| Aromacoherence CIC | Education | 2026 |
| Around the World Properties Limited | Real estate | 2024 |
| ARP Energy Services Ltd | Construction | 2016 |
| Arragon Digital Ltd | Professional & scientific | 2016 |
| Arrowshot Solutions Limited | Professional & scientific | 2014 |
| Arthurs Chiropody Ltd | Health & social care | 2020 |
| Artic Cool Limited | Transport & logistics | 2010 |
| Arts for Everyone Ltd | Hospitality | 2023 |
| Arunodaya Foods & Beverages Limited | Wholesale & retail | 2025 |
| Aruvida Limited | Wholesale & retail | 2023 |
| Arvida Limited | Real estate | 2002 |
| AS Chamoli Ltd | Hospitality | 2023 |
| AS Payroll Limited | Administrative & support | 2020 |
| AS Temps Limited | Administrative & support | 2019 |
| Ascend Global Investments Limited | Real estate | 2026 |
| Ascendant Events Ltd | Hospitality | 2024 |
| Aseda Property Ltd | Real estate | 2022 |
| Aservices UK Limited | Administrative & support | 2009 |
| ASG Prime Developments Ltd | Construction | 2023 |
| Asharma Mind Concepts Limited | Professional & scientific | 2023 |
| Asharma Properties Limited | Real estate | 2021 |
| Ashdav Consultant Ltd | Professional & scientific | 2023 |
| Ashingdon Heights Boarding Kennels Ltd | Other services | 2016 |
| Ashleigh Stone Estate Agents Limited | Real estate | 2014 |
| Ashleigh Stone Lettings Limited | Real estate | 2014 |
| Ashpd Ltd | Professional & scientific | 2025 |
| Asist.App Limited | Information & communication | 2026 |
| ASK ALI Limited | Information & communication | 2025 |
| Aspect Maintenance Ltd | Construction | 2003 |
| Aspect Paving & Groundworks Ltd | Construction | 2019 |
| Aspect Paving Ltd | Administrative & support | 2022 |
| Aspect Ventilation Ltd | Construction | 2019 |
| Aspire Cost Management Limited | Professional & scientific | 2020 |
| Aspire to Learn Limited | Education | 2007 |
| Aspis Protection Ltd. | Administrative & support | 2020 |
| Aspome Holdings Limited | Financial services | 2021 |
| Asquiths Social Care Services Limited | Health & social care | 2012 |
| Assembly Finishing Limited | Manufacturing | 2011 |
| Asset Interiors Ltd | Construction | 2021 |
| Asset Recovery Services Ltd | Transport & logistics | 2017 |
| Aster & Barnes Construction Management Limited | Construction | 2018 |
| Aster & Barnes Limited | Construction | 2017 |
| Astoms Ltd | Construction | 2014 |
| Astonrange Limited | Information & communication | 1992 |
| Astwood Resources Ltd | Professional & scientific | 2024 |
| AT Benfleet Ltd | Real estate | 2021 |
| Ataurus Ltd | Construction | 2025 |
| ATB Film Production Limited | Information & communication | 2024 |
| Atds Property Maintenance & Management Services Ltd | Construction | 2021 |
| ATG Cleaning Services Ltd | Administrative & support | 2023 |
| Athletica Fitness & Strength Ltd | Arts & recreation | 2022 |
| ATI Atlas Ltd. | Wholesale & retail | 1949 |
| ATK Property Rental Ltd | Real estate | 2019 |
| Atkins Roofworks Limited | Construction | 2014 |
| Atlas Advisors Limited | Professional & scientific | 2021 |
| Atlas Personal Wealth Management Ltd | Financial services | 2025 |
| Atom Consult Limited | Construction | 2026 |
| Aton Homes Limited | Real estate | 2018 |
| Atrios Designs Ltd | Construction | 2025 |
| Attech EDU Limited | Professional & scientific | 2017 |
| Attica Capital Ltd | Financial services | 2014 |
| Atwin Build Ltd | Construction | 2023 |
| Atwin Electrical Limited | Construction | 2013 |
| Atypical Architecture Ltd | Professional & scientific | 2022 |
| Aubepine Limited | Financial services | 2026 |
| Aubrey WIG Collective Limited | Other services | 2025 |
| Auction House Kent Limited | Hospitality | 2019 |
| Audio Rehab Group Limited | Information & communication | 2025 |
| Audio Solutions Ltd | Administrative & support | 2016 |
| Aura Buildings & Land Limited | Real estate | 2021 |
| Aura Partners Ltd | Wholesale & retail | 2025 |
| Aureus Asset Managers Limited | Financial services | 2010 |
| Aurium Limited | Information & communication | 2013 |
| Austin Anderson Limited | Construction | 1996 |
| Austin Stuart Project Management Ltd | Professional & scientific | 2015 |
| Austin Utilities & Groundworks Ltd | Construction | 2022 |
| Auto Lease Compare Ltd | Information & communication | 2018 |
| Auto Parts & Components Ltd | Wholesale & retail | 2026 |
| AUTOM8 AI Ltd | Professional & scientific | 2025 |
| Automotive CAD Design Limited | Professional & scientific | 2009 |
| Automotive Intelligence Ltd | Wholesale & retail | 2022 |
| AUTOPULSE360 Ltd | Information & communication | 2026 |
| Autostyle Performance Ltd | Wholesale & retail | 2022 |
| Autus Excel Consulting Limited | Professional & scientific | 2025 |
| Avacon Consulting Limited | Professional & scientific | 2021 |
| Avamae Software Solutions Ltd | Information & communication | 2011 |
| Aventier Developments Ltd | Professional & scientific | 2015 |
| Aventier Holding Limited | Other services | 2017 |
| Aventier Limited | Other services | 2016 |
| Avery Good Company Limited | Transport & logistics | 1997 |
| AVI Engineering Solutions Limited | Construction | 2016 |
| Aviahorizon Limited Liability Partnership | | 2002 |
| Avionicare Limited | Other services | 1989 |
| AVK Holdings Limited | Administrative & support | 2024 |
| Avocet Advisory Ltd | Administrative & support | 2018 |
| Avondale Court (Leigh-On-Sea) Management Company Limited | Households | 1988 |
| Avora Plus Limited | Professional & scientific | 2025 |
| Avra Windows Ltd | Construction | 2026 |
| AW Hospitality Group Ltd | Manufacturing | 2024 |
| Awdl Property Ltd | Households | 2025 |