| Astute Property Group Ltd | Real estate | 2024 |
| Astute Strategy Limited | Professional & scientific | 2015 |
| Asureq Limited | Construction | 2013 |
| Asureq Plant Hire Ltd | Administrative & support | 2019 |
| ASV Digital Ltd | Information & communication | 2023 |
| ASV Research Limited | Professional & scientific | 2016 |
| ASW Legal Limited | Professional & scientific | 2018 |
| ASY Legacy Development Ltd | Real estate | 2024 |
| Asya Commercial Kitchen Ltd | Manufacturing | 2024 |
| Asya One Ltd | Real estate | 2023 |
| Asylum Link Merseyside | Health & social care | 2002 |
| Asystant Ltd | Administrative & support | 2026 |
| AT Cost Wholesale Limited | Administrative & support | 2017 |
| AT England Ltd | Wholesale & retail | 2022 |
| AT Fortune Limited | Real estate | 2024 |
| AT Home With Amilalah Ltd | Health & social care | 2025 |
| AT Jain Ltd | Health & social care | 2022 |
| AT the Gate Ltd | Wholesale & retail | 2021 |
| AT Your Convenience (North West) Ltd | Wholesale & retail | 2026 |
| AT2 Ltd | Real estate | 2024 |
| AT2 Property Services Ltd | Professional & scientific | 2025 |
| ATA Medical Limited | Health & social care | 2020 |
| Ataifit Limited | Arts & recreation | 2024 |
| Ataxia North West Support Group CIC | Health & social care | 2019 |
| ATB Electrical Systems Ltd | Construction | 2009 |
| ATB Premier Travel Limited | Transport & logistics | 2025 |
| ATC Engineering Solutions Ltd | Professional & scientific | 2020 |
| Atct Trading Limited | Wholesale & retail | 2024 |
| Atelier Saint Clare Limited | Manufacturing | 2017 |
| Atelier Wealth Ltd | Financial services | 2023 |
| Atenas Financial Services Limited | Financial services | 2024 |
| Atex Estates Ltd | Real estate | 2024 |
| ATH Construction & Management Services Ltd | Construction | 2022 |
| ATH Trading Limited | Administrative & support | 2020 |
| Athana Ltd | Wholesale & retail | 2023 |
| Athea Travel Ltd | Administrative & support | 2021 |
| Athena Building Services Limited | Construction | 2021 |
| Athena Training & Consultancy Ltd | Professional & scientific | 2022 |
| Athena's Fast Food Ltd | Hospitality | 2025 |
| Athena's Greek Food Ltd | Hospitality | 2026 |
| Atheno Limited | Professional & scientific | 2023 |
| Atherton Elecgas Services Ltd | Construction | 2021 |
| Atherton House Group Ltd | Education | 2019 |
| Atherton House Nursery Limited | Education | 2003 |
| Atherton House School Ltd | Education | 2015 |
| Atherton Property Ltd | Construction | 2013 |
| Athi Aaran Limited | Wholesale & retail | 2026 |
| Athina Parfums Ltd | Wholesale & retail | 2024 |
| Athitheeran Ltd | Hospitality | 2025 |
| Athryl Ltd | Information & communication | 2025 |
| Atia Active Limited | Wholesale & retail | 2023 |
| Atinga UK Productions Limited | Manufacturing | 2022 |
| Ation Builders Ltd | Construction | 2026 |
| Atkin Fire & Security Ltd | Construction | 2025 |
| Atkins Ecology Ltd | Professional & scientific | 2015 |
| Atkinson Randell Limited | Professional & scientific | 2023 |
| ATLANTA2495 Ltd | Transport & logistics | 2018 |
| Atlantic Developments N.W Ltd | Households | 2019 |
| Atlantic Electrical Northwest Limited | Construction | 2008 |
| Atlantic Estates (NW) Ltd | Construction | 2007 |
| Atlantic Fire & Security Ltd | Extraterritorial | 2010 |
| Atlantic Group Services Limited | Financial services | 2022 |
| Atlantic Investments Holdings Limited | Financial services | 2023 |
| Atlantic Maintenance Ltd | Construction | 2015 |
| Atlantic Mechanical Services Limited | Construction | 2021 |
| Atlantic Pavillion Limited | Real estate | 2024 |
| Atlantic Property North West Limited | Real estate | 2026 |
| Atlantic Security Solutions Ltd | Administrative & support | 2022 |
| Atlantic Tiling Ltd | Construction | 2015 |
| Atlantic Towers Developments Limited | Construction | 2014 |
| Atlantis Horsham Ltd | Real estate | 2024 |
| Atlantis Plumbing Services UK Limited | Construction | 2021 |
| Atlas & Baray Ltd | Wholesale & retail | 2026 |
| Atlas Asbestos Ltd | Water & waste | 2025 |
| Atlas Construction and Developments Ltd | Construction | 2025 |
| Atlas Damp Proofing UK Limited | Construction | 2024 |
| Atlas Drainage and Groundwork Solutions Ltd | Water & waste | 2024 |
| Atlas Energy Solutions Limited | Energy | 2025 |
| Atlas Estate Agents Limited | Real estate | 2013 |
| Atlas Four Ltd | Wholesale & retail | 2020 |
| Atlas Group Consulting Ltd | Professional & scientific | 2023 |
| Atlas Holiday Homes Limited | Water & waste | 1973 |
| Atlas Hunt’S Cross Ltd | Hospitality | 2026 |
| Atlas Land and Building Limited | Real estate | 2019 |
| Atlas NG Ltd | Hospitality | 2026 |
| Atlas Old Swan Ltd | Hospitality | 2026 |
| Atlas Packaging Limited | Extraterritorial | 1983 |
| Atlas Pharma Co. Limited | Professional & scientific | 2000 |
| Atlas Picks Limited | Wholesale & retail | 2025 |
| Atlas Plumbing & Heating Limited | Construction | 2016 |
| Atlas Preservation Ltd | Construction | 2010 |
| Atlas Sheds Limited | Manufacturing | 1987 |
| Atlascargo Ltd | Transport & logistics | 2025 |
| Atlasgate Trading Limited | Wholesale & retail | 2026 |
| Atlasus Ltd | Construction | 2026 |
| ATM & Co UK Ltd | Administrative & support | 2018 |
| ATM Building Contractors Limited | Construction | 2014 |
| ATM Property Services Limited | Other services | 2015 |
| Atmore Centres Limited | Real estate | 1998 |
| Atmore Investments Limited | Real estate | 1989 |