| Affinis Limited | Professional & scientific | 2004 |
| Affinity Insurance Services Limited | Financial services | 1999 |
| AGE UK Portsmouth | Other services | 1996 |
| Agee Enterprise Limited | Transport & logistics | 2019 |
| AGO Chalcroft Limited | Real estate | 2018 |
| AGW Consultancy Ltd | Professional & scientific | 2006 |
| Ahmt Limited | Real estate | 2002 |
| Aircon Hire South Coast Limited | Administrative & support | 2006 |
| AJS Projects Ltd | Construction | 2003 |
| AKM Technologies Limited | Information & communication | 2002 |
| Akme Holdings Limited | Other services | 2006 |
| Aksum Polo Stud Limited | Agriculture & fishing | 2017 |
| Alan Price Motors Ltd | Wholesale & retail | 2004 |
| Alandown Motors Limited | Wholesale & retail | 1996 |
| Albert Road Boxing Club Limited | Arts & recreation | 2025 |
| Alders Electrical Services Limited | Construction | 2003 |
| Aldershot Specsavers Limited | Wholesale & retail | 1995 |
| Aldershot Valeting Centre Ltd | Other services | 2018 |
| Alington Estates Limited | Construction | 1955 |
| Alisfareham Ltd | Hospitality | 2023 |
| ALL Bright Electrical Limited | Construction | 2004 |
| ALL Keyed UP Ltd | Wholesale & retail | 2023 |
| ALL Plumbing Services Limited | Construction | 1998 |
| ALL Solution Products Limited | Wholesale & retail | 2003 |
| ALL Wessex Contract Cleaning Limited | Administrative & support | 2007 |
| Alliance Capital Management Limited | Real estate | 2000 |
| Alliance Warehouse Ltd | Wholesale & retail | 2023 |
| Alliott Wingham Limited | Professional & scientific | 2003 |
| Allstyles Scooters Limited | Wholesale & retail | 2000 |
| Alma Ventures Limited | Manufacturing | 2000 |
| Alpha Care Plus Ltd | Health & social care | 2022 |
| Alpha Next Consultancy Ltd | Professional & scientific | 2025 |
| Alsoils + Ltd | Agriculture & fishing | 2006 |
| Alstin Developments Limited | Construction | 1986 |
| Alternate Ending's Limited | Professional & scientific | 2002 |
| Alternative Audio Visual Limited | Transport & logistics | 1986 |
| Alternative Outdoor Ltd | Wholesale & retail | 2006 |
| Alternative Power Solutions Limited | Manufacturing | 2006 |
| Alysha Ltd | Other services | 2016 |
| Amada Investments Limited | Financial services | 2025 |
| Amaze Marketing Limited | Professional & scientific | 2002 |
| Ambassador Plant Hire Limited | Administrative & support | 2002 |
| Ambassador Pools and Leisure Limited | Administrative & support | 1997 |
| Amber Pictures Limited | Information & communication | 2003 |
| Amberley Stores Limited | Wholesale & retail | 1962 |
| AML Baby Care Limited | Health & social care | 2003 |
| Ammp Technology Ltd | Information & communication | 2023 |
| Amos Danby & Sons (Shopfitting) Limited | Wholesale & retail | 1997 |
| Amplespace Ltd | Professional & scientific | 1994 |
| AMR (UK) Limited | Wholesale & retail | 2005 |
| AMR Cybersecurity Ltd | Information & communication | 2018 |
| Amtevents Ltd | Administrative & support | 2020 |
| AN4 Networks Limited | Extraterritorial | 1994 |
| AND Publishing (South) Limited | Manufacturing | 2005 |
| Andark Promotions Limited | Wholesale & retail | 1976 |
| Andover Visionplus Limited | Wholesale & retail | 1991 |
| Andy Ruff Limited | Agriculture & fishing | 2003 |
| Anglo-French Marketing Services Limited | Professional & scientific | 2003 |
| Anjam Limited | Professional & scientific | 1997 |
| Anna Valley IT Services Limited | Professional & scientific | 2006 |
| Anne Sutherland Costing Limited | Professional & scientific | 2006 |
| Antoine Semenyo Co. Ltd | Administrative & support | 2026 |
| Antonio Marie Claret Ventures Ltd | Health & social care | 2015 |
| Antrobus House Limited | Real estate | 2006 |
| ANY Fish Limited | Manufacturing | 2001 |
| AP3D Solutions Limited | Manufacturing | 2021 |
| Apex Motorsport Marketing Ltd | Professional & scientific | 1995 |
| Apollo Fire Detectors Limited | Manufacturing | 1980 |
| Apparent Systems Limited | Information & communication | 2000 |
| Appnova Technology Limited | Information & communication | 2010 |
| Aqua Mare Limited | Administrative & support | 2002 |
| Aqualine Marketing Limited | Real estate | 2004 |
| Aran Consultants Ltd | Professional & scientific | 2025 |
| ARC Hairdressing Limited | Other services | 2002 |
| Ardington Group Limited | Wholesale & retail | 1993 |
| Arfonia Group Ltd | Wholesale & retail | 2025 |
| Ariel (U.K.) Limited | Financial services | 1971 |
| Arjo Wiggins Thermal Papers Limited | Transport & logistics | 1941 |
| ARK Medical Trust | Education | 1994 |
| ARK Specialist Services Ltd | Professional & scientific | 2007 |
| Arqiva Communications Limited | Information & communication | 1994 |
| Arqiva Defined Benefit Pension Plan Trustees Limited | Professional & scientific | 2004 |
| Arqiva Limited | Information & communication | 1990 |
| Arqiva Media Limited | Professional & scientific | 1993 |
| Arqiva NO 10 Limited | Professional & scientific | 2005 |
| Arqiva NO 11 Limited | Professional & scientific | 2005 |
| Arrowcroft Properties Limited | Real estate | 1999 |
| Arun Projects Limited | Construction | 2004 |
| AS Waite & SON Ltd | Construction | 2023 |
| Asembl AG Limited | Professional & scientific | 2001 |
| ASH Radford Limited | Arts & recreation | 2023 |
| Ashburton Court Management Company Limited | Hospitality | 1962 |
| Ashby Thompson & Thompson and Alldays Stores Limited T/A SAN Diego Road Gosport | | 1995 |
| Ashdale Engineering (Hampshire) Limited | Manufacturing | 1994 |
| Ashdene Homes Limited | Construction | 1987 |
| Aspire Learning and Development Limited | Professional & scientific | 2005 |
| Aspiro Education Limited | Education | 2006 |
| Asprey Systems Ltd | Information & communication | 1995 |
| Asset Finance and Management Limited | Professional & scientific | 1983 |
| Asset Management (2020) Limited | Financial services | 2020 |