| AJV Designs Ltd | Construction | 2014 |
| AJW Building Ltd | Construction | 2020 |
| AJW Property Management Limited | Construction | 2017 |
| AK Capital Estates Ltd | Real estate | 2026 |
| AK Facades Ltd | Construction | 2025 |
| AK Installation Ltd | Administrative & support | 2016 |
| AK Locksmiths & Security Solutions Limited | Other services | 2026 |
| AK Solent Property Holdings Ltd | Real estate | 2026 |
| Akaal Property Development Ltd | Real estate | 2015 |
| Akasya Ltd | Financial services | 2025 |
| AKAY1 Limited | Other services | 2026 |
| AKAY25 Limited | Other services | 2025 |
| Akbar Technologies Limited | Information & communication | 2018 |
| Akenzworldwide Limited Limited | Health & social care | 2022 |
| Akhirati Ltd | Wholesale & retail | 2025 |
| Akinscoper Ltd | Health & social care | 2020 |
| Akmr Holdings Ltd | Health & social care | 2026 |
| Akog Trading Limited | Wholesale & retail | 2025 |
| Akon Services Ltd | Transport & logistics | 2015 |
| Akrb Constructions Limited | Construction | 2025 |
| AKS Autos Southampton Ltd | Wholesale & retail | 2019 |
| AKS Carriers Ltd | Transport & logistics | 2026 |
| AKS Sunder Properties Ltd | Real estate | 2020 |
| Aksy Ltd | Real estate | 2023 |
| AKT Commercials Ltd | Wholesale & retail | 2022 |
| Akwamarine Limited | Arts & recreation | 2004 |
| AL Amin MUN Ltd | Information & communication | 2025 |
| AL Burooj Ltd | Wholesale & retail | 2024 |
| AL Connect Limited | Administrative & support | 2025 |
| AL Express Chef Ltd | Other services | 2014 |
| AL Forno Ristorante Limited | Hospitality | 2026 |
| AL GL Investments Ltd | Real estate | 2025 |
| AL Prestige Cars Limited | Wholesale & retail | 2020 |
| Al-Azzawi Businesses Limited | Real estate | 2022 |
| Al-Azzawi Trading Limited | Wholesale & retail | 2022 |
| Al-Ghais Traders Ltd | Wholesale & retail | 2026 |
| Al-Hq Law & More Ltd | Professional & scientific | 2021 |
| AL. Testing Limited | Professional & scientific | 2026 |
| Aladdin's Cave (Southampton) Ltd | Wholesale & retail | 2022 |
| Alam and SAN Ltd | Health & social care | 2016 |
| Alan Ball Academy Football Coaching Limited | Arts & recreation | 2026 |
| Alanbee Limited | Wholesale & retail | 2021 |
| Alaplas Limited | Wholesale & retail | 2022 |
| Alastair Stuart Ltd | Health & social care | 2021 |
| Alayah Limited | Wholesale & retail | 2024 |
| Albacore Software Limited | Information & communication | 1992 |
| Albacore Systems Limited | Information & communication | 1992 |
| Albany Park Court (Winn Road, Southampton) Residents Association Limited | Households | 2003 |
| Albatrostar Ukeig | | 2009 |
| Albert Court (Southampton) RTM Company Limited | Households | 2024 |
| Albert Court Southampton Limited | Households | 2005 |
| Alberto Homes Limited | Real estate | 2000 |
| Albibi Ltd | Transport & logistics | 2016 |
| Albion Forest Ltd | Financial services | 2020 |
| Albion Lettings Ltd | Real estate | 2026 |
| Albion Place Residents Company Limited | Households | 2002 |
| Alca & Co. Ltd | Professional & scientific | 2012 |
| Alcarol Ltd | Hospitality | 2026 |
| Alchemas Management Limited | Administrative & support | 2017 |
| Alchemeda Ltd | Wholesale & retail | 2024 |
| Alchemy Aesthetics Skin Clinic Ltd | Health & social care | 2019 |
| Alchemy Training Ltd | Arts & recreation | 2007 |
| Alchimea Properties Trading Limited | Real estate | 2018 |
| Alcohol Express Limited | Transport & logistics | 2021 |
| Alcon's Team Ltd | Construction | 2023 |
| Alden Sheetmetal Fabrications Limited | Manufacturing | 1984 |
| Alder Properties (Southampton) Ltd | Real estate | 2023 |
| Alder Trust | Health & social care | 2013 |
| Aldermoor Flat Management Company I Limited | Households | 1995 |
| Aldermoor Flat Management Company II Limited | Households | 1995 |
| Alders Court Management Company Limited | Households | 1986 |
| Aldridge Installations Ltd | Construction | 2013 |
| ALE & NIK Haulage. Ltd | Transport & logistics | 2022 |
| ALE Solutions Ltd | Professional & scientific | 2024 |
| Alec Bradley Services Ltd | Agriculture & fishing | 2022 |
| Alec Court Management Company Limited | Households | 1982 |
| Aleccom Limited | Transport & logistics | 2012 |
| Alefra Ukeig | | 2011 |
| Alegina Limited | Financial services | 2016 |
| Aleksander Ltd | Wholesale & retail | 2014 |
| Alemar Logistics Ltd | Transport & logistics | 2025 |
| Alemco Heating Services Limited | Construction | 2019 |
| Alenor Limited | Administrative & support | 2020 |
| Aletrans Ltd | Transport & logistics | 2015 |
| Alex Bowron Art Limited | Arts & recreation | 2024 |
| Alex Chilton Design Limited | Arts & recreation | 2006 |
| Alex Fotea Limited | Transport & logistics | 2018 |
| Alex GUY Photography Limited | Professional & scientific | 2010 |
| Alex King Entertainment Limited | Information & communication | 2025 |
| Alex Lisnic Ltd | Transport & logistics | 2025 |
| Alex Murray Education Consultancy Limited | Education | 2025 |
| Alex Shopfitting Limited | Construction | 2025 |
| Alex Smarter Ltd | Transport & logistics | 2022 |
| Alex Speed Line Ltd | Transport & logistics | 2026 |
| Alex&Vladut Ltd | Transport & logistics | 2024 |
| Alex's World Limited | Construction | 2019 |
| Alexa Alin Logistics Ltd | Transport & logistics | 2017 |
| Alexander Court (Southampton) Management Limited | Households | 1984 |
| Alexander Engineering Solutions Ltd | Manufacturing | 2024 |
| Alexander Hadleigh Wine Merchants and Importers Limited | Wholesale & retail | 1984 |