| Anneka's Childcare Ltd | Health & social care | 2024 |
| Annetts & Reid Groundwork Ltd | Construction | 2023 |
| Annfield Tyres Limited | Wholesale & retail | 1985 |
| Anpg Transport Limited | Transport & logistics | 2025 |
| Antacoht Limited | Wholesale & retail | 2025 |
| Anthoc Ltd | Information & communication | 2025 |
| Anya Barber Limited | Other services | 2026 |
| Anya Katie Cosmetics Ltd | Other services | 2019 |
| AO Legal Consultants Limited | Administrative & support | 2013 |
| AP Developments (Northants) Ltd | Construction | 2020 |
| AP Transmissions Ltd | Wholesale & retail | 2020 |
| APA Performance Ltd | Wholesale & retail | 2017 |
| APC Logistics Ltd | Transport & logistics | 2017 |
| APE Accessories Ltd | Manufacturing | 2014 |
| Aperitif Dental Limited | Health & social care | 2007 |
| Apex Gutter & Drainage Limited | Extraterritorial | 1990 |
| APO Barber Ltd | Other services | 2023 |
| Apollo Tyres (UK) Sales Ltd. | Manufacturing | 1934 |
| Aponia Medical Limited | Administrative & support | 2025 |
| Apowap Limited | Transport & logistics | 2019 |
| Apparo Consulting Limited | Information & communication | 2020 |
| Apple Tree Day Nurseries (Burton Latimer) Ltd | Education | 2011 |
| Appliance Tech Repairs Ltd | Other services | 2022 |
| April Brothers Ltd | Manufacturing | 2018 |
| April Nest Ltd | Real estate | 2025 |
| April Rise UK Limited | Real estate | 2023 |
| APX Services Ltd | Information & communication | 2024 |
| Aqua Air Solutions Ltd | Construction | 2026 |
| Aquaserve Contracting Limited | Extraterritorial | 2020 |
| Aquaserve Fish Limited | Extraterritorial | 2020 |
| Aquaserve Maintenance Limited | Other services | 2017 |
| Aquaserve Management Limited | Other services | 2017 |
| Aquatite Plumbing & Heating Ltd | Construction | 2014 |
| Aquila Lakes Limited | Agriculture & fishing | 2022 |
| Aquila Land Holdings Limited | Financial services | 2019 |
| Aquila Roots Limited | Financial services | 2026 |
| Aquila TM Limited | Financial services | 2022 |
| Aquilax Ltd | Information & communication | 2023 |
| AR Auto Solutions Ltd | Wholesale & retail | 2025 |
| Arabella Beau Ltd | Other services | 2022 |
| Arabica Change Limited | Professional & scientific | 2018 |
| Arai Tech Limited | Information & communication | 2024 |
| Arbucc (Drum) Limited | Real estate | 2018 |
| ARC Building Service Contractors Ltd | Construction | 2021 |
| ARC Electrical Installations Ltd | Construction | 2021 |
| ARC Fire Protection Services Ltd | Construction | 2021 |
| Arc-Hub Ltd | Information & communication | 2020 |
| Archers General Builders Limited | Construction | 2010 |
| Arco Partnership Group Limited | Professional & scientific | 2026 |
| ARD Contracting Limited | Construction | 2022 |
| ARH Consulting Services Limited | Administrative & support | 2023 |
| Aries Life Safety Systems Limited | Construction | 2017 |
| ARK Digital Solutions Limited | Professional & scientific | 2020 |
| Armandas Malisauskas Limited | Extraterritorial | 2022 |
| Armertec Limited | Extraterritorial | 2023 |
| Aroden Consulting Ltd | Professional & scientific | 2019 |
| Aroma UK Trading Ltd | Wholesale & retail | 2025 |
| Arora Ventures Ltd | Administrative & support | 2024 |
| Around Again Ltd | Wholesale & retail | 2022 |
| ARP Group Holdings Ltd | Administrative & support | 2017 |
| Arris Group Limited | Professional & scientific | 2026 |
| Arsh & Sahib Ltd | Real estate | 2020 |
| Artsphere Limited | Other services | 2005 |
| Artur Niski Transport Limited | Transport & logistics | 2016 |
| Arun Khajuria Ltd | Health & social care | 2021 |
| Arycr Ltd | Construction | 2026 |
| Aryton Consultancy Services Ltd | Professional & scientific | 2024 |
| Arytrans Limited | Transport & logistics | 2018 |
| ASA Trans Ltd | Transport & logistics | 2019 |
| ASC Group Holdings Limited | Financial services | 2026 |
| ASC Thrapston Limited | Real estate | 2026 |
| Ascend SI Limited | Information & communication | 2026 |
| Asco Europe Limited | Information & communication | 2022 |
| ASG Vending Ltd | Wholesale & retail | 2026 |
| ASH and Noah Limited | Financial services | 2018 |
| ASH Carpentry Limited | Construction | 2016 |
| ASH Hill Consultancy Limited | Professional & scientific | 2019 |
| Ashan Property Limited | Financial services | 2007 |
| Ashhay Transport Ltd | Transport & logistics | 2019 |
| Ashr Ltd | Construction | 2002 |
| Ashvale Roofing Systems Ltd | Construction | 2011 |
| Ashwood Smoking Chips Limited | Manufacturing | 2002 |
| ASK Property Group (Teville Road) Ltd | Construction | 2021 |
| ASK Technologies Limited | Information & communication | 2021 |
| Askew Cooling & Electrical Ltd | Manufacturing | 2013 |
| Askew's Hairdressing Ltd | Other services | 2020 |
| Aslan Property Management Limited | Wholesale & retail | 2023 |
| ASM Professionals Ltd | Administrative & support | 2025 |
| Aspire Education England Limited | Education | 2017 |
| Aspire Travel England Limited | Administrative & support | 2025 |
| Asset Connect Limited | Wholesale & retail | 2025 |
| Assured Plumbing and Heating Limited | Construction | 2024 |
| Astar Living Ltd | Real estate | 2017 |
| Astraea Escapes Limited | Administrative & support | 2026 |
| Astwell Augers Limited | Manufacturing | 1982 |
| Astwell Augers Trustees Limited | Professional & scientific | 2017 |
| AT Transport Solutions Limited | Transport & logistics | 2008 |
| AT Vehicle Solutions Limited | Wholesale & retail | 2025 |
| ATB Servicing Ltd | Transport & logistics | 2019 |
| Aten Properties Ltd | Real estate | 2026 |