| Atkins and Co Homes Limited | Real estate | 2022 |
| Atkins Builders Ltd | Construction | 2018 |
| Atkins Heritage Property Limited | Real estate | 2022 |
| Atkinson Parker Refrigeration Ltd | Construction | 2004 |
| ATL & Family Limited | Real estate | 2024 |
| Atlantic Blue Holdings Limited | Financial services | 2019 |
| Atlantic INT. Limited | Wholesale & retail | 2025 |
| Atlantic West Management Limited | Real estate | 2013 |
| Atlas North Holdings Limited | Professional & scientific | 2015 |
| Atlas 2U Ltd | Financial services | 2017 |
| Atlas Commercial Contracting Limited | Construction | 1989 |
| Atlas Development Projects Limited | Construction | 2005 |
| Atlas Finishings Limited | Construction | 2020 |
| Atlas Ground Protection Ltd | Administrative & support | 2025 |
| Atlas Interior Design Ltd | Manufacturing | 2024 |
| Atlas Luxco Ltd | Real estate | 2025 |
| Atlas North Properties Limited | Real estate | 2022 |
| Atlas Quantity Surveying Limited | | 1985 |
| Atlas Refurbishment (Northern) Limited | Construction | 1997 |
| Atlas Structural Design Limited | Professional & scientific | 2025 |
| Atlas Technical Services Limited | Wholesale & retail | 2003 |
| Atlas-Uk Electrical Engineering Ltd | Construction | 2022 |
| Atlasaxis Ltd | Wholesale & retail | 2024 |
| Atmos Recordings Limited | Arts & recreation | 2024 |
| Atobviac Limited | Information & communication | 2003 |
| Atom Detailing Limited | Wholesale & retail | 2019 |
| Atom Electric Services Limited | Construction | 2022 |
| Atom Software Ltd | Information & communication | 2017 |
| Atomhawk Design Ltd | Information & communication | 2009 |
| Atomic 56 Limited | Manufacturing | 2010 |
| Atomic Programming Limited | Manufacturing | 2002 |
| Atomising Systems Limited | Manufacturing | 1992 |
| Atousa Ltd | Manufacturing | 2026 |
| Atoy Venue Ltd | Hospitality | 2021 |
| Atrada Ltd | Water & waste | 2021 |
| Atreus Ltd | Construction | 2022 |
| Atria Maison Properties Ltd | Hospitality | 2026 |
| Atropos Bars Ltd | Hospitality | 2023 |
| Atroposaurus Bar Ltd | Hospitality | 2023 |
| ATS 2000 (UK) Limited | Wholesale & retail | 2019 |
| Atta Food Ltd | Hospitality | 2025 |
| Attercliffe Consultants Limited | Manufacturing | 2017 |
| Attercliffe Gymnastics Academy Limited | Arts & recreation | 2017 |
| Attercliffe Realisations Limited | Transport & logistics | 1952 |
| Attercliffe Spray Booth Limited | Wholesale & retail | 2026 |
| Attercliffe Tyre & Service Centre Limited | Wholesale & retail | 2026 |
| Attercliffestopnshop Ltd | Wholesale & retail | 2020 |
| Atticus SHE Management Limited | Real estate | 2022 |
| Attique 1789 Limited | Public administration | 2020 |
| Attley's Collective Ltd | Hospitality | 2025 |
| Attribute AI LLC Ltd | Wholesale & retail | 2025 |
| Attwood Technical Services Limited | Professional & scientific | 2006 |
| ATW Financial Services Ltd | Financial services | 2020 |
| Atws Estates Ltd | Real estate | 2025 |
| Atwud Engineering Services Ltd | Manufacturing | 2010 |
| ATY Properties Limited | Real estate | 2025 |
| Atys Limited | Administrative & support | 2004 |
| AU Halal Poultry Ltd | Hospitality | 2019 |
| AU Village Ltd | Hospitality | 2026 |
| Aube Lighting Design Ltd | Professional & scientific | 2018 |
| Aubert & Duval UK Ltd | Wholesale & retail | 2023 |
| Auckland Enterprises Ltd | Financial services | 2023 |
| Auckland Investment Properties Ltd | Real estate | 2023 |
| Auction My Property Limited | Real estate | 2006 |
| Audastra Limited | Professional & scientific | 2025 |
| Auddin Trading Ltd | Hospitality | 2022 |
| Audio Engineering and Installation Ltd | Administrative & support | 2022 |
| Audio&Sound Hire Limited | Real estate | 2025 |
| Audiologycqc Limited | Public administration | 2023 |
| Audo Design Limited | Wholesale & retail | 2018 |
| Auger Ophthalmics Ltd | Health & social care | 2021 |
| Aughton Hospitality Limited | Hospitality | 2020 |
| Aughton Motor Services Limited | Real estate | 1960 |
| Augusta Golf Products Ltd | Professional & scientific | 2010 |
| Augustus Property Services Limited | Real estate | 2008 |
| AUK Electronics UK Limited | Wholesale & retail | 2018 |
| Aunstech Limited | Manufacturing | 2024 |
| Auntie Julie's Limited | Hospitality | 2019 |
| Aura Cosmetics and Aesthetics Ltd | Other services | 2015 |
| Aura DE Luxe Ltd | Manufacturing | 2023 |
| Aura Satz Limited | Arts & recreation | 2014 |
| Auravive Energy Ltd | Energy | 2026 |
| Aurazelis Ltd | Wholesale & retail | 2025 |
| Aurelia Arkiva Properties Ltd | Households | 2026 |
| Aurelith Ltd | Wholesale & retail | 2025 |
| Aurevia Nails Ltd | Other services | 2025 |
| Aurexon Technologies Ltd | Construction | 2026 |
| Auric Finance Limited | Financial services | 2026 |
| Auriol (Passfield) Limited | Real estate | 1957 |
| Auron Limited | Extraterritorial | 2003 |
| Aurora (Spring Pressings) Limited | | 1946 |
| Aurora Aicloud Limited | Information & communication | 2025 |
| Aurora Austral Ltd | Public administration | 2022 |
| Aurora Echo Music Ltd | Information & communication | 2025 |
| Aurora Forgings Limited | Professional & scientific | 1966 |
| Aurora Global Properties Ltd | Real estate | 2025 |
| Aurora Industries Ltd | Construction | 2026 |
| Aurora Land Limited | Professional & scientific | 2019 |
| Aurora Peak Ltd | Professional & scientific | 2013 |
| Auroraie Limited | Wholesale & retail | 2025 |