| ACTIV8 Services Southern Ltd | Construction | 2022 |
| Active Bike Co Ltd | Wholesale & retail | 2020 |
| Active Information Systems Limited | Information & communication | 1998 |
| Active Physio Clinics Limited | Professional & scientific | 2003 |
| Active Property Deal Direct Limited | Real estate | 2015 |
| Active Social Club CIC | Health & social care | 2024 |
| ACTIVE8 Minds West Sussex Ltd | Education | 2024 |
| ACTIVEO3 Ltd | Administrative & support | 2024 |
| Actuation Engineering Ltd | Manufacturing | 2001 |
| Acumen Software Systems Ltd | Information & communication | 2023 |
| Acumen Ventures Limited | Professional & scientific | 2016 |
| AD Astra Cloud Services Limited | Professional & scientific | 2024 |
| Adam Foster Consulting Limited | Information & communication | 1999 |
| Adam James Bespoke Joinery Limited | Manufacturing | 2021 |
| Adam Wheatley 2019 Ltd | Financial services | 2019 |
| Adamas Investments Limited | Financial services | 2024 |
| Adams Integra Limited | Professional & scientific | 1997 |
| Adams Integra Viability Consultants Limited | Professional & scientific | 2018 |
| Adams Watt Ltd | Manufacturing | 2016 |
| Adanti Properties Ltd | Real estate | 2021 |
| Adapted Performance Ltd | Wholesale & retail | 2026 |
| Adarex Films Ltd | Information & communication | 2020 |
| ADC International Limited | Information & communication | 1992 |
| ADD Two Studio Ltd | Information & communication | 2024 |
| Addlot Limited | Hospitality | 1989 |
| Addressograph Limited | Wholesale & retail | 2009 |
| Adelaide CS Ltd | Hospitality | 2018 |
| Adept Construction (Sussex) Ltd | Construction | 2023 |
| Adept Projects Limited | Professional & scientific | 2023 |
| Adex Plus Ltd | Transport & logistics | 2015 |
| Adinvale Limited | Administrative & support | 2001 |
| ADM Electrical Sussex Ltd | Construction | 2021 |
| ADM Holdings Sussex Ltd | Financial services | 2025 |
| ADM Properties Sussex Ltd | Real estate | 2025 |
| ADM Special Projects Limited | Construction | 2015 |
| ADT Farriers Ltd | Agriculture & fishing | 2019 |
| Adur Valley Homes Limited | Construction | 2015 |
| Advance Surgical Ltd | Administrative & support | 2021 |
| Advanced Aviation and Marine Services Ltd | Administrative & support | 2022 |
| Advanced Medical Equipment Limited | Wholesale & retail | 2002 |
| Advanced Plastering Solutions Ltd | Construction | 2022 |
| Adventures in Arizona Ltd | Professional & scientific | 2005 |
| Advice for Later Life Ltd | Financial services | 2019 |
| Advice for Life Ltd | Financial services | 2024 |
| ADW Services 2019 Ltd | Real estate | 2019 |
| Aeacus Events Ltd | Hospitality | 2021 |
| AEL Home Improvements Ltd | Construction | 2024 |
| Aeneas Limited | Real estate | 2000 |
| Aeolian Ltd | Professional & scientific | 2020 |
| Aern Solutions Ltd | Information & communication | 2016 |
| Aerobility | Other services | 2012 |
| Aerofoils Limited | Wholesale & retail | 2023 |
| Aeromar Safety and Performance Ltd | Professional & scientific | 2026 |
| Aeronautics (UK) Ltd | Professional & scientific | 2019 |
| Aesop House Ltd | Professional & scientific | 2021 |
| Aethr Associates Limited | Professional & scientific | 2023 |
| Affirma Ltd | Professional & scientific | 2019 |
| AG Pharma Solutions Ltd | Health & social care | 2018 |
| AGD Groundworks Ltd | Construction | 2018 |
| AGE Sentinel Ltd | Professional & scientific | 2009 |
| Aggregate-Recycling (Southern) Ltd | Construction | 2021 |
| Agility AI Ltd | Information & communication | 2026 |
| Agks Holdings Ltd | Financial services | 2024 |
| AGO Dental Limited | Health & social care | 2025 |
| Agricultural Contracting Services Limited | Agriculture & fishing | 1983 |
| Agritrade-Ps Ltd | Wholesale & retail | 2018 |
| AGS Frozen Foods Ltd | Hospitality | 2003 |
| Agsl Ltd | Administrative & support | 2022 |
| AH Design Components Ltd | Professional & scientific | 2021 |
| Ahawkinstherapy Limited | Extraterritorial | 2021 |
| AHS Assets Limited | Administrative & support | 2019 |
| Aics Global Ltd | Information & communication | 2025 |
| Aidata Limited | Information & communication | 1995 |
| AIE Electrical Ltd | Construction | 2024 |
| Airfix Technical Services Ltd | Manufacturing | 2021 |
| Airport Cabs Express Ltd | Transport & logistics | 2024 |
| Airstem Limited | Financial services | 2014 |
| Airtight Studio's Limited | Information & communication | 1998 |
| Airworks Worldwide Ltd. | Transport & logistics | 2012 |
| Aiworkmatch Ltd | Administrative & support | 2026 |
| AJ Aviation Services Ltd | Education | 2026 |
| AJB Sales Ltd | Wholesale & retail | 2019 |
| AJL Projects Ltd | Manufacturing | 2020 |
| AJM Accounting Services Ltd | Professional & scientific | 2011 |
| AJS Contract Solutions Ltd | Professional & scientific | 2024 |
| AJT Financial Planning Ltd | Professional & scientific | 2024 |
| AK Fire & Safety Consulting Ltd | Financial services | 2017 |
| Akoka Ltd | Hospitality | 2026 |
| Akroyd Brown Limited | Other services | 2004 |
| Aladdins Cave Jewellery Limited | Wholesale & retail | 2015 |
| Alan Davis (Building Services) Limited | Construction | 1997 |
| Alan Green Limited | Administrative & support | 2003 |
| Albany Global Limited | Administrative & support | 2024 |
| Albatross Filtration Systems Ltd Limited | Water & waste | 2025 |
| Albion Properties (Brighton) Limited | Real estate | 2005 |
| Alco Leisure Limited | Administrative & support | 2009 |
| Alder Advisory Limited | Professional & scientific | 2022 |
| Aldford Properties Limited | Real estate | 2001 |
| Aldingbourne Accountancy Services Limited | Professional & scientific | 1984 |
| Aldingbourne Park Farm Lodges Ltd | Real estate | 2025 |