| Arcane Consulting Ltd | Professional & scientific | 2026 |
| Arch a Media Limited | Professional & scientific | 2025 |
| Arch'Eng L Design Limited | Professional & scientific | 2015 |
| Architecture PLB Limited | Professional & scientific | 1989 |
| Ardema D&B Limited | Construction | 2025 |
| Argenson Limited | Arts & recreation | 2026 |
| Argent Invest Ltd | Other services | 2011 |
| Aries Farming LLP | | 2010 |
| Aristocrat FLY Fishing & Heritage FLY Tying CIC | Manufacturing | 2026 |
| ARJ Plumbing & Heating Services Ltd | Construction | 2018 |
| ARK Glass Glazing Contractors Ltd | Construction | 2002 |
| Arlebury Park House Estate Management Company Limited | Households | 1996 |
| Arlen Reed Interiors Ltd | Professional & scientific | 2026 |
| Armatus Consulting Ltd | Professional & scientific | 2025 |
| Armc Ltd | Professional & scientific | 2015 |
| Armex Energy Solutions Ltd | Construction | 2025 |
| Armichi Ltd | Other services | 2020 |
| Arnold Project Management Services Limited | Construction | 2020 |
| Arqiva Broadcast Finance PLC | Professional & scientific | 2012 |
| Arqiva Broadcast Intermediate Limited | Professional & scientific | 2012 |
| Arqiva Broadcast Parent Limited | Professional & scientific | 2012 |
| Arqiva Financing NO 1 Limited | Professional & scientific | 2007 |
| Arqiva Financing NO 2 Limited | Professional & scientific | 2007 |
| Arqiva Financing NO 3 PLC | Professional & scientific | 2004 |
| Arqiva Financing PLC | Professional & scientific | 2012 |
| Arqiva Group Holdings Limited | Professional & scientific | 2012 |
| Arqiva Group Intermediate Limited | Professional & scientific | 2012 |
| Arqiva Group Limited | Professional & scientific | 2004 |
| Arqiva Group Parent Limited | Professional & scientific | 2012 |
| Arqiva Holdings Limited | Professional & scientific | 1996 |
| Arqiva Intermediate Limited | Financial services | 2021 |
| Arqiva International Holdings Limited | Information & communication | 2013 |
| Arqiva Mobile TV Limited | Information & communication | 2000 |
| Arqiva Muxco Limited | Professional & scientific | 1989 |
| Arqiva Pension Trust Limited | Financial services | 1997 |
| Arqiva PP Financing PLC | Professional & scientific | 2013 |
| Arqiva Public Safety Limited | Professional & scientific | 1997 |
| Arqiva Satellite Limited | Information & communication | 1987 |
| Arqiva Senior Finance Limited | Professional & scientific | 2012 |
| Arqiva Smart Financing Limited | Information & communication | 2013 |
| Arqiva Smart Holdings Limited | Information & communication | 2013 |
| Arqiva Smart Metering Limited | Information & communication | 2013 |
| Arqiva Smart Parent Limited | Information & communication | 2013 |
| Arqiva Swing Limited | Information & communication | 2010 |
| Arqiva Telecoms Investment Limited | Information & communication | 1999 |
| Arqiva UK Broadcast Holdings Limited | Professional & scientific | 2004 |
| Arran Gate Limited | Households | 1992 |
| Arrow SIX Limited | Professional & scientific | 2024 |
| ARS IP Limited | Real estate | 2023 |
| ARS Traders Ltd | Wholesale & retail | 2011 |
| Art Psychotherapy Intervention and Cultivation Ltd | Health & social care | 2026 |
| Artemis Defence Consulting Ltd | Professional & scientific | 2017 |
| Artemis Earth Limited | Professional & scientific | 2024 |
| Artful Collective CIC | Administrative & support | 2020 |
| Arthur House Residents Association Limited | Hospitality | 2000 |
| Arthur's Court (Winchester) Ltd | Households | 2022 |
| ARTSCAN3D Ltd | Manufacturing | 2018 |
| Arturi Limited | Wholesale & retail | 1997 |
| Arun Prospect (Pulborough) Limited | Households | 1992 |
| Arun Valley Foods Limited | Professional & scientific | 2005 |
| Arundel Organics Limited | Professional & scientific | 2006 |
| Arzon Consulting Ltd | Information & communication | 2023 |
| AS Garden Supplies Limited | Wholesale & retail | 2018 |
| Asgil Limited | Financial services | 2023 |
| ASH Threading & Beauty Studio Ltd | Other services | 2024 |
| Ash's Advanced Autos Ltd | Wholesale & retail | 2025 |
| Ashbridge Partners Limited | Financial services | 2012 |
| Ashby Heritage Developments Ltd | Construction | 1940 |
| Ashcorn Estates Limited | Real estate | 1992 |
| Ashford Formwork Limited | Construction | 2009 |
| Ashton House (Winchester) Management Limited | Households | 1998 |
| Ashwood Trailer and Plant Ltd | Administrative & support | 2025 |
| Asian Food Hall Limited | Wholesale & retail | 2019 |
| Asian Niche House Ltd | Wholesale & retail | 2025 |
| Asisters Baby Limited | Education | 2026 |
| Asisters Limited | Other services | 2017 |
| Asoka Resources Limited | Professional & scientific | 2019 |
| ASP Corporate Ltd | Professional & scientific | 2017 |
| Aspen Carpentry Limited | Construction | 2005 |
| ASPIRE2 Limited | Arts & recreation | 2002 |
| ASPIRE4BUSINESS Academy Ltd | Education | 2020 |
| Aspirito Limited | Professional & scientific | 2007 |
| Asset Growth Investments Limited | Financial services | 2013 |
| Assore International Holdings Limited | Financial services | 2020 |
| Assure Pass Limited | Information & communication | 2009 |
| Asterclan Limited | Real estate | 1982 |
| Asteria Partners Ltd | Professional & scientific | 2013 |
| Astewt Consulting Limited | Professional & scientific | 2020 |
| Aston Enterprise UK Limited | Health & social care | 2018 |
| Aston Property Enterprise Limited | Real estate | 2018 |
| Astralis International Limited | Financial services | 2025 |
| Astrata Procure Ltd | Information & communication | 2020 |
| Astroflame (Fireseals) Limited | Manufacturing | 1994 |
| Astroflame Holdings Limited | Financial services | 2021 |
| Astron Properties Limited | Households | 1985 |
| AT Aviation Services Limited | Transport & logistics | 2023 |
| AT the Farm Limited | Education | 2018 |
| ATC Medical Services Ltd | Professional & scientific | 2024 |
| Atelier Winchester Limited | Financial services | 2026 |
| ATG Services (England) Limited | Professional & scientific | 2011 |