| Altogether Care - Care at Home Limited | Health & social care | 2002 |
| Always Distribution 13 Limited | Wholesale & retail | 2013 |
| Alycia Aura Ltd | Wholesale & retail | 2025 |
| AM Salonservices Limited | Administrative & support | 2012 |
| AM Sport Consultants Limited | Arts & recreation | 2024 |
| Ambatek Limited | Other services | 2008 |
| AMC Gadda Limited | Professional & scientific | 2018 |
| Amelia Rose Holdings Ltd. | Professional & scientific | 2015 |
| Amelia Rose Wellbeing Limited | Other services | 2019 |
| Amerson Limited | Manufacturing | 1954 |
| AMG FM Solutions Limited | Construction | 2010 |
| AMH Safety Limited | Professional & scientific | 2023 |
| Amico (a. Medcroft Investment Company) Limited | Construction | 1989 |
| Amor Property Group Ltd | Real estate | 2026 |
| Amore Poole Ltd | Hospitality | 2016 |
| AMP GBR Ltd | Real estate | 2018 |
| AMY Tapper Limited | Arts & recreation | 2014 |
| Anafina Limited | Real estate | 2021 |
| ANB Electrical Limited | Construction | 2007 |
| Anchor Point SW Ltd | Construction | 2025 |
| Anchorage Holdings SW Limited | Financial services | 2021 |
| Anders Design LLP | | 2004 |
| Andrew Burton Photography Limited | Professional & scientific | 2017 |
| Andrew Sloan Holdings Limited | Financial services | 2020 |
| Andy Stevens Electrical Limited | Construction | 2007 |
| Andy Woodgate Driver Training Limited | Education | 2017 |
| Anetwork Limited | Information & communication | 2002 |
| Angel Estate Management Ltd | Real estate | 2017 |
| Angels 2020 Ltd. | Real estate | 2020 |
| ANM Plastering Limited | Construction | 2013 |
| Anna Beauty Limited | Other services | 2012 |
| Anna Bowen Ltd | Education | 2006 |
| Anna's Event Catering Limited | Hospitality | 2023 |
| Anomaly Engineering Limited | Professional & scientific | 1994 |
| Anteros Goodmayes Ltd | Hospitality | 2019 |
| Anthony Calleja Financial Solutions Limited | Financial services | 2026 |
| ANY Event Bars Limited | Hospitality | 2011 |
| AOK Airconditioning Limited | Manufacturing | 2015 |
| AP Electric Contractors Limited | Construction | 2014 |
| APC Bites Ltd | Hospitality | 2024 |
| Apex Catering Equipment Ltd | Wholesale & retail | 2003 |
| Apex Catering Weymouth Limited | Real estate | 2023 |
| Apex Diving and Marine Ltd | Transport & logistics | 2024 |
| Apex Power Limited | Construction | 2018 |
| Apex Scaffolding (Dorset) Limited | Construction | 2026 |
| Apollo Marine Systems Ltd | Agriculture & fishing | 2014 |
| Appleby Systems Ltd | Information & communication | 2021 |
| Applied Planning & Programme Management Services Ltd | Professional & scientific | 2021 |
| Aquae Sulis Chiropractic Clinic Ltd | Health & social care | 2015 |
| Aquarium Technology Limited | Manufacturing | 1996 |
| Aquavista RTM Company Ltd | Households | 2017 |
| Aquila Weymouth Ltd | Hospitality | 2024 |
| AR Accounting (Dorset) Limited | Professional & scientific | 2017 |
| Arbology Ltd | Professional & scientific | 2016 |
| Arcadia Technology Limited | Information & communication | 1997 |
| Arcuatura Ltd | Extraterritorial | 2023 |
| Arish Properties Limited | Real estate | 2009 |
| Arleco Holdings Ltd | Information & communication | 2023 |
| Arlo Labs Ltd | Wholesale & retail | 2025 |
| Arron Giffen Tree Surgery Limited | Administrative & support | 2015 |
| Arthur Fordham Ltd | Wholesale & retail | 2018 |
| Artisan (South) Ltd | Construction | 2019 |
| Artisan Build & Maintenance Limited | Construction | 2014 |
| Artisan Island Ltd | Other services | 2024 |
| Artistic Licence UK Limited | Arts & recreation | 2016 |
| Artrange Data Limited | Information & communication | 1992 |
| Arttechspace Limited | Information & communication | 2012 |
| AS and When Chef Services Ltd | Hospitality | 2019 |
| Ascari Event Consultants Limited | Professional & scientific | 2013 |
| ASH Care Devote Limited | Health & social care | 2023 |
| ASH Elite Limited | Professional & scientific | 2015 |
| Ashbee Home Care Ltd | Health & social care | 2022 |
| Ashmira Properties Ltd | Construction | 2025 |
| Ashton Leisure Limited | Hospitality | 2011 |
| Ashwell Lodge Limited | Health & social care | 2023 |
| Ashworth Decor Ltd | Construction | 2025 |
| Asiagold Ltd | Professional & scientific | 2015 |
| Aslanlar Limited | Hospitality | 2016 |
| Asmpt SMT UK Limited | Manufacturing | 1967 |
| Asmpt UK Holding Limited | Financial services | 2010 |
| Asone Theatre Company Ltd | Arts & recreation | 2017 |
| Aspen 25 Limited | Professional & scientific | 2025 |
| Aspen Management (Dorchester) Limited | Households | 2007 |
| Assurance Programme Solutions Limited | Professional & scientific | 2015 |
| Assured Technical Consulting Limited | Other services | 2018 |
| Atlantic Audio Limited | Administrative & support | 1997 |
| Atlantic Group (SW) Limited | Construction | 2024 |
| Atlantic Property Letting Limited | Real estate | 2023 |
| ATM Aviation Ltd | Manufacturing | 2018 |
| Auctoritas Ltd | Health & social care | 2022 |
| Audelab Ltd | Information & communication | 2026 |
| Aura Cafe Bar Ltd | Hospitality | 2010 |
| Autocare Weymouth Ltd | Wholesale & retail | 2022 |
| Automarine Services Limited | Real estate | 1988 |
| Automotive Armour Ltd | Wholesale & retail | 2023 |
| AV Travel Limited | Real estate | 1999 |
| Avalanche Management Company Limited | Real estate | 2018 |
| Avanti Sports Ltd | Arts & recreation | 2019 |
| Avenca Limited | Information & communication | 2001 |
| Avenue Estate Agents Limited | Real estate | 2018 |