| ATA Estates (Staverton) LLP | | 2016 |
| ATA Estates (Stoke Fleming) LLP | | 2015 |
| ATA Estates LLP | | 2010 |
| Atana Security Ltd | Administrative & support | 2022 |
| Atanza Ltd | Professional & scientific | 2013 |
| Ataood Investments Limited | Real estate | 2024 |
| Atapattu & Sons UK Limited | Wholesale & retail | 2017 |
| Ataraxia Advisory Limited | Administrative & support | 2017 |
| Ataraxia Ventures Ltd | Administrative & support | 2018 |
| Atarya Ltd | Professional & scientific | 2025 |
| Atava Limited | Education | 2013 |
| ATC Engineering Global Ltd | Professional & scientific | 2025 |
| ATC GAS Ltd | Construction | 2022 |
| Ateel UK Limited | Administrative & support | 2017 |
| Atelier ADA Ltd. | Professional & scientific | 2011 |
| Atelier Holzbauer Ltd | Wholesale & retail | 2018 |
| Atelier Neorah Limited | Wholesale & retail | 2020 |
| Atelier Vandenberghe Group Ltd | Manufacturing | 2021 |
| Ateliers Consulting Ltd | Professional & scientific | 2015 |
| Atharv International Ltd | Information & communication | 2023 |
| Athem Pharma Limited | Wholesale & retail | 2017 |
| Athena A.A. Investments Limited | Health & social care | 2019 |
| Athena Analysts Limited | Information & communication | 2020 |
| Athena Content Limited | Information & communication | 2017 |
| Athenaeum Productions Ltd. | Arts & recreation | 2017 |
| Athir Express Ltd | Transport & logistics | 2018 |
| Athletic Endeavour Ltd | Professional & scientific | 2021 |
| Athos Construction Ltd | Construction | 2015 |
| Atic-Uk Limited | Information & communication | 2000 |
| Atilio Solutions Limited | Information & communication | 2015 |
| Atinus Limited | Professional & scientific | 2003 |
| Ativas Medical Ltd | Health & social care | 2022 |
| ATJ Construction Ltd | Construction | 2020 |
| Atkinson Media Ltd | Information & communication | 2015 |
| Atko Sports Limited | Professional & scientific | 2026 |
| ATL Housing Solutions Ltd | Real estate | 2025 |
| Atlantes Solicitors Limited | Professional & scientific | 2020 |
| Atlantic Blue Products Limited | Other services | 2014 |
| Atlantic Chemicals Trading UK Ltd | Wholesale & retail | 2003 |
| Atlantic Global Shipping Ltd | Professional & scientific | 2021 |
| Atlantic Meridean Company Limited | Administrative & support | 2001 |
| Atlantico Grocery Limited | Wholesale & retail | 2025 |
| Atlantis Construct Ltd | Construction | 2020 |
| Atlantis Properties Ltd | Real estate | 2017 |
| Atlas and Steep Limited | Wholesale & retail | 2026 |
| Atlas Care Homes Group Ltd | Construction | 2024 |
| Atlas Children's Homes Limited | Real estate | 2023 |
| Atlas COE Limited | Construction | 2010 |
| Atlas Dental Group Ltd | Health & social care | 2026 |
| Atlas Drives & Patios Ltd | Administrative & support | 2017 |
| Atlas Global Trading Ltd | Wholesale & retail | 2019 |
| Atlas Lifestyle Consulting Limited | Professional & scientific | 2018 |
| Atlas Longevity Ltd | Wholesale & retail | 2026 |
| Atlas Metal Industries UK Ltd | Wholesale & retail | 2024 |
| Atlas Plus Ltd | Education | 2018 |
| Atlas Vision Limited | Health & social care | 2022 |
| Atlasor Ltd | Other services | 2024 |
| Atlip House Limited | Construction | 2000 |
| ATM (North East) Limited | Hospitality | 2018 |
| ATM Motors Limited | Wholesale & retail | 2025 |
| Atma Estates Limited | Wholesale & retail | 2021 |
| Atmiya Ltd | Health & social care | 2014 |
| Atmr Partners Ltd | Real estate | 2025 |
| ATN Groundworks and Formwork Limited | Construction | 2023 |
| Atomxdigital Ltd | Information & communication | 2018 |
| Atomy Global Care Synergy Centre Ltd | Wholesale & retail | 2025 |
| Atoz Marketplace Limited | Wholesale & retail | 2024 |
| Atoz Shine Cleaning Ltd | Administrative & support | 2025 |
| ATP Pharma Limited | Wholesale & retail | 2026 |
| Atriputra Ltd | Real estate | 2022 |
| ATS Builders Limited | Construction | 2022 |
| ATS Painting Ltd | Construction | 2024 |
| Attarvillage Limited | Wholesale & retail | 2025 |
| Attiro Ltd | Wholesale & retail | 2025 |
| Atul's Kitchen Limited | Professional & scientific | 2009 |
| ATY Construction Ltd | Construction | 2019 |
| Atyourtime Group Limited | Financial services | 2020 |
| Atyourtime Secured Food Delivery Limited | Other services | 2018 |
| Atyourtime Technology Limited | Information & communication | 2019 |
| Atypic AM Holding Ltd | Financial services | 2021 |
| Atypic Skincare Ltd | Manufacturing | 2016 |
| ATZ Property Services Limited | Real estate | 2021 |
| AU Bespoke Limited | Wholesale & retail | 2013 |
| AU Gems & Jewels Ltd | Wholesale & retail | 2024 |
| Audel Healthcare Limited | Administrative & support | 2024 |
| Audel Residences Limited | Health & social care | 2025 |
| Audel Tiney Home Nursery Ltd | Education | 2025 |
| Audell Limited | Real estate | 2020 |
| Audi VW Accident Repair Ltd | Wholesale & retail | 2016 |
| Audi VW Specialist Centre Ltd | Wholesale & retail | 2012 |
| Audio Technology Ltd | Wholesale & retail | 2017 |
| Audiosweep Ltd | Information & communication | 2023 |
| Audley Construction Group Limited | Financial services | 2020 |
| Audley Construction Services Limited | Construction | 2020 |
| Audley Modular International Limited | Construction | 2025 |
| Audley One Ltd | Real estate | 2018 |
| Audley Square Holdings Limited | Financial services | 2018 |
| Audley Square Management Ltd | Real estate | 2016 |
| Audley Square Properties Ltd | Construction | 2011 |
| Audrey & Emily Holdings Ltd | Professional & scientific | 2021 |