| Association of Muslim Schools, UK | Education | 2003 |
| Association of Muslim Supplementary Schools | Education | 2010 |
| Assure Regulatory Services Ltd | Professional & scientific | 2013 |
| Assured Roofing and Specialist Leadworks Limited | Construction | 2014 |
| Assvi Catering Ltd | Hospitality | 2023 |
| Assvi Kitchen and Bar Limited | Hospitality | 2026 |
| AST Security Ltd | Administrative & support | 2022 |
| Astar Heating Limited | Other services | 2015 |
| Astera Transport Ltd | Transport & logistics | 2026 |
| Asterion Technology Limited | Information & communication | 2023 |
| Asteroid Marketing Ltd | Professional & scientific | 2025 |
| Astore Ice Cream Limited | Hospitality | 2026 |
| Astracloud Limited | Information & communication | 2024 |
| Astretoc Limited | Wholesale & retail | 2025 |
| Astro Capital Ltd | Wholesale & retail | 2020 |
| Astro Properties (MK) Limited | Real estate | 2020 |
| Asvgroup Ltd | Professional & scientific | 2023 |
| Aswy Construction Ltd | Construction | 2020 |
| Aszan Limited | Administrative & support | 2014 |
| AT Construction Consultancy Ltd | Construction | 2026 |
| AT Furniture Store Ltd | Wholesale & retail | 2019 |
| AT Gill Enterprises Ltd | Information & communication | 2023 |
| AT Siam Limited | Hospitality | 2020 |
| Atar Estates Ltd | Real estate | 2021 |
| Atarah Essentials Ltd | Wholesale & retail | 2025 |
| Ataur Rahman Harun Limited | Hospitality | 2018 |
| ATD Investment Group Ltd | Real estate | 2023 |
| ATD Ltd | Professional & scientific | 2019 |
| Atelier 07 Ltd | Professional & scientific | 2025 |
| Atexpert Consulting Ltd | Information & communication | 2023 |
| Athar Consulting Limited | Information & communication | 2025 |
| Atheena Construction Ltd | Construction | 2024 |
| Athill Court Freeholders Limited | Households | 2000 |
| Athwal Services Limited | Administrative & support | 2018 |
| Atif Food Limited | Hospitality | 2025 |
| Atif Shah Estates Ltd | Real estate | 2026 |
| Atif Studio Ltd | Information & communication | 2024 |
| Atjk Locum Ltd | Health & social care | 2021 |
| ATK Heating Services Ltd | Construction | 2025 |
| ATL Trans Limited | Transport & logistics | 2015 |
| Atlantic Medic Umbrella Limited | Professional & scientific | 2016 |
| Atlantis Space Ltd | Manufacturing | 2025 |
| Atlantis Travel Ltd | Administrative & support | 2014 |
| Atlas Aircraft Limited | Manufacturing | 2007 |
| Atlas Global Marketing Limited | Professional & scientific | 2025 |
| Atlas Group Solutions Ltd | Professional & scientific | 2020 |
| Atlas Hospitality Solutions Ltd | Professional & scientific | 2019 |
| Atlas Luton Limited | Transport & logistics | 2015 |
| Atlas Transporte Ltd | Other services | 2018 |
| ATO Holdings Limited | Agriculture & fishing | 1951 |
| Atob Cars (Dunstable) Limited | Administrative & support | 2011 |
| Atob Executive Ltd | Extraterritorial | 2013 |
| Atob Minibuses Ltd | Extraterritorial | 2013 |
| Atob Travel Ltd | Administrative & support | 2013 |
| Atom Cleaning Ltd | Administrative & support | 2015 |
| Atomikon Trading Company Limited | Manufacturing | 2026 |
| Atrata Traders Ltd | Wholesale & retail | 2025 |
| ATS Real Estate Ltd | Real estate | 2023 |
| Atsumi Capital Ltd | Real estate | 2021 |
| ATT10TIVE Social Enterprise CIC | Education | 2023 |
| Attainment Plus Tuition Ltd | Education | 2014 |
| Attar Apparel 1 Limited | Wholesale & retail | 2021 |
| Attar Apparel Limited | Wholesale & retail | 2021 |
| Attban Ltd | Other services | 2025 |
| Attila Transport Ltd | Transport & logistics | 2014 |
| Attire Blanche Limited | Wholesale & retail | 2024 |
| Attis Zeus Ltd | Hospitality | 2020 |
| Attnor Limited | Health & social care | 2014 |
| Attribute Design Limited | Professional & scientific | 2018 |
| Attwaterhouse Ltd | Professional & scientific | 2024 |
| ATV Acethatvisuals Ltd | Information & communication | 2022 |
| AU Seize Ltd | Wholesale & retail | 2021 |
| Aubrey Gardens Luton Limited | Households | 2011 |
| AUC Cleaning Services Ltd | Extraterritorial | 2023 |
| AUC Development Ltd | Construction | 2025 |
| AUC Property Investments Limited | Real estate | 2023 |
| AUC Property Sourcing Limited | Real estate | 2023 |
| Auction House Properties Ltd | Real estate | 2023 |
| Audacity of Hope Limited | Real estate | 1991 |
| Audio Video Limited | Information & communication | 2016 |
| Audit Edge Ltd | Professional & scientific | 2025 |
| Audrey Roberts Limited | Administrative & support | 2017 |
| Auera Holdings Ltd | Financial services | 2025 |
| Auggem Investments Limited | Financial services | 2026 |
| Auggem Limited | Hospitality | 2026 |
| August Martyn Accountants Limited | Professional & scientific | 2020 |
| August Martyn Associates Limited | Real estate | 2021 |
| Aujla Superstore (Luton) Ltd | Wholesale & retail | 2005 |
| AUK Radio Ltd | Information & communication | 2015 |
| AUK Studios Ltd | Information & communication | 2019 |
| Aulakh Investments Limited | Real estate | 2015 |
| Auora Trade LLP | | 2024 |
| Aura Aesthetic Academy Ltd | Health & social care | 2025 |
| Aura Reformer Ltd | Arts & recreation | 2026 |
| Aura Soleil Limited | Manufacturing | 2025 |
| Auraglasses Ltd | Wholesale & retail | 2026 |
| Auravi Ltd | Other services | 2023 |
| Aurea Healthcare Ltd | Administrative & support | 2025 |
| Aurek Ltd | Wholesale & retail | 2026 |
| Aurelia Carer Limited | Health & social care | 2017 |