| Aspire Shop Ltd | Wholesale & retail | 2026 |
| Aspire Wellbeing Limited | Financial services | 2019 |
| Aspire West Yorkshire Limited | Real estate | 2022 |
| Aspire Young Persons Connect Limited | Health & social care | 2017 |
| Aspirex NE Ltd | Professional & scientific | 2025 |
| Aspiria Motors Limited | Manufacturing | 2025 |
| Aspirito Holdings Limited | Financial services | 2025 |
| Asra Property Group Limited | Real estate | 2017 |
| Asra Property Holdings Limited | Real estate | 2021 |
| Asset Fire Protection Ltd. | Construction | 2020 |
| Asset Investments & Management Limited | Real estate | 2025 |
| Asset LET and Stay Limited | Real estate | 2024 |
| Asset Manager Solutions Limited | Hospitality | 2006 |
| Asset Manager Solutions TM Limited | Hospitality | 2015 |
| Assets Renovation Limited | Construction | 2021 |
| Assist MI Ltd | Information & communication | 2010 |
| Associated Educational Technologies Ltd | Information & communication | 2014 |
| Association for Curators and Programmers of Asian Cinemas CIC | Other services | 2025 |
| Association of Certified International Accountants(The) | Professional & scientific | 1985 |
| Association of Dental Groups | Administrative & support | 2011 |
| Association of Education Advisers | Education | 2018 |
| Association of International Accountants(The) | Other services | 1932 |
| Association of International Certified Public Accountants | Other services | 2004 |
| Association of International Financial Accountants | Other services | 2007 |
| Association of Practising and Commercial Accountants Limited(The) | Professional & scientific | 1945 |
| Assure Aesthetics Ltd | Other services | 2022 |
| Assureops Ltd | Information & communication | 2026 |
| Astera Tiles Ltd | Construction | 2024 |
| Astley Pizza Ltd | Hospitality | 2023 |
| Aston Bourne Brighton Limited | Wholesale & retail | 2014 |
| Aston Park Education Consulting Limited | Information & communication | 2015 |
| Astonwild Limited | Real estate | 2018 |
| Astrad Group Ltd | Other services | 2023 |
| Astral Bloom Limited | Manufacturing | 2026 |
| Astrollogy Limited | Wholesale & retail | 2023 |
| Asuma Ltd | Wholesale & retail | 2024 |
| Asumen-Odle Management Ltd | Professional & scientific | 2026 |
| AT Group Enterprises Limited | Wholesale & retail | 2021 |
| AT Home Limited | Real estate | 2016 |
| AT Home North East Ltd | Health & social care | 2023 |
| AT Management Contracts Ltd | Construction | 2022 |
| AT Precision Ltd | Manufacturing | 2019 |
| AT Travel Services Ltd | Transport & logistics | 2020 |
| AT Utilites Ltd | Energy | 2023 |
| At&Kt Properties Ltd | Real estate | 2024 |
| Atac Property Ltd | Real estate | 2025 |
| ATC Training Limited | Education | 2020 |
| Atelier IAD Ltd | Professional & scientific | 2015 |
| ATH Property Group Ltd | Real estate | 2026 |
| Athena 39 Ltd | Real estate | 2022 |
| Athena Marine Supplies Ltd | Wholesale & retail | 2026 |
| Athena Supreme Ltd | Hospitality | 2018 |
| Athenaeum Developments Limited | Real estate | 1985 |
| Athenaeum Press Limited | Manufacturing | 1986 |
| Athreya Deepthi Limited | Information & communication | 2017 |
| Atkinson-Reader Healthcare Limited | Health & social care | 2025 |
| Atlantic Fork Lifts Limited | Manufacturing | 1998 |
| Atlantic Metropolitan (U.K.) Limited | Real estate | 1982 |
| Atlantic Subsea Ltd | Professional & scientific | 2021 |
| Atlantis Management LLP | | 2005 |
| Atlantis Medicare (Bridgeness) Limited | Health & social care | 2010 |
| Atlantis Medicare (Edinburgh) Limited | Other services | 2010 |
| Atlantis Offshore Limited | Professional & scientific | 2014 |
| Atlas Care Homes Limited | Health & social care | 2014 |
| Atlas Care Management Ltd | Professional & scientific | 2015 |
| Atlas Cloud Limited | Information & communication | 2010 |
| Atlas Hseq Ltd | Professional & scientific | 2026 |
| Atlas Representation Ltd | Professional & scientific | 2026 |
| Atlas Welding & Engineering Supplies Limited | Wholesale & retail | 2012 |
| Atlasbiomics Ltd | Information & communication | 2024 |
| ATM Living Ltd | Wholesale & retail | 2023 |
| Atmc Properties Ltd | Real estate | 2024 |
| ATO Newcastle Ltd | Hospitality | 2024 |
| Atom Bank PLC | Financial services | 2013 |
| Atom EBT Ltd | Professional & scientific | 2016 |
| Atom Holdco PLC | Financial services | 2022 |
| Atom Technology Solutions Limited | Information & communication | 2021 |
| Atomic International Ltd | Professional & scientific | 2018 |
| Atreo Labs Ltd | Information & communication | 2026 |
| Atri Group Ltd | Construction | 2025 |
| ATS Properties Letting and Management Limited | Real estate | 2018 |
| ATS Realisations Limited | Wholesale & retail | 1985 |
| ATS Roofing Limited | Construction | 2012 |
| Attack Music Publishing Limited | Information & communication | 2000 |
| Attain Learning Solutions Limited | Other services | 2015 |
| Attandax Ltd | Information & communication | 2015 |
| Attica Partners LP | | 2017 |
| Attifin AI Ltd | Information & communication | 2025 |
| Attila Books Ltd | Information & communication | 2025 |
| Attire Silks Limited | Wholesale & retail | 2025 |
| ATV Network Limited | Information & communication | 2006 |
| ATW Legal Ltd | Professional & scientific | 2025 |
| Aubo Media Limited | Information & communication | 2024 |
| Auca Technology Ltd | Administrative & support | 2022 |
| Auctionworks Ltd | Real estate | 2025 |
| Auctorus Ltd | Information & communication | 2025 |
| Audio Content Fund | Other services | 2018 |
| Audio Visual Industries Ltd | Construction | 2011 |
| AUDIO4VISUAL Limited | Information & communication | 2008 |
| AUDIT9 Limited | Information & communication | 2012 |