| Alpha Structural Engineering Limited | Real estate | 2025 |
| Alphacrux Ltd | Wholesale & retail | 2023 |
| Alpine Small Spaces Ltd | Construction | 2019 |
| Alpus Projects Limited | Real estate | 2019 |
| ALS Recruitment Limited | Administrative & support | 2017 |
| Alta VIA Bicycle Components Ltd | Wholesale & retail | 2025 |
| Altavia Homes Ltd | Construction | 2014 |
| Alternative Finance Solutions Limited | Professional & scientific | 2015 |
| Altin Property Ltd | Real estate | 2026 |
| Alton Primary Care Limited | Health & social care | 2022 |
| Altoona Securities Limited | Financial services | 1996 |
| Altruck Limited | Transport & logistics | 2016 |
| Alumain Ltd | Manufacturing | 2009 |
| Alver Park Management Company Limited | Households | 1998 |
| Alver-Stones Portsmouth Limited | Manufacturing | 2003 |
| Always Airports Group Limited | Transport & logistics | 2023 |
| Always Leasing Limited | Administrative & support | 2026 |
| Alyssa Wilk Growth Ltd | Wholesale & retail | 2025 |
| AM Libby Ltd | Administrative & support | 2025 |
| AMA Maritime Safety Ltd | Professional & scientific | 2025 |
| Amaafrique Foods UK Ltd | Wholesale & retail | 2025 |
| Amaco (PVT) Limited | Health & social care | 2013 |
| Amadeu London Ltd | Professional & scientific | 2025 |
| Amaliah Limited | Professional & scientific | 2015 |
| Amari International Investments Limited | Financial services | 2021 |
| Amark Care Ltd | Extraterritorial | 2025 |
| Amaya Swimwear Ltd | Wholesale & retail | 2024 |
| Amazing Lodge Limited | Real estate | 2024 |
| AMB Construction Services Ltd | Construction | 2020 |
| Amber Networks Ltd | Information & communication | 2017 |
| Amberley Court (Stubbington) Management Company Limited | Households | 2009 |
| Amberley Sports Limited | Arts & recreation | 2020 |
| Amberlu Engineering Limited | Professional & scientific | 2025 |
| Amberview Systems Limited | Information & communication | 2003 |
| Ambitio Limited | Construction | 2014 |
| Ambleside Court Telscombe Cliffs Limited | Households | 2006 |
| AMC Housing Limited | Real estate | 2024 |
| Amcob Limited | Administrative & support | 2013 |
| AME Partners Ltd | Health & social care | 2015 |
| Americana Aesthetics Ltd | Other services | 2026 |
| Amersham (Craneswater) RTM Company Limited | Real estate | 2016 |
| Amethyst Design Studio Ltd | Professional & scientific | 2021 |
| AMG Business Services Limited | Real estate | 2011 |
| AMG Industrial Roofing Ltd | Construction | 2007 |
| AMG Lettings & Developments Limited | Real estate | 2020 |
| Amicable Building Solutions Ltd | Construction | 2008 |
| Amico Portfolio Builders Ltd | Households | 2019 |
| AMJ Jointing Ltd | Energy | 2021 |
| Ammuro Limited | Professional & scientific | 2026 |
| Amos Copnor Limited | Hospitality | 2025 |
| AMP Electrical (Holdings) Limited | Wholesale & retail | 2016 |
| AMP Electrical Solutions Ltd | Construction | 2024 |
| AMP Electrical Supplies Limited | Wholesale & retail | 1994 |
| Ampthill House Limited | Real estate | 2012 |
| AMR Bookkeeping & Accounts Limited | Professional & scientific | 2006 |
| AMR Prime Limited | Administrative & support | 2017 |
| AMR Property Limited | Real estate | 2018 |
| AMR Services IOW Ltd | Construction | 2025 |
| AMR Spur Limited | Other services | 2013 |
| AMS Pipework Ltd | Construction | 2018 |
| Amufacture Ltd | Manufacturing | 2018 |
| AMW Assets Limited | Real estate | 2021 |
| AMY Carter Limited | Hospitality | 2016 |
| AMY Properties Development Company Ltd. | Construction | 2022 |
| Amynest Properties Limited | Real estate | 2020 |
| An.Vi.Ma. Ltd | Health & social care | 2021 |
| ANA Beauty Ltd | Other services | 2019 |
| ANA Treatment Centres Limited | Health & social care | 1999 |
| ANA Works C.I.C. | Other services | 2011 |
| Anatolia Kitchen Portsmouth Ltd | Hospitality | 2024 |
| Anatolia Turkish Kitchen Ltd | Hospitality | 2022 |
| Anca DC Ltd | Hospitality | 2026 |
| Anchor Point Storage Ltd | Transport & logistics | 2026 |
| Anchorage Property Developments Ltd | Construction | 2022 |
| Anchorheart Education Services Limited | Education | 2019 |
| Andair Limited | Manufacturing | 1995 |
| Anderson & Brett Ltd | Education | 2008 |
| Anderson Bone Electrical Limited | Real estate | 1998 |
| Andre and Fygle Properties Limited | Real estate | 2021 |
| Andrew & Andrew Solicitors Limited | Professional & scientific | 2015 |
| Andrew Clark Agencies Limited | Wholesale & retail | 2011 |
| Andrew Hammond Limited | Administrative & support | 2010 |
| Andrew Rivers Consulting Limited | Information & communication | 2010 |
| Andrew Smith Salons Limited | Other services | 2013 |
| Andrew Spencer Associates Ltd | Professional & scientific | 2018 |
| Andrew Zarb Healthcare Ltd | Health & social care | 2023 |
| Andrew Zarb Limited | Construction | 2018 |
| Andreza David Ltd | Real estate | 2019 |
| Andromeda Carpentry and Building Services Limited | Construction | 2004 |
| Andy Electrical Phone Shop Ltd | Wholesale & retail | 2023 |
| Andy GAS Southern Limited | Construction | 2003 |
| Andy Sills Motorcycles Limited | Wholesale & retail | 2024 |
| Anex (Portsmouth) Limited | Hospitality | 2018 |
| Anfield Court Management Limited | Real estate | 1999 |
| Angel Nails Portsmouth Ltd | Other services | 2024 |
| Angel's Care Support Ltd | Health & social care | 2021 |
| Angelic Relaxation Ltd | Health & social care | 2023 |
| Angels Property Development Ltd | Real estate | 2023 |
| Angels Southsea Limited | Hospitality | 2021 |
| Angels Support Limited | Health & social care | 2024 |