| Adaptiverf Limited | Manufacturing | 2008 |
| Adastra Communications Ltd | Professional & scientific | 2016 |
| Adcone Limited | | 1984 |
| ADD Agility Ltd | Information & communication | 2019 |
| ADD Space Self Storage Limited | Transport & logistics | 2000 |
| Addco Services Limited | Transport & logistics | 2016 |
| Adder PUB Company Limited | Hospitality | 2020 |
| Addgrange Limited | Households | 1985 |
| Addison Estate Agents Limited | Real estate | 2024 |
| Addison Facility Management Limited | Households | 2011 |
| Addison VEX Ltd | Information & communication | 2015 |
| Addos Consulting Limited | Professional & scientific | 2003 |
| Address: Movement for Social Change CIC | Arts & recreation | 2023 |
| Addsum Limited | Professional & scientific | 2015 |
| Addventure Leisure Limited | Administrative & support | 2021 |
| Addy Home Improvements Ltd | Construction | 2023 |
| Addy Transport Limited | Transport & logistics | 2025 |
| Adefol Limited | Households | 2022 |
| Adel M Foods Limited | Hospitality | 2024 |
| Adelaide Clarks Ltd | Wholesale & retail | 2017 |
| Adelaide Road 1963 Limited | Extraterritorial | 2014 |
| Adelaide Veterinary Clinic | | 1994 |
| Adem's Catering Ltd | Hospitality | 2025 |
| Adem’S Cafe Limited | Hospitality | 2020 |
| Adenaya Homes & Properties Ltd | Real estate | 2024 |
| Adenaya Solutions Ltd | Professional & scientific | 2020 |
| Adeon Creative Limited | Professional & scientific | 2016 |
| Adeon Group Limited | Extraterritorial | 2020 |
| Adeon Hospitality Limited | Extraterritorial | 2020 |
| Adeon Media Limited | Extraterritorial | 2020 |
| Adeon Spirits Limited | Extraterritorial | 2020 |
| Adepoju&Co Ltd | Health & social care | 2022 |
| Adept Accountancy and Consultancy Services Limited | Professional & scientific | 2022 |
| Adept Bars & Events Limited | Hospitality | 2010 |
| Adept RF Limited | Information & communication | 2013 |
| Adeptus Group Ltd | Construction | 2020 |
| Adeptus Limited | Real estate | 1960 |
| Adesso Coffee Bar Limited | Wholesale & retail | 2022 |
| ADG Property Maintenance Ltd | Administrative & support | 2019 |
| Adhiyamaan Foods Ltd | Hospitality | 2020 |
| Adira Property Management Ltd | Real estate | 2023 |
| Adiuvo Consultancy Ltd | Professional & scientific | 2024 |
| Adkins Refrigeration Limited | Manufacturing | 2010 |
| ADL Renovations Limited | Real estate | 2016 |
| Admin and Tonic Ltd | Hospitality | 2026 |
| Administration Management Consultants Limited | Administrative & support | 2026 |
| Admiral House (Warsash) Management Company Limited | Households | 1999 |
| Admiral Tapes Limited | Manufacturing | 1981 |
| Admirals Wharf (Southampton) Management Company Limited | Households | 2023 |
| Admiralty House Management Company Limited | Households | 2003 |
| Adnan Al-Badri Limited | Health & social care | 2011 |
| Adobson LLP | | 2023 |
| Adoptland Limited | Construction | 1983 |
| Ador Garage Doors Ltd | Construction | 2019 |
| Adorably Insane Ltd | Wholesale & retail | 2025 |
| Adoran Fish and Meat Ltd | Wholesale & retail | 2023 |
| Adornxclusive Craft House Limited | Wholesale & retail | 2026 |
| Ados-K Facilities Management Services Limited | Construction | 2024 |
| Adotive Ltd | Wholesale & retail | 2025 |
| ADP Architects Limited | Professional & scientific | 2002 |
| ADR Global Services Limited | Administrative & support | 2023 |
| Adrees Manier Ltd | Wholesale & retail | 2025 |
| Adrian Concept Construction Ltd | Construction | 2026 |
| Adrian Ionut Healthcare Ltd | Health & social care | 2020 |
| Adriatic Tanker Limited | Transport & logistics | 2022 |
| Adroit Contracting Ltd | Construction | 2019 |
| ADS Cooling Ltd | Energy | 2006 |
| ADS Properties (Southern) Ltd | Real estate | 2019 |
| ADS Recruitment Limited | Administrative & support | 1999 |
| ADS Recruitment Services Limited | Administrative & support | 2026 |
| ADS Uk-Properties Ltd | Real estate | 2024 |
| Adultcareservices Limited | Administrative & support | 2007 |
| Adur Medical Limited | Wholesale & retail | 2005 |
| Advance Management Solutions Ltd | Professional & scientific | 2023 |
| Advance PSC Limited | Information & communication | 2025 |
| Advance Yacht Holdings Limited | Wholesale & retail | 2022 |
| Advanced Auto Key Solutions LLP | | 2025 |
| Advanced AV Services Limited | Manufacturing | 2013 |
| Advanced Cardiology Care Ltd | Health & social care | 2022 |
| Advanced Clean Ltd | Administrative & support | 2012 |
| Advanced Covers Limited | Manufacturing | 2008 |
| Advanced Decor Ltd | Construction | 2014 |
| Advanced Digital Security Technology Ltd | Wholesale & retail | 2006 |
| Advanced Group XYZ Ltd | Wholesale & retail | 2025 |
| Advanced KFS Fabrication Limited | Professional & scientific | 2016 |
| Advanced Marine Decking Limited | Manufacturing | 2006 |
| Advanced Minibus Limited | Professional & scientific | 2009 |
| Advanced Services (Southampton) Limited | Construction | 2007 |
| Advanced Simulation Research | Arts & recreation | 2016 |
| Advanced Systems Understanding Ltd | Professional & scientific | 2012 |
| Advanced Timber Systems Limited | Construction | 2011 |
| Advanced Water Softeners Limited | Water & waste | 2003 |
| Advanced Watering Systems Ltd | Administrative & support | 2023 |
| Advancelets Limited | Real estate | 2014 |
| Advantage 2 Limited | Real estate | 2024 |
| Advantage Education Recruitment Limited | Administrative & support | 2025 |
| Advantage Grab Hire Ltd | Construction | 2025 |
| Advantec Limited | Construction | 2006 |
| Adventure Guardians Limited | Other services | 2016 |
| Adventures 4 Life South C.I.C. | Education | 2021 |