| April Ventures Limited | Information & communication | 2024 |
| APS Planning Ltd | Professional & scientific | 2016 |
| Aptnx Limited | Information & communication | 2021 |
| Aqueous Crewing Ltd | Administrative & support | 2025 |
| Aquvalue Limited | Information & communication | 2019 |
| AR Data & AI Limited | Information & communication | 2025 |
| Arborsphere Ltd | Professional & scientific | 2011 |
| ARC Support Limited | Administrative & support | 2022 |
| Arcanite Limited | Information & communication | 2007 |
| Arch Furniture Ltd | Manufacturing | 2011 |
| Arch International Ltd | Manufacturing | 2018 |
| Archmyle Limited | Professional & scientific | 2026 |
| Archway Recruitment Ltd | Administrative & support | 2025 |
| Arendor Consulting Ltd | Information & communication | 2022 |
| Aretus Ltd | Health & social care | 2019 |
| Argentic Intelligence Ltd | Professional & scientific | 2025 |
| Argonavis AI Limited | Information & communication | 2016 |
| Argyle Digital Limited | Professional & scientific | 2025 |
| ARH Technical Ltd | Professional & scientific | 2023 |
| Ari's Thread Limited | Professional & scientific | 2017 |
| Ariel Dorset Limited | Transport & logistics | 2022 |
| Arkezra Consult Ltd | Professional & scientific | 2013 |
| Arlington (Blandford) Limited | Construction | 2021 |
| Arlington Estates Ltd | Financial services | 2021 |
| Arlington Limited | Construction | 1992 |
| Arlington South Limited | Construction | 2014 |
| ARM Consulting Services Limited | Information & communication | 2007 |
| Armoured Property Ltd | Real estate | 2022 |
| Arnold Snell Building Ltd. | Construction | 2005 |
| Arocl Limited | Information & communication | 2023 |
| Aroma @ Wimborne Ltd | Hospitality | 2026 |
| Arqetec Ltd | Professional & scientific | 2015 |
| ARS Actuarial Ltd | Financial services | 2024 |
| Artactix Ltd | Information & communication | 2022 |
| Artek Digital Ltd | Information & communication | 2022 |
| Artemis Cloud Ltd | Information & communication | 2022 |
| Arten Advisory Group Ltd | Professional & scientific | 2025 |
| Arthouse Developments Limited | Construction | 2021 |
| Arvense Limited | Energy | 2019 |
| Aryaa Associates Ltd | Information & communication | 2009 |
| Asaltern Limited | Energy | 2019 |
| Asbery Softworks Ltd | Information & communication | 2022 |
| Ascalon Digital UK Limited | Information & communication | 2021 |
| Ascend IT Services Limited | Information & communication | 2021 |
| Ascent Business Brokers Limited | Professional & scientific | 2026 |
| Ascent Health Ltd | Information & communication | 2022 |
| Ascent Outsourcing Management Ltd | Information & communication | 2010 |
| Asecuro Solutions Ltd | Information & communication | 2024 |
| Asgs (UK) Ltd | Manufacturing | 2011 |
| Ashaah Limited | Professional & scientific | 2017 |
| Ashacre Consulting Limited | Information & communication | 2016 |
| Ashbolt Limited | Real estate | 1982 |
| Ashgate Consultancy Ltd | Professional & scientific | 2025 |
| Ashgrove (Marley) Wimborne Ltd | Real estate | 2016 |
| Ashington Gardens Management Co. Ltd. | Administrative & support | 1993 |
| Ashington Interiors Limited | Construction | 2014 |
| Ashman Accountancy Ltd | Professional & scientific | 2026 |
| Ashman Technology Ltd | Information & communication | 2011 |
| Ashwick Court and Barrington Court Management Company Limited | Households | 2018 |
| ASK Coatings Limited | Manufacturing | 2008 |
| ASK Poole Ltd | Real estate | 2022 |
| Asme Sales Limited | Wholesale & retail | 2020 |
| Aspens Swanage Freehold Limited | Households | 2010 |
| Aspire Professionals Ltd | Wholesale & retail | 2021 |
| Aspire Share Plans Ltd | Administrative & support | 2018 |
| Aspirin Business Solutions Limited | Professional & scientific | 2004 |
| Assure Service Solutions Limited | Information & communication | 2014 |
| Assurelogic Solutions Ltd | Information & communication | 2025 |
| Astech Environmental Limited | Construction | 2016 |
| Astmine Technical Ltd | Information & communication | 2022 |
| Astra Land Developments Ltd | Construction | 2026 |
| Astuco Ltd | Information & communication | 2023 |
| AT & BTC Properties Limited | Real estate | 2024 |
| AT Chiropractic Ltd | Professional & scientific | 2024 |
| AT Lets Ltd | Real estate | 2025 |
| ATC Contractors Limited | Construction | 2006 |
| Athena Datum Ltd | Professional & scientific | 2022 |
| Atinsy Limited | Information & communication | 2024 |
| Atkins Travel Limited | Administrative & support | 1988 |
| Atkinson Business Services Limited | Financial services | 2014 |
| Atlantic Coast Inns Ltd | Hospitality | 2025 |
| Atlas Analytics Limited | Information & communication | 2022 |
| Atlas Experts Ltd | Professional & scientific | 2021 |
| Atlas North Ltd | Professional & scientific | 2018 |
| Atlet (Dorset) Ltd | Real estate | 2025 |
| ATR15 Consulting Limited | Information & communication | 2020 |
| Atreus Accountants Ltd. | Professional & scientific | 2005 |
| Attila the Pubs Ltd | Hospitality | 2026 |
| Atzn Limited | Information & communication | 2016 |
| AU Supplements Ltd | Wholesale & retail | 2020 |
| Audience Digital Ltd | Information & communication | 2022 |
| Audit Fit Ltd | Professional & scientific | 2025 |
| Audlem Lodge Management Co Limited | Households | 2005 |
| Aufgabe Limited | Information & communication | 2019 |
| Aufgabe Services Limited | Real estate | 2022 |
| Augendae Limited | Professional & scientific | 2023 |
| Augustus Brandt Limited | Wholesale & retail | 2006 |
| Aunt Fannys Cafe Ltd | Hospitality | 2026 |
| Aunt Fannys Farm Shop Ltd | Hospitality | 2019 |
| Aunt Fannys Wimborne Ltd | Hospitality | 2023 |