| Alpha House Annandale Limited | Households | 2020 |
| Alpha Point IT Ltd | Information & communication | 2022 |
| Alphabet & Sign City Limited | Manufacturing | 2009 |
| Alphie Ltd | Health & social care | 2026 |
| Alpia Consulting Limited | Information & communication | 2023 |
| ALR Caterers Limited | Hospitality | 1977 |
| Alro Properties Limited | Administrative & support | 1988 |
| Alteg UK Ltd | Wholesale & retail | 2025 |
| ALVYDAS1990 Ltd | Transport & logistics | 2020 |
| Amalfi Consultancy Ltd | Information & communication | 2022 |
| Ambridge Court Management Limited | Households | 1990 |
| Ampco Limited | Professional & scientific | 2007 |
| Amphion Ltd | Wholesale & retail | 2012 |
| Amrose Design Services Limited | Professional & scientific | 2018 |
| Amsg Limited | Real estate | 2020 |
| AN Construction Specialists Limited | Construction | 2014 |
| Anassa Group Ltd | Administrative & support | 2023 |
| Anchor Point Rope Access Ltd | Other services | 2022 |
| Anclamar Ltd | Administrative & support | 2018 |
| Andersen VA Ltd | Extraterritorial | 2019 |
| Anderson Whyte Associates Ltd | Construction | 2021 |
| Andrew Fells Consulting Ltd. | Professional & scientific | 2017 |
| Andrew John Gibbs Limited | Extraterritorial | 2024 |
| Anglo Encounter Limited | Other services | 1995 |
| Anglo Plumbing, Heating & GAS Engineers Ltd | Construction | 2017 |
| Animal Volunteers Africa Ltd | Administrative & support | 2025 |
| Anna Emilia Design Limited | Professional & scientific | 2017 |
| Anna Krason Beauty Ltd | Other services | 2022 |
| Annie Bundfuss Limited | Professional & scientific | 2014 |
| Anra Group Ltd | Financial services | 2018 |
| Anthony Billings Consulting Limited | Education | 2022 |
| Ants Barbershop & Co Ltd | Other services | 2019 |
| Anuradha Enterprises Limited | Hospitality | 2013 |
| ANY Automotive Limited | Wholesale & retail | 2020 |
| Apale Locum Ltd | Wholesale & retail | 2022 |
| Apex Technical Solutions Ltd | Construction | 2024 |
| APJ Builders Limited | Construction | 2016 |
| APL Film Cars Ltd | Information & communication | 2014 |
| Apletree Accountancy Services Ltd | Professional & scientific | 2018 |
| APN Home Services Ltd | Manufacturing | 2014 |
| Apollo Eagle Consulting Limited | Professional & scientific | 2020 |
| Appas Events Limited | Arts & recreation | 2022 |
| Appliance Cover Assured Ltd | Other services | 2020 |
| Appliance Group Limited | Other services | 2016 |
| Appylab Ltd | Information & communication | 2013 |
| Aquatec Heating and Plumbing Limited | Construction | 2007 |
| Aqueous Carpet and Upholstery Cleaning Limited | Other services | 2016 |
| Arad SA Ltd | Real estate | 2026 |
| ARC Power Engineering Ltd | Administrative & support | 2025 |
| Arch House Management Company Limited | Households | 1979 |
| Archemys Partnerships Limited | Professional & scientific | 2023 |
| Architectura Design Limited | Extraterritorial | 2006 |
| Architectural Facade Solutions Limited | Construction | 2003 |
| Area Refrigeration Services Limited | Manufacturing | 2015 |
| Arezbu Ltd | Other services | 2025 |
| Aries 2 Charters Ltd | Transport & logistics | 2022 |
| Arkview Ltd | Construction | 2024 |
| Armourlight Limited | Manufacturing | 2015 |
| Aromaglo Limited | Other services | 2020 |
| Arrolbeam Management Company Limited | Households | 2014 |
| Arrvis Homes Ltd | Real estate | 2022 |
| Art Dyno & Suspension Ltd | Wholesale & retail | 2023 |
| Art Printers Ltd | Manufacturing | 2008 |
| Art Surrey Limited | Arts & recreation | 2023 |
| Arthur E. Edwards Ltd | Construction | 2024 |
| Arthur Hayes Crowborough Ltd | Wholesale & retail | 2020 |
| Arthur Hayes Ltd | Wholesale & retail | 2018 |
| Artima Limited | Transport & logistics | 2020 |
| Artisanda Limited | Administrative & support | 2002 |
| Artwork Portal Limited | Other services | 2020 |
| Arun and Chichester Citizens Advice Bureau | Information & communication | 2003 |
| Arun Arts Company Limited | Arts & recreation | 1996 |
| Arun Business Park Limited | Real estate | 1984 |
| Arun Business Partnership CIC | Administrative & support | 2016 |
| Arun Business Solutions Limited | Administrative & support | 2020 |
| Arun Chase (NO.1) Management Company Limited | Real estate | 1991 |
| Arun Instruments Ltd | Wholesale & retail | 2004 |
| Arun Meat & Livestock Company Limited | Agriculture & fishing | 1982 |
| Arun Place Management Company Limited | Households | 2015 |
| Arundel Accommodation Limited | Hospitality | 2024 |
| AS Escarda Limited | Other services | 2014 |
| Ashcroft Restoration Clean Limited | Construction | 2022 |
| Ashfast Limited | Wholesale & retail | 2020 |
| Ashley Coupe Limited | Real estate | 2018 |
| Ashton Care (Bognor Regis) Limited | Health & social care | 2018 |
| ASJ Electrical Sussex Ltd | Construction | 2024 |
| Aspenstar Accommodation Ltd | Real estate | 2018 |
| Aspenstar Property Investments Ltd | Real estate | 2018 |
| Aspired Scaffolding UK Limited | Construction | 2011 |
| Asset Homes Private Ltd | Real estate | 2022 |
| Asset Management Advisors Limited | Information & communication | 2014 |
| Asterisk Investments Ltd | Professional & scientific | 2026 |
| Asteron Applied Sciences Ltd | Hospitality | 2026 |
| Astita Ltd | Real estate | 2024 |
| Aston Court Management Limited | Households | 2001 |
| Astonish Cleaning Services Limited | Administrative & support | 2021 |
| Astonish Commercial Cleaning Services Limited | Administrative & support | 2022 |
| ATC Structural Engineers Ltd | Professional & scientific | 2020 |
| Atheleticsportsuk Ltd | Wholesale & retail | 2025 |
| Athrington Court Residents Association Limited | Households | 1984 |