| Ashwater Forge and Foundry Limited | Manufacturing | 1981 |
| Ashwood Trees Ltd | Agriculture & fishing | 2023 |
| Asia Stars River 2021 Limited | Hospitality | 2021 |
| Asikom Limited | Information & communication | 1999 |
| Askew Land & Soil Limited | Professional & scientific | 2013 |
| ASL Consulting Ltd | Extraterritorial | 2011 |
| ASN1 Limited | Financial services | 2022 |
| Aspect Windows (Holdings) Limited | Financial services | 2000 |
| Aspect Windows (Western) Limited | Construction | 1985 |
| Aspectus PR Limited | Extraterritorial | 2011 |
| Aspen and Peak Limited | Administrative & support | 2026 |
| Aspire Building & Maintenance Ltd | Construction | 2019 |
| Aspire Property Investments Limited | Real estate | 2019 |
| Aspire Social Work Services Ltd | Health & social care | 2014 |
| Aspired Coaching Ltd | Professional & scientific | 2024 |
| ASSESS4SUCCESS Limited | Professional & scientific | 2004 |
| Asset Direction Limited | Extraterritorial | 2006 |
| Asset Finance Specialists Ltd | Financial services | 2019 |
| Asset Worldwide Limited | Real estate | 2019 |
| Assinder Consulting Ltd | Professional & scientific | 2024 |
| Association "Moveup" CIC | Education | 2025 |
| Assured Children's Care Ltd | Real estate | 2022 |
| Assured Solar Ltd | Energy | 2020 |
| Aster Design Limited | Wholesale & retail | 2022 |
| Asterion PI Ltd | Manufacturing | 2023 |
| Aston House Ltd | Real estate | 1999 |
| Aston Reach Group Limited | Professional & scientific | 2026 |
| Astor Hall Limited | Health & social care | 2007 |
| Astridges Catering Ltd | Hospitality | 2014 |
| Astro Ambiance Ltd | Wholesale & retail | 2024 |
| Asurv Limited | Real estate | 2007 |
| Asymmetric Holdings Ltd | Financial services | 2024 |
| Asymmetric Solutions Limited | Professional & scientific | 2003 |
| ASZ ICT Consultancy Services Ltd | Information & communication | 2016 |
| AT Assets Ltd | Real estate | 2024 |
| AT Group (SW) Ltd | Construction | 2022 |
| AT Investment Developments Limited | Real estate | 2023 |
| AT Investment Holdings Limited | Professional & scientific | 2023 |
| AT Investment Property Limited | Real estate | 2023 |
| AT Property Holdings Limited | Financial services | 2017 |
| Atass Limited | Information & communication | 2003 |
| Atass Solar Limited | Administrative & support | 2010 |
| Atelier Real Estate Advisory Limited | Professional & scientific | 2026 |
| Atelier Real Estate Consultancy LLP | | 2026 |
| Athelstan Estates Limited | Real estate | 2001 |
| Athena's Restaurant Limited | Hospitality | 2025 |
| ATI Enterprises Ltd | Professional & scientific | 2016 |
| ATI Investments and Holdings Ltd | Professional & scientific | 2015 |
| Atigb Ltd | Information & communication | 2010 |
| Atkin Floors Limited | Construction | 2026 |
| Atkinson Transport Consultant Limited | Transport & logistics | 2018 |
| Atlantes Landscapes Ltd | Administrative & support | 2016 |
| Atlantic Standard Limited | Real estate | 2026 |
| Atlas Software Limited | Information & communication | 2005 |
| Atman Plumbing & Heating Ltd | Construction | 2014 |
| Atom Devon Ltd | Administrative & support | 2022 |
| Atom Studio Ltd | Professional & scientific | 2015 |
| ATP Holdings Limited | Real estate | 2001 |
| Attentus Financial Planning Ltd | Financial services | 2024 |
| Attitude Festival Ltd | Arts & recreation | 2022 |
| Attomarker Limited | Professional & scientific | 2008 |
| Attwood Leisure Limited | Arts & recreation | 2018 |
| Atven Limited | Professional & scientific | 2017 |
| Atven Property 2 Limited | Real estate | 2022 |
| Atven Property Limited | Real estate | 2021 |
| ATW Bricklaying & General Building Limited | Construction | 2020 |
| AU Bullion South West Ltd | Administrative & support | 2024 |
| AUB South West Ltd | Wholesale & retail | 2025 |
| Aubyn Investments Ltd | Financial services | 2025 |
| Auction Inspire Limited | Real estate | 2026 |
| Audifani Ltd | Information & communication | 2018 |
| Audify Holdings Ltd | Real estate | 2024 |
| Audify Ltd | Health & social care | 2006 |
| Audio Surgery Limited | Wholesale & retail | 2022 |
| Audiology Services Limited | Health & social care | 2026 |
| Audiomaster Limited | Other services | 2007 |
| Augusta Court (Exeter) Limited | Households | 2002 |
| Aura Security Services & Event Support Ltd | Administrative & support | 2026 |
| Aurel Living Limited | Real estate | 2025 |
| Aurora Ventures Limited | Administrative & support | 2011 |
| Aurora Vortem Group Ltd | Wholesale & retail | 2025 |
| Aurum Investments Limited | Financial services | 2004 |
| Auspex Systems Limited | Information & communication | 2016 |
| Austin and Dodd Ltd | Construction | 2024 |
| Austin Asset Management Ltd | Financial services | 2008 |
| Austra International Ltd | Wholesale & retail | 2024 |
| Austral Thinking Ltd | Professional & scientific | 2018 |
| Auter Tools Limited | Wholesale & retail | 2025 |
| Authentic Leadership Ltd | Professional & scientific | 2026 |
| Authentic Self Counselling Services Limited | Health & social care | 2022 |
| Authentisci Limited | Information & communication | 2023 |
| Autiverse Ltd | Wholesale & retail | 2025 |
| AUTM8 Ltd | Information & communication | 2026 |
| Auto Cleanse Services Ltd | Administrative & support | 2021 |
| Auto Shine Car Wash Limited | Wholesale & retail | 2018 |
| Autocamp Limited | Wholesale & retail | 2021 |
| Autocare Services (Exeter) Limited | Wholesale & retail | 2012 |
| Autoillusion(Exe) Ltd | Wholesale & retail | 2024 |
| Automettech Ltd | Professional & scientific | 2024 |
| Automigo Ltd | Manufacturing | 2026 |