| Assystem Holding UK Limited | Financial services | 2024 |
| AST Prestige Limited | Professional & scientific | 2025 |
| Astemo UK, Ltd. | Manufacturing | 1997 |
| Asten Construction Consultancy Ltd | Professional & scientific | 2025 |
| Asthmatic Limited | Manufacturing | 2008 |
| Astley (1919) Co Ltd | Financial services | 2025 |
| Astley Bridge Building Services Limited | Construction | 2003 |
| Astley Bridge Buses Ltd | Transport & logistics | 2015 |
| Astley Containers and Cabins Limited | Administrative & support | 2017 |
| Astley Electrical Supplies Ltd | Wholesale & retail | 2012 |
| Astley Grange Homes Limited | Health & social care | 2013 |
| Astley Limited | Hospitality | 2023 |
| Aston & Quinn Ltd | Real estate | 2020 |
| Aston Darby Capital Limited | Real estate | 2017 |
| Aston Darby Harbour Property Limited | Real estate | 2017 |
| Aston Darby Limited | Real estate | 2017 |
| Aston MTB Ltd | Information & communication | 2021 |
| Astr Group Ltd | Administrative & support | 2026 |
| Astr Trading Ltd | Administrative & support | 2026 |
| Astra TEC Limited | Administrative & support | 2023 |
| Astra-Tec Solutions Ltd | Wholesale & retail | 2017 |
| Astracam Ltd | Manufacturing | 2022 |
| Astradin Properties Ltd | Real estate | 2020 |
| Astraeus Investments Ltd | Real estate | 2021 |
| Astreos Property Ltd | Real estate | 2025 |
| Astrosec Ltd | Information & communication | 2025 |
| Astrosoc Computing Services Ltd | Information & communication | 2014 |
| Asymptick Limited | Information & communication | 2020 |
| AT & Sons Services and Logistics Ltd | Manufacturing | 2024 |
| AT Convenience Limited | Transport & logistics | 2021 |
| AT Optical Ltd | Health & social care | 2021 |
| AT Ventures Limited | Other services | 2022 |
| ATA Retail Ltd | Wholesale & retail | 2021 |
| Atalaria Ltd | Wholesale & retail | 2018 |
| Atcam Limited | Health & social care | 2013 |
| Atcha Optical Services Limited | Health & social care | 2020 |
| ATE IT Solutions Limited | Information & communication | 2007 |
| Ateeqs Ltd | Wholesale & retail | 2024 |
| Atelier FL Limited | Professional & scientific | 2019 |
| Athalete Ltd | Professional & scientific | 2022 |
| Athan A&V Ltd | Other services | 2024 |
| Athar Ltd | Wholesale & retail | 2023 |
| Athena Data Centres Ltd | Information & communication | 2017 |
| Athena Education Limited | Education | 2015 |
| Atherton Consultancy (North West) Ltd | Financial services | 2011 |
| Atherton Shop Smart Limited | Wholesale & retail | 2012 |
| Athlaz Limited | Information & communication | 2025 |
| Athletic Sports (UK) Ltd | Wholesale & retail | 2010 |
| Atholl Protection Services Ltd | Administrative & support | 2021 |
| Atick Ltd | Transport & logistics | 2026 |
| Atil Property Limited | Real estate | 2024 |
| Atilgan Properties Limited | Real estate | 2021 |
| ATK London Limited | Professional & scientific | 2020 |
| Atkins Analytics Limited | Professional & scientific | 2024 |
| Atkinson & James Interiors Limited | Construction | 2016 |
| ATL International Law Limited | Administrative & support | 2014 |
| ATL Logistic Ltd | Wholesale & retail | 2023 |
| Atlantic Cooling Limited | Manufacturing | 2020 |
| Atlantic Design Print Ltd | Manufacturing | 2023 |
| Atlantic Group (NW) Ltd | Other services | 2022 |
| Atlantic Limousines Ltd | Other services | 2015 |
| Atlantic Prestige Ltd | Administrative & support | 2020 |
| Atlantic Transport Ltd | Transport & logistics | 2016 |
| Atlantic Travel (GB) Limited | Transport & logistics | 2007 |
| Atlantis Electric Limited | Manufacturing | 2019 |
| Atlas Blinds Ltd | Manufacturing | 2022 |
| Atlas Building Solutions Ltd | Construction | 2024 |
| Atlas Designs (NW) Ltd | Construction | 2025 |
| Atlas Electrics Ltd | Construction | 2024 |
| Atlas Ground Works Ltd | Construction | 2024 |
| Atlas Guardrail Limited | Manufacturing | 1996 |
| Atlas Insolvency Ltd | Administrative & support | 2021 |
| Atlas Mill Ltd | Information & communication | 2021 |
| Atlas Minibuses Limited | Transport & logistics | 2018 |
| Atlas Nova Ltd | Administrative & support | 2024 |
| Atlas Plumbing Solutions Ltd | Construction | 2024 |
| Atlas Prime Ltd | Water & waste | 2024 |
| Atlas Travel Agency Ltd | Administrative & support | 2024 |
| Atlconsult Limited | Professional & scientific | 2024 |
| ATM Medical Limited | Health & social care | 2023 |
| Atodra Investments Ltd | Financial services | 2022 |
| Atom Digitalz Ltd | Wholesale & retail | 2023 |
| Atom Electrical NW Ltd | Construction | 2026 |
| Atom Security UK Ltd | Manufacturing | 2015 |
| Atom UK Limited | Information & communication | 2004 |
| Atomic Aromas Ltd | Wholesale & retail | 2025 |
| Atomic Dance Ltd | Education | 2023 |
| Atozi Group Limited | Wholesale & retail | 2021 |
| Atozmedix C.I.C. | Education | 2025 |
| Atra Transport Ltd | Transport & logistics | 2025 |
| Atria Holdings Limited | Professional & scientific | 2011 |
| Atsarmstrong Limited | Transport & logistics | 2018 |
| Attention Seekers Productions Limited | Administrative & support | 2011 |
| Atticus Distribution Ltd | Wholesale & retail | 2023 |
| Attirex Limited | Wholesale & retail | 2023 |
| Attmist Ltd | Professional & scientific | 2023 |
| Attsense Limited | Wholesale & retail | 2022 |
| ATU Project Ltd | Health & social care | 2025 |
| ATW Consultancy Limited | Professional & scientific | 2025 |
| AU & YM Optical Ltd | Health & social care | 2022 |