| Atin Skin Ltd | Other services | 2025 |
| Atinderpal Singh Ltd | Construction | 2025 |
| Atinta Group Ltd | Real estate | 2018 |
| Atis Group Ltd | Real estate | 2024 |
| Atithi Hospitality Ltd | Hospitality | 2018 |
| ATK Autos Limited | Wholesale & retail | 2024 |
| ATK Self Storage Limited | Transport & logistics | 2022 |
| Atkar Corporation Limited | Real estate | 2024 |
| ATL Homes Ltd | Real estate | 2025 |
| ATL Jones Limited | Wholesale & retail | 2021 |
| Atlanthor Ltd | Health & social care | 2022 |
| Atlantic Drift Ltd | Wholesale & retail | 2019 |
| Atlantic Fire & Security Specialists Limited | Professional & scientific | 2024 |
| Atlantic Fostering Services Ltd | Health & social care | 2024 |
| Atlantic Healthcare Services Limited | Health & social care | 2023 |
| Atlantic Security Ltd | Administrative & support | 2026 |
| Atlantic Solutions Ltd | Real estate | 2017 |
| Atlantica Marketing Ltd | Professional & scientific | 2024 |
| Atlantichse Ltd | Water & waste | 2026 |
| Atlantique Consulting Ltd | Financial services | 2009 |
| Atlantis MIF Ltd | Professional & scientific | 2022 |
| Atlas Advisory Services Ltd | Professional & scientific | 2019 |
| Atlas Brands Limited | Construction | 2023 |
| Atlas GS Limited | Construction | 2024 |
| Atlas Home Support Limited | Health & social care | 2011 |
| Atlas Renovations Ltd | Construction | 2024 |
| Atlas Star UK Ltd | Construction | 2019 |
| Atlas Trade Solutions Limited | Transport & logistics | 2019 |
| Atlas Travel Limited | Administrative & support | 2020 |
| Atlas Travel Solutions Limited | Administrative & support | 2008 |
| Atlas Verity Limited | Education | 2026 |
| Atlasfair Ltd | Manufacturing | 2001 |
| Atlasmere Ltd | Information & communication | 2025 |
| Atls-Ivm Limited | Real estate | 2026 |
| ATM Investment Ltd | Real estate | 2015 |
| ATM Portfolio Investments Ltd | Real estate | 2025 |
| ATM Proper T Ltd | Real estate | 2016 |
| ATM Trading Limited | Wholesale & retail | 2016 |
| Atma Limited | Arts & recreation | 2024 |
| Atman Intelligence Limited | Real estate | 2019 |
| Atmar & Co. Ltd | Other services | 2025 |
| ATN Business Services Limited | Administrative & support | 2020 |
| Atoany Limited | Wholesale & retail | 2024 |
| Atom Aesthetics Limited | Other services | 2023 |
| Atom Shopping Ltd | Wholesale & retail | 2024 |
| Atozremovalandcleaners Limited | Wholesale & retail | 2025 |
| ATP Computing Ltd | Information & communication | 2009 |
| Atpropertville Limited | Real estate | 2025 |
| Atrium Accountants Ltd | Professional & scientific | 2024 |
| Atrium Portfolios Ltd | Real estate | 2019 |
| Atrn Limited | Wholesale & retail | 2021 |
| Atrox London Ltd | Wholesale & retail | 2026 |
| ATS 86 Ltd | Other services | 2018 |
| ATS Atlas Travel Solutions Limited | Administrative & support | 2012 |
| ATS Support Services Limited | Administrative & support | 2019 |
| Atsa Global Limited | Wholesale & retail | 2026 |
| Atta Bazaar Ltd | Wholesale & retail | 2025 |
| Atta Saleem Ltd | Other services | 2024 |
| Attentive Security Ltd | Hospitality | 2020 |
| Attico Limited | Real estate | 2002 |
| Attila EL Ltd | Construction | 2022 |
| Attleborough Convenience Store Ltd | Wholesale & retail | 2021 |
| Attock Cash & Carry Limited | Wholesale & retail | 2025 |
| Attornea Limited | Professional & scientific | 2023 |
| Attract Trade Ltd | Wholesale & retail | 2024 |
| Attratalent Limited | Administrative & support | 2017 |
| ATZ UK Properties Ltd | Real estate | 2024 |
| AU Medics Limited | Health & social care | 2015 |
| AU Motor Group Ltd | Wholesale & retail | 2026 |
| Auckland Global Ltd | Real estate | 2024 |
| Auddin Ltd | Wholesale & retail | 2018 |
| Audentes Ltd | Professional & scientific | 2011 |
| Audiomach Limited | Administrative & support | 2019 |
| Audiomodz Limited | Wholesale & retail | 2018 |
| AUE Construct Ltd | Construction | 2022 |
| Auefix Cladding Ltd | Construction | 2023 |
| Augustino Fruit and VEG Ltd | Wholesale & retail | 2025 |
| Augustswimclub Limited | Real estate | 2025 |
| AUH Traders Ltd | Wholesale & retail | 2023 |
| Aujla Assets Ltd | Real estate | 2025 |
| Aujla Developments Ltd | Administrative & support | 2019 |
| AUM Dhillon Construction Ltd | Construction | 2017 |
| AUM J&T Properties LLP | | 2017 |
| AUM Lettings J&T Limited | Real estate | 2025 |
| AUM Property Management Limited | Real estate | 2017 |
| AUN Abbas Traders Ltd | Wholesale & retail | 2025 |
| Aunix Solutions Limited | Health & social care | 2023 |
| Aunor Brands Ltd | Wholesale & retail | 2024 |
| Aura Accountants Limited | Professional & scientific | 2012 |
| Aura Allure Limited | Wholesale & retail | 2023 |
| Aura Distributions Ltd | Wholesale & retail | 2025 |
| Aura Essex Properties Limited | Real estate | 2019 |
| Aura Hideaway Ltd | Real estate | 2025 |
| Aura House of Perfume Limited | Wholesale & retail | 2023 |
| Aura Invents Ltd | Wholesale & retail | 2024 |
| Aura Kent Properties Limited | Real estate | 2025 |
| Auramart Ltd | Wholesale & retail | 2026 |
| Aurelia Terra Ltd | Real estate | 2026 |
| Aurene by Anupama Ltd | Wholesale & retail | 2026 |
| Aurescent Estates Limited | Real estate | 2025 |