| AGE Concern East Sussex | Health & social care | 2010 |
| AGE UK East Sussex Trading Limited | Financial services | 1998 |
| Aghr Management Services Limited | Professional & scientific | 1998 |
| Agiletechnik Limited | Professional & scientific | 2022 |
| Agjc Construction Limited | Construction | 2016 |
| Agricultura Ltd | Agriculture & fishing | 2026 |
| Agrishoots UK Limited | Wholesale & retail | 2021 |
| Aiden's Garden Services Ltd | Administrative & support | 2022 |
| Aidua Ltd | Health & social care | 2026 |
| Air Revolution Ltd | Energy | 2026 |
| Airworks Training Limited | Arts & recreation | 2011 |
| AJM Communications Ltd | Information & communication | 2022 |
| Ajrc Models Ltd | Wholesale & retail | 2025 |
| AK Nexus Learning Solutions Ltd | Education | 2025 |
| Akram Khan Productions Ltd | Arts & recreation | 2015 |
| Al-Singary Medical Limited | Health & social care | 2009 |
| Alan Stevenson Associates Limited | Professional & scientific | 2002 |
| Albion Economics Ltd | Professional & scientific | 2011 |
| Albion Languages Ltd | Information & communication | 2018 |
| Alburnum Ltd | Professional & scientific | 2018 |
| Aldrich Fundraising Limited | Professional & scientific | 2014 |
| Alex Jones Ltd | Health & social care | 2015 |
| Alexander DE Goldbregge (Estates) Ltd | Real estate | 2013 |
| Alexander Levy Company Limited | Real estate | 1947 |
| Alford Commercial Management Limited | Professional & scientific | 2025 |
| Alistair Boyd Limited | Wholesale & retail | 2002 |
| ALL Management Limited | Professional & scientific | 1995 |
| ALL Pallets Limited | Manufacturing | 1993 |
| ALL Things OIL Sussex Limited | Wholesale & retail | 2025 |
| Allan Gasson Limited | Professional & scientific | 2016 |
| Allectra Limited | Manufacturing | 2003 |
| Allingham Ltd | Arts & recreation | 2014 |
| Allington Place Management Company Limited | Households | 2006 |
| Allington Trust | Other services | 2016 |
| Allis Investments Limited | Information & communication | 2021 |
| Alta Executive Solutions Ltd | Information & communication | 2020 |
| Alternative Progression Limited | Administrative & support | 2010 |
| Alterv Health Ltd | Wholesale & retail | 2025 |
| Altogether Elsewhere Ltd | Real estate | 2022 |
| Altra Events Limited | Administrative & support | 2017 |
| Altus Accountancy & Tax Limited | Professional & scientific | 2016 |
| Altus Sports Management Ltd | Arts & recreation | 2015 |
| Alxad Properties Limited | Real estate | 2025 |
| AM 2 PM Catering Engineers Ltd. | Manufacturing | 2013 |
| Amanda's Cook School Limited | Hospitality | 2017 |
| Amandas Cook School Enterprise CIC | Hospitality | 2018 |
| Amber House Limited | Wholesale & retail | 2004 |
| Amicus Associates Ltd | Professional & scientific | 2002 |
| Amir 103 Real Estate Ltd | Households | 2012 |
| Ampedus Arboricultural Consultancy Limited | Professional & scientific | 2024 |
| AMS Property Services Sussex Ltd | Construction | 2023 |
| Amy's Cookery School Limited | Education | 2024 |
| Amygdala Solutions Ltd | Professional & scientific | 2020 |
| Anahata Integrated Health Clinic Limited | Health & social care | 2006 |
| Andrew Denning Imaging Referrals Ltd | Professional & scientific | 2016 |
| Andrews Healthcare Ltd | Wholesale & retail | 2004 |
| Animated Healthcare Ltd | Professional & scientific | 1997 |
| Animos Limited Liability Partnership | | 2003 |
| Anna Hayman Designs Limited | Professional & scientific | 2023 |
| Anna Standish Interiors Ltd | Professional & scientific | 2016 |
| Anne Fitzgerald Property Ltd | Real estate | 2021 |
| Anni Townend Limited | Administrative & support | 2013 |
| Annie Ralph Associates Ltd | Professional & scientific | 2006 |
| Anousha Ltd | Professional & scientific | 2022 |
| Anthony Pearce Ltd | Professional & scientific | 2024 |
| Antique Church Furnishings Limited | Wholesale & retail | 2002 |
| APM (Leasehold) Limited | Households | 2011 |
| APM Studios Ltd | Professional & scientific | 2003 |
| Appin Publishing Services Limited | Information & communication | 2003 |
| Aprima Ltd. | Households | 2008 |
| Aquaflame Sussex Ltd | Construction | 2022 |
| Aquamarine Surveys Ltd | Transport & logistics | 2025 |
| Aquamassage Ltd | Wholesale & retail | 2013 |
| ARB Automotive Group Ltd | Financial services | 2024 |
| Archidoc Ltd | Professional & scientific | 2019 |
| Archieshair Ltd | Other services | 2025 |
| Arden Executive Search Ltd | Administrative & support | 2026 |
| Arden Green Estate Management Ltd | Agriculture & fishing | 2026 |
| Area 16 Holdings Limited | Administrative & support | 2013 |
| Arietti People Development Ltd | Administrative & support | 2016 |
| Armon Restorations Ltd | Construction | 2026 |
| Armstrong Hunt Limited | Professional & scientific | 2006 |
| Art Crew Services Ltd | Professional & scientific | 2009 |
| Art Resource Limited | Other services | 1990 |
| Art UK Holdings Ltd | Financial services | 2024 |
| Article Design Studio Limited | Construction | 2015 |
| Arts for Healing CIC | Arts & recreation | 2025 |
| Arts Forward Community Interest Company | Other services | 2023 |
| Arts Media Contacts Ltd. | Information & communication | 2016 |
| Asap Driver Cover Ltd | Transport & logistics | 2012 |
| Asap Group Holdings Ltd | Transport & logistics | 2017 |
| Ashdown Reinforcing LLP | | 2012 |
| Ashdown Steel Limited | Construction | 2010 |
| Ashdown Surveying Ltd | Professional & scientific | 2011 |
| Asher Planning Ltd | Professional & scientific | 2012 |
| Ashfodon Properties Limited | Real estate | 2002 |
| Aspire Farm School Ltd | Education | 2024 |
| ASR+ Ltd | Education | 2020 |
| AST Spacemobile UK Limited | Information & communication | 2020 |
| Asterism Limited | Construction | 2017 |