| Astract Ltd | Financial services | 2025 |
| Astralpool UK Limited | Wholesale & retail | 1984 |
| Astrivon Group Limited | Real estate | 2025 |
| Astro Burgers Ltd | Hospitality | 2024 |
| Astro Creations Ltd | Manufacturing | 2024 |
| AT Jones Holdings Limited | Construction | 2005 |
| ATC Travel Limited | Transport & logistics | 2026 |
| Atelier 33 Architecture Ltd | Professional & scientific | 2023 |
| Athebe Consultancy Limited | Professional & scientific | 2019 |
| Athena Aesthetics Skin Care Clinic Limited | Health & social care | 2021 |
| Athena P2 Ltd | Professional & scientific | 2018 |
| Athene Design Limited | Professional & scientific | 2003 |
| Atitlan Studios Ltd | Manufacturing | 2020 |
| ATJ Facades Limited | Construction | 2016 |
| ATJ People Limited | Education | 2023 |
| ATJ Plant Ltd | Construction | 2016 |
| Atkin Auto Spray Ltd | Construction | 2026 |
| Atlantic Regeneration 1 Nominee 1 Limited | Financial services | 2012 |
| Atlantic Regeneration 1 Nominee 2 Limited | Financial services | 2012 |
| Atlantic Regeneration 1 Security Agent Limited | Financial services | 2012 |
| Atlantic Regeneration Property 1 General Partner Limited | Financial services | 2012 |
| Atlantic Regeneration Property 1 Limited Partnership | | 2012 |
| Atlantic Valentino Limited | Wholesale & retail | 2017 |
| Atlas Green Energy Limited | Energy | 2021 |
| Atlas Language and Media Ltd | Wholesale & retail | 2023 |
| Atlas Mobility Conversions Ltd | Manufacturing | 2013 |
| Atlas UK Bidco I Limited | Financial services | 2026 |
| Atlas UK Midco I Limited | Financial services | 2026 |
| Atlas UK Topco I Limited | Financial services | 2025 |
| Atmk Ltd | Hospitality | 2023 |
| Atmos Medical Limited | Wholesale & retail | 1998 |
| Atrangi Ltd | Manufacturing | 2022 |
| ATS Services and Solutions Ltd | Administrative & support | 2017 |
| Attentive Recruitment Ltd | Administrative & support | 2025 |
| Attiretrends Limited | Wholesale & retail | 2025 |
| Attuned Care Ltd | Health & social care | 2025 |
| Audio Resurgence Ltd | Manufacturing | 2025 |
| Audrée Rose Ltd | Wholesale & retail | 2025 |
| Augmented Solutions Limited | Professional & scientific | 2017 |
| Auilox Limited | Administrative & support | 2018 |
| Aura Beauty & Aesthetics Whiteley Ltd | Other services | 2025 |
| Aura Strategic Developments Ltd | Construction | 2025 |
| Aurivox Ltd | Wholesale & retail | 2026 |
| Aurix Motors Ltd | Wholesale & retail | 2026 |
| Aurora the Awakening Ltd | Wholesale & retail | 2024 |
| Aurum Care Group Limited | Administrative & support | 2025 |
| Auscrew Holdings Limited | Financial services | 2018 |
| Auscrew Limited | Other services | 1993 |
| Autek CIC | Information & communication | 2020 |
| Authorized Access Systems Limited | Administrative & support | 2012 |
| Auto Precision Services Limited | Professional & scientific | 2023 |
| Auto Transport Solutions 2 Ltd | Wholesale & retail | 2022 |
| Auto Tyre Centre Limited | Wholesale & retail | 1994 |
| Automated Cutting Solutions Limited | Manufacturing | 1988 |
| Automotive Engineering Technologies UK Limited | Energy | 2008 |
| Auyaiojsubp Limited | Wholesale & retail | 2025 |
| Av'Alook Studios Ltd | Administrative & support | 2025 |
| Avaantony Limited | Manufacturing | 2025 |
| Avalanche Electronic Solutions Limited | Manufacturing | 2014 |
| Avalerion UK Ltd | Professional & scientific | 2016 |
| Avamax Group Limited | Financial services | 2024 |
| Avant Gardener Ltd | Administrative & support | 2022 |
| Avanti Associates (UK) Limited | Professional & scientific | 2014 |
| Aveli Consulting Limited | Professional & scientific | 2026 |
| Avenue Business Services Limited | Professional & scientific | 2000 |
| Aviation Innovations Limited | Information & communication | 2019 |
| Avon GAS Elecs Limited | Professional & scientific | 2020 |
| AW & Co Properties Ltd | Real estate | 2021 |
| AW Flow Holdings Limited | Extraterritorial | 2010 |
| AW Security Limited | Real estate | 2020 |
| AW Tattoo Limited | Health & social care | 2021 |
| Awakening Fertility Ltd | Other services | 2015 |
| Awakening Sovereignty Limited | Health & social care | 2026 |
| Award Plumbing Limited | Construction | 2023 |
| AWD Legal Services Limited | Professional & scientific | 2019 |
| AWE by the Lake Limited | Health & social care | 2025 |
| Awesome Wilson Associates Limited | Professional & scientific | 2011 |
| Awgreen Energy Limited | Professional & scientific | 2026 |
| AXC Consulting Ltd | Professional & scientific | 2025 |
| Axiogrow Ltd | Information & communication | 2019 |
| Axios Bidco Limited | Financial services | 2015 |
| Ayesha Health Solutions Limited | Administrative & support | 2025 |
| Ayewa Aberfur Limited | Wholesale & retail | 2014 |
| Aylesbury Gatehouse Specsavers Limited | Wholesale & retail | 2023 |
| Aylesbury Specsavers Hearcare Limited | Wholesale & retail | 2006 |
| Aylesbury Specsavers Limited | Wholesale & retail | 2001 |
| Aylesbury Visionplus Limited | Wholesale & retail | 2000 |
| AYR Specsavers Hearcare Limited | Wholesale & retail | 2014 |
| AYR Specsavers Limited | Wholesale & retail | 1993 |
| AYR Visionplus Limited | Wholesale & retail | 1993 |
| Aztec Financial Services (UK) Limited | Financial services | 2006 |
| Aztec UK Europe Holdings Limited | Financial services | 2024 |
| Azteca Football Ltd | Information & communication | 2020 |
| Azteca Limited | Real estate | 2006 |
| Azzurro Associates Holdings LLP | | 2017 |
| Azzurro Associates Limited | Financial services | 2017 |
| B & D Hygiene Systems Ltd | Administrative & support | 2012 |
| B & G Associates (Southampton) Limited | Real estate | 1994 |
| B & L South Limited | Construction | 2015 |
| B & M Clark (Builders) Limited | Construction | 1978 |