| A.P.S Welding & Fabrication Services Limited | Professional & scientific | 2010 |
| A.R. Wills Limited | Real estate | 1937 |
| AA Hughes Limited | Financial services | 2017 |
| AA Surgery Ltd | Health & social care | 2022 |
| Aadhira Limited | Health & social care | 2022 |
| Aarvold Health Limited | Health & social care | 2020 |
| Abbey Cars (Romsey) Ltd | Transport & logistics | 2012 |
| Abbey Chiropractic Clinic Limited | Health & social care | 2017 |
| Abbey Sprays Limited | Wholesale & retail | 2012 |
| Abbotstone (ST Albans) Ltd | Real estate | 2014 |
| Abbotstone Property Services Limited | Real estate | 2010 |
| Abbotswood Automation Ltd | Information & communication | 2026 |
| ABC (Solent) Limited | Professional & scientific | 2011 |
| ABC Swimming and Coaching Ltd | Administrative & support | 2024 |
| Abel Environmental Services Limited | Construction | 1989 |
| ABM Global Limited | Other services | 2015 |
| Absolute Electrical Services Ltd | Construction | 2002 |
| ABU Enterprises Limited | Wholesale & retail | 2023 |
| Academy (Romsey) Limited | Arts & recreation | 2010 |
| Accounting HUT (New Forest) Limited | Administrative & support | 2019 |
| Accounting HUT (Romsey) Limited | Professional & scientific | 2023 |
| Accountinghut Group Limited | Professional & scientific | 2022 |
| Ace Liftaway Limited | Water & waste | 2001 |
| Ace Loos Limited | Professional & scientific | 2011 |
| Ace Skip Hire (Southern) Limited | Professional & scientific | 2010 |
| Ace Surgical Limited | Health & social care | 2012 |
| Achoiring Voices Ltd | Arts & recreation | 2025 |
| Acme 3H Limited | Administrative & support | 2016 |
| ACT Security Systems Limited | Administrative & support | 1998 |
| Activate OT Hampshire Ltd | Public administration | 2023 |
| AD Infinitum (Associates) Limited | Wholesale & retail | 2015 |
| AD Pack Media Ltd | Professional & scientific | 2019 |
| Adam LAY Studio Limited | Other services | 2003 |
| Adamco Ltd | Professional & scientific | 2026 |
| Adept Electrical Ltd | Construction | 2020 |
| Adexen Consulting Ltd | Financial services | 2012 |
| ADM & Co Holdings Ltd | Information & communication | 2024 |
| ADS Creations Ltd | Health & social care | 2012 |
| Advance Yacht Systems Limited | Wholesale & retail | 2004 |
| Advantage Value Holdings Ltd | Professional & scientific | 2025 |
| Advantage Value Ltd | Professional & scientific | 2024 |
| AE Insurance Brokers Limited | Financial services | 1982 |
| AEC Protection Education Ltd | Education | 2025 |
| AEC Protection Security Ltd | Administrative & support | 2024 |
| Aequalia Limited | Extraterritorial | 2014 |
| Aeronautica at Southampton Ltd | Extraterritorial | 2009 |
| Aeronautique Europe Limited | Transport & logistics | 2005 |
| Aet.Gb. Limited | Administrative & support | 2001 |
| AFA Surgical Limited | Health & social care | 2019 |
| Affinity Technology Limited | Administrative & support | 2019 |
| Agalmic Ltd | Financial services | 2019 |
| Agentdouble Limited | Real estate | 1991 |
| Agnat Property Limited | Construction | 2024 |
| AGT Solutions Limited | Administrative & support | 2013 |
| AHD Developments Ltd | Construction | 2023 |
| AHT Surgical Limited | Health & social care | 2021 |
| Aimee's Commercial and Domestic Cleaning Services Ltd | Administrative & support | 2025 |
| Air Land & Sea Medical Ltd | Wholesale & retail | 2025 |
| AIR4U Group Limited | Administrative & support | 2017 |
| AIR4U Ltd | Professional & scientific | 2014 |
| Airia Compressed Air Solutions Limited | Professional & scientific | 2009 |
| Airlock Aviation Limited | Administrative & support | 2005 |
| Airsys Communications Technology Limited | Wholesale & retail | 1991 |
| AJ Services & Build Ltd | Construction | 2026 |
| AJB Anaesthetic Services LLP | | 2026 |
| AJB Anaesthetics Limited | Health & social care | 2014 |
| AJF Property Limited | Real estate | 2018 |
| AKB Consultancy Management Ltd | Professional & scientific | 2019 |
| AKR Surgical Limited | Health & social care | 2012 |
| AL Clarke Limited | Professional & scientific | 2009 |
| Alanandsim Ltd | Wholesale & retail | 2024 |
| Albani Electrical Ltd | Construction | 2020 |
| Aldebaran Limited | Professional & scientific | 2025 |
| Alder Clinical Limited | Health & social care | 2020 |
| Alepen Limited | Wholesale & retail | 2017 |
| Alex Danson 15 Limited | Education | 2016 |
| Alex Kelly Limited | Health & social care | 2007 |
| Alex Kerslake Photography Limited | Professional & scientific | 2020 |
| Alex Nails and Beauty Limited | Other services | 2021 |
| Alexander Southwell Mortgage Services Limited | Financial services | 2019 |
| Alexandra Wharf RTM Company Ltd | Households | 2023 |
| Alfaz Estates Ltd | Real estate | 2022 |
| Alfie BLU Ltd | Real estate | 2018 |
| Alicorn Learning Ltd | Administrative & support | 2024 |
| ALL Boogie Limited | Wholesale & retail | 2020 |
| ALL Fireplaces Limited | Extraterritorial | 2011 |
| ALL Star Marketing Club Limited | Professional & scientific | 2015 |
| ALL Things English Limited | Wholesale & retail | 2005 |
| Allair Fabrications Limited | Manufacturing | 2010 |
| Allen Build & Development Ltd | Construction | 2006 |
| Allseal Cleaning Services Limited | Water & waste | 2015 |
| Almenarah Ltd | Health & social care | 2023 |
| Almondhill Ltd | Construction | 2017 |
| Alpha Empire Records Limited | Information & communication | 2023 |
| Alta Property Investments Limited | Real estate | 2026 |
| Alternative Trade Fenestration Ltd | Construction | 2023 |
| Alto Integra Wealth Management Limited | Financial services | 2025 |
| Altokay Properties Limited | Other services | 1970 |
| AMA Quantum Consulting Ltd | Professional & scientific | 2016 |
| Amac Consulting Ltd | Professional & scientific | 2017 |