| Atlascaf Ltd | Wholesale & retail | 2023 |
| Atlasprime Logistics Ltd | Transport & logistics | 2025 |
| Atlasun Ltd | Manufacturing | 2024 |
| ATM ENT UK Ltd | Hospitality | 2022 |
| ATM Foods Supplier Ltd | Hospitality | 2025 |
| ATM Properties Services Ltd | Real estate | 2020 |
| Atman Eternal Limited | Financial services | 2019 |
| Atmos Hospitality Group Ltd | Hospitality | 2026 |
| Atmos Restaurant Ltd | Hospitality | 2025 |
| Atmosphere Media Ltd | Professional & scientific | 2025 |
| Atmospheric Empire Ltd | Professional & scientific | 2023 |
| Atmospherical Limited | Extraterritorial | 2016 |
| Atmz Ventures Ltd | Health & social care | 2026 |
| ATN Services and Products Limited | Wholesale & retail | 2011 |
| Atnaik Consult Ltd | Information & communication | 2022 |
| Atnjs Limited | Real estate | 2026 |
| Atnn Ltd | Real estate | 2025 |
| Atom Cleaners Ltd | Administrative & support | 2019 |
| Atom Jewellery Limited | Manufacturing | 1986 |
| Atone Global Ltd | Real estate | 2025 |
| Atonement Clothing Limited | Wholesale & retail | 2018 |
| Atora Ltd | Manufacturing | 2013 |
| Atos Group Limited | Construction | 2022 |
| Atos Security Services Ltd | Administrative & support | 2025 |
| Atoz Advertising Ltd | Information & communication | 2012 |
| Atoz Housing Solutions Ltd | Real estate | 2025 |
| Atoz Removals and Deliveries Ltd | Transport & logistics | 2026 |
| Atoz System Ltd | Wholesale & retail | 2023 |
| ATR Property Management Ltd | Construction | 2018 |
| Atreya Ltd | Health & social care | 2014 |
| Atrio Property Ltd | Real estate | 2016 |
| Atruchecks Ltd | Health & social care | 2019 |
| Atrumed Ltd | Other services | 2017 |
| ATS Cleaning Solutions Ltd | Administrative & support | 2026 |
| ATS Euromaster Limited | Wholesale & retail | 2001 |
| ATS Medical Consultancy Limited | Health & social care | 2012 |
| ATS Property and Real Estate Limited | Real estate | 2019 |
| ATS Tech Solutions Limited | Information & communication | 2018 |
| ATS UK Holdings Ltd | Administrative & support | 2022 |
| Atta Convenience Store Ltd | Wholesale & retail | 2026 |
| Atta Khan Limited | Health & social care | 2022 |
| Atta Rehman Limited | Wholesale & retail | 2026 |
| Atta Solutions Ltd | Information & communication | 2025 |
| Atta-Gul Holdings Limited | Hospitality | 2023 |
| Attain Fleet Services Limited | Administrative & support | 2001 |
| Attain Travel Limited | Transport & logistics | 1995 |
| Attakon Limited | Financial services | 2025 |
| Attalqeen Limited | Education | 2025 |
| ATTARI11 Ltd | Real estate | 2015 |
| Attay Ltd | Wholesale & retail | 2024 |
| Attease Construction & Property Management Ltd | Construction | 2010 |
| Attelas Consulting Limited | Professional & scientific | 2016 |
| Attelas Ltd | Professional & scientific | 2016 |
| Attend Impex LP | | 2014 |
| Attentive Home Care Ltd | Health & social care | 2024 |
| Attentive Housing Ltd | Real estate | 2021 |
| Attentive Mobile UK Ltd | Information & communication | 2021 |
| Attergirl Productions Ltd | Information & communication | 2025 |
| Attibo Ltd | Real estate | 2019 |
| Atticus Consulting Limited | Administrative & support | 2015 |
| Atticus Logistics Limited | Transport & logistics | 2014 |
| Attif Time Ltd | Professional & scientific | 2025 |
| Attingham Drive 20-30 RTM Company Limited | Households | 2024 |
| Attingham Drive Management Company Limited | Households | 2013 |
| Attire by ANU Ltd | Wholesale & retail | 2025 |
| Attire Corner Limited | Wholesale & retail | 2025 |
| Attire Emea Ltd | Manufacturing | 2012 |
| Attire Holdings Ltd | Extraterritorial | 2021 |
| Attireaura Ltd | Wholesale & retail | 2025 |
| Attired Online Ltd | Wholesale & retail | 2022 |
| Attlas Commercial Finance Limited | Financial services | 2026 |
| Attock Buffet Ltd | Hospitality | 2026 |
| Attock Construction Ltd | Construction | 2024 |
| Attock LPG Ltd | Wholesale & retail | 2025 |
| Attock Property Ltd | Real estate | 2023 |
| Attock Roti Junction Ltd | Hospitality | 2022 |
| Attokyo Ltd | Hospitality | 2025 |
| Attorney Wills Limited | Administrative & support | 2018 |
| Attraction World Group Limited | Financial services | 2020 |
| Attraction World Holdings Limited | Financial services | 2010 |
| Attraction World Limited | Administrative & support | 2005 |
| Attraction World Ventures Limited | Financial services | 2020 |
| Attwood Estates Ltd | Real estate | 2009 |
| Atune Remaps Ltd | Wholesale & retail | 2025 |
| Atwal (Midlands) Limited | Hospitality | 2018 |
| Atwal's Holdings Ltd | Financial services | 2026 |
| Atwamonpoat Limited | Wholesale & retail | 2021 |
| Atypical Butterfly Affect Ltd | Wholesale & retail | 2023 |
| AU & AJ Ltd | Wholesale & retail | 2024 |
| AU 25 Ltd | Hospitality | 2026 |
| AU Construction Ltd | Construction | 2026 |
| AU Creative Ltd | Manufacturing | 2017 |
| AU Enterprise Ltd | Wholesale & retail | 2019 |
| AU Gadget Zone Limited | Wholesale & retail | 2025 |
| AU6 Limited | Hospitality | 2023 |
| Auaa Ltd | Real estate | 2018 |
| Aube Property Holdings Limited | Real estate | 2014 |
| Aubrey Motor Company Ltd | Wholesale & retail | 2016 |
| Aubrey T P W Limited | Wholesale & retail | 2022 |
| Auckland 1966 Limited | Extraterritorial | 2013 |