holdings Limited | Financial services | 2024 |
| Arthaus Limited | Wholesale & retail | 2004 |
| Artillium Finance Limited | Professional & scientific | 2023 |
| Artillium Real Estate Finance Limited | Professional & scientific | 2024 |
| Artis Skin Care Ltd | Health & social care | 2020 |
| Artist Anon Limited | Wholesale & retail | 2011 |
| Artist License Ltd | Information & communication | 2023 |
| Artnetik Ltd | Wholesale & retail | 2025 |
| Arundel Villas Residents Association Limited | Households | 1986 |
| Arya Cyber Security Solutions Ltd | Information & communication | 2025 |
| Arête One Limited | Manufacturing | 2018 |
| AS Business Management Ltd | Professional & scientific | 2019 |
| AS DE Espadas Ltd | Hospitality | 2025 |
| AS Intended Brewing Ltd | Manufacturing | 2025 |
| AS Intended Ltd | Manufacturing | 2025 |
| AS Recruitment Services UK Limited | Administrative & support | 2013 |
| AS Services a UK Ltd | Administrative & support | 2019 |
| Asaiya Ltd | Health & social care | 2024 |
| Asake Enterprises Limited | Administrative & support | 2024 |
| ASB Dental Limited | Health & social care | 2023 |
| Asbo Ltd | Manufacturing | 2024 |
| Ascend Study Ltd | Education | 2026 |
| Ascent Coaching Company Limited | Professional & scientific | 2006 |
| Ascent Housing Solutions Ltd | Real estate | 2022 |
| Ascii Limited | Financial services | 2017 |
| Aseell Ltd | Construction | 2020 |
| ASH Properties (2018) Ltd | Real estate | 2018 |
| Ashar Limited | Arts & recreation | 2013 |
| Ashbaccara Ltd | Hospitality | 2021 |
| Ashbourne Asset Management Ltd | Extraterritorial | 2015 |
| Ashby Solar Farm Limited | Energy | 2015 |
| Ashchurch Homestead Limited | Real estate | 2020 |
| Ashdown (Eaton Road) (Hove) Managements Limited | Households | 1973 |
| Ashley Court (Hove) Limited | Households | 1996 |
| Ashman Properties Limited | Real estate | 2006 |
| Ashworks Limited | Construction | 2012 |
| Asia UK Travelling Ltd | Administrative & support | 2018 |
| Asiana Brighton Ltd | Wholesale & retail | 2018 |
| Asiana Global Group UK - Tailor-Made Yacht Charters International Limited | Other services | 2011 |
| Asim Auto Ltd | Wholesale & retail | 2023 |
| ASK a Pilot Ltd | Transport & logistics | 2020 |
| Askell Ltd | Professional & scientific | 2012 |
| Asot Consulting Limited | Administrative & support | 2022 |
| Aspen Place Ltd | Health & social care | 2007 |
| Aspire Homes (Southern) Ltd | Construction | 2019 |
| Aspire Safeguarding Ltd | Health & social care | 2024 |
| Asset Lifecycle Management Limited | Extraterritorial | 2022 |
| Associated Skilled Professionals Limited | | 1987 |
| Association of Clinical Pathologists(The) | Other services | 1956 |
| Assure Protections Ltd | Other services | 2020 |
| Aswang Ltd | Hospitality | 2026 |
| Atariya Cafe Japan Limited | Hospitality | 2020 |
| Atariya Foods Limited | Wholesale & retail | 2016 |
| Atariya-Ishimitsu UK Ltd | Financial services | 2023 |
| ATB4 Ltd | Professional & scientific | 2023 |
| ATC Partnership Ltd | Professional & scientific | 2012 |
| ATD Consulting Limited | Administrative & support | 2024 |
| ATH Kingdom Ltd | Wholesale & retail | 2022 |
| Athenas Crystals Limited | Wholesale & retail | 2021 |
| Atheralls Farms Limited | Agriculture & fishing | 1984 |
| Athlon Property Ltd | Real estate | 2024 |
| Atif Warraich Limited | Public administration | 2017 |
| Atkinsons Accountants Limited | Professional & scientific | 2013 |
| Atlantic Archives Limited | Administrative & support | 2025 |
| Atlantici Ltd | Information & communication | 2025 |
| Atlas English Ltd | Education | 2019 |
| Atlingcourt Properties Limited | Households | 1994 |
| Atlingworth Mansions Limited | Households | 1996 |
| Atmanitrades Ltd | Professional & scientific | 2026 |
| Atomic Entertainment Limited | Arts & recreation | 2019 |
| Attossi Interprise Ltd | Health & social care | 2018 |
| Attree Court Freeholders Limited | Real estate | 2000 |
| ATW Renovations Ltd | Construction | 2019 |
| Auction Rooms (Brighton) Management Limited | Extraterritorial | 2013 |
| Audax UK Limited | Administrative & support | 2003 |
| Audeo Accounting Ltd | Professional & scientific | 2012 |
| Audio 7 Limited | Wholesale & retail | 2003 |
| Audiographica Media Ltd | Wholesale & retail | 2021 |
| Aulakh Traders Limited | Wholesale & retail | 2025 |
| Aura Agency Limited | Wholesale & retail | 2014 |
| Aurax Media Limited | Professional & scientific | 2024 |
| Aurelian Clinical Services Limited | Health & social care | 2026 |
| Aurelian Ventures Ltd | Professional & scientific | 2023 |
| Auric Capital Ltd | Financial services | 2015 |
| Aurora Lights Limited | Construction | 2010 |
| Aurum Hove Limited | Households | 2020 |
| Authentic Resilience Ltd | Professional & scientific | 2022 |
| Autism Early Start Ltd | Education | 2023 |
| Auto Moda Limited | Wholesale & retail | 2016 |
| Auto Top Service Ltd | Wholesale & retail | 2021 |
| Autocare (Hove) Limited | Wholesale & retail | 2003 |
| Autolox Ltd | Wholesale & retail | 2020 |
| Automatic Gearbox Centre Limited | Wholesale & retail | 1985 |
| Autonomous Media Ltd | Professional & scientific | 2021 |
| Autopaints (South East) Limited | Wholesale & retail | 2018 |
| Autumn Lodge Hove Limited | Health & social care | 2018 |
| Auxo Consultancy Limited | Administrative & support | 2023 |
| AV Energy Limited | Professional & scientific | 2015 |