| 1929 Technique Limited | Manufacturing | 2025 |
| 1ST 4COACHES Ltd | Transport & logistics | 2008 |
| 23 Eastcourt RD Ltd | Real estate | 2024 |
| 24 Old Shoreham Road (Freehold) Limited | Real estate | 2014 |
| 264 Northborough Road Freehold Limited | Real estate | 2024 |
| 3D and 6D Pictures Ltd | Information & communication | 2009 |
| 3D Concrete Limited | Construction | 2013 |
| 3TIS Estate Ltd | Real estate | 2023 |
| 44 Old Shoreham Road (Brighton) Limited | Hospitality | 2005 |
| 4G Kitchens Ltd | Manufacturing | 2018 |
| 5 to 6 Orchard Gardens Freehold Limited | Households | 2025 |
| 51 Millers Road (Brighton) Limited | Households | 2015 |
| 52 Grafton Road Worthing (RTM) Ltd | Real estate | 2010 |
| 54 Marville Road Ltd | Hospitality | 2016 |
| 93 Station Road Ltd | Real estate | 2016 |
| 98 NOT OUT Limited | Administrative & support | 2018 |
| A B Shipping Limited | Extraterritorial | 1998 |
| A J Frost Ltd | Wholesale & retail | 2003 |
| A&E Dental Engineering Ltd | Professional & scientific | 2017 |
| A.H.Bowerman and SON Limited | Professional & scientific | 1959 |
| A.L.P Creative Ltd | Manufacturing | 2012 |
| A.L.P Management Solutions Ltd | Manufacturing | 2012 |
| AA Publishing Limited | Information & communication | 2011 |
| AA Tech and Property Ltd. | Real estate | 2022 |
| Abbott Walsingham Limited | Real estate | 2017 |
| ABO Limited | Information & communication | 1992 |
| AC Joinery & Carpentry Ltd | Manufacturing | 2026 |
| Ace Displays Limited | Manufacturing | 2006 |
| Acorn Cattery West Sussex Limited | Other services | 2018 |
| Acorn Technical Associates Ltd | Professional & scientific | 2014 |
| Activity Publishing Limited | Information & communication | 2025 |
| ADA Expedite Ltd | Transport & logistics | 2025 |
| Adept Heating & Mechanical Services Limited | Other services | 2002 |
| ADM Accounting Ltd | Administrative & support | 2017 |
| Adsl Limited | Health & social care | 2021 |
| AEF Window Cleaning Limited | Administrative & support | 2024 |
| Aegcbs Ltd | Wholesale & retail | 2024 |
| Aeroroom Limited | Manufacturing | 2014 |
| Aewc Limited | Professional & scientific | 2008 |
| AFD Transport Limited | Transport & logistics | 2003 |
| Agrirevive Parts & Service Limited | Wholesale & retail | 2025 |
| Airbase Ltd | Information & communication | 2018 |
| Airwork (Pneumatics) Limited | Wholesale & retail | 2005 |
| AJ Services Brickcutters Ltd | Manufacturing | 2011 |
| Akfp Consulting Ltd | Professional & scientific | 2026 |
| Alchemy Contracting Ltd | Construction | 2021 |
| Alcodigital Limited | Wholesale & retail | 2000 |
| Aleworks Brewing Company Ltd | Manufacturing | 2021 |
| Alex Newson Tree Services Ltd | Agriculture & fishing | 2025 |
| Alexandra Bastedo (Champions) Animal Sanctuary Limited | Arts & recreation | 2009 |
| Alicia Development Ltd | Real estate | 2024 |
| ALL Hours Property Services Limited | Households | 2025 |
| ALL World ATV Parts Limited | Wholesale & retail | 2020 |
| Allen Studios Ltd | Professional & scientific | 2024 |
| Allied Estates (South East) Limited | Real estate | 1997 |
| Alma Proust Limited | Wholesale & retail | 2024 |
| ALP Trustees Limited | Professional & scientific | 2022 |
| Alsbury Group Ltd | Administrative & support | 2014 |
| Altitude Corporate Training Ltd | Transport & logistics | 2021 |
| Alun Smith Ltd | Financial services | 2025 |
| Alvaro Back VET Limited | Professional & scientific | 2019 |
| Amanda Patton Landscape & Garden Design Ltd | Administrative & support | 2015 |
| Amazing Lettings Ltd | Hospitality | 2025 |
| Amber Facilities Solutions Limited | Professional & scientific | 2014 |
| Amenity Water Management Limited | Construction | 2003 |
| Amorini Components Limited | Wholesale & retail | 1998 |
| Anatomically Correct Ltd | Information & communication | 2017 |
| Andrew JS Mussett Limited | Health & social care | 2009 |
| Andy-The-Vet Ltd | Professional & scientific | 2023 |
| Anesu-Mafadzo Ltd | Health & social care | 2017 |
| Anglo Dutch Consulting Limited | Professional & scientific | 2017 |
| Anstee Development LLP | | 2013 |
| Anthracites Properties Limited | Financial services | 2024 |
| Antiquum Ltd | Wholesale & retail | 2020 |
| Anya Brakha Ltd | Professional & scientific | 2021 |
| Aperture Supply Ltd | Wholesale & retail | 2026 |
| Apollo Garden Maintenance Limited | Administrative & support | 2018 |
| Aquadom Limited | Real estate | 1960 |
| Aran Gastronomy Limited | Hospitality | 2026 |
| Arcalian Limited | Wholesale & retail | 2002 |
| Archiflow Ltd | Information & communication | 2025 |
| Archisteel Ltd | Professional & scientific | 2025 |
| Architectural Plants (Brinsbury) Limited | Professional & scientific | 2014 |
| Architectural Plants 2020 Limited | Agriculture & fishing | 2020 |
| Architekton Architects Limited | Professional & scientific | 2025 |
| Arctic Cool Limited | Construction | 2023 |
| Arcus Aviation Consulting Limited | Professional & scientific | 2023 |
| Arden Resources Limited | Financial services | 2013 |
| Arih Developments Ltd | Real estate | 2025 |
| ARK Venture Investments Limited | Financial services | 2023 |
| Arlb Ventures Limited | Professional & scientific | 2018 |
| Arris Properties Limited | Real estate | 1921 |
| Artisan Recruitment (UK) Ltd | Administrative & support | 2014 |
| Arun Business Consulting Ltd | Professional & scientific | 2012 |
| Arun Classics Ltd | Wholesale & retail | 2013 |
| Arun Paving & Landscaping Limited | Construction | 2021 |
| Arun Prestige Limited | Wholesale & retail | 2019 |
| Arun Valley Consultancy Ltd | Professional & scientific | 2024 |
| Arundale Residents Management Company Limited | Households | 2012 |
| ARW Builders Ltd | Construction | 2011 |