| Atdunn Limited | Agriculture & fishing | 2025 |
| Atfx Training Ltd | | 2015 |
| Athem Music Ltd | Wholesale & retail | 2021 |
| Athera Marketing Limited | Professional & scientific | 2025 |
| Athlon Consulting Ltd | Professional & scientific | 2023 |
| Athlos Global Ltd | Professional & scientific | 2023 |
| Atkins Brothers Ltd | Construction | 2019 |
| Atlantic Union Limited | Wholesale & retail | 2025 |
| Atlantis Renovations Ltd | Construction | 2026 |
| Atlas Asset Holdings Ltd | Real estate | 2024 |
| Atlas Asset Management Ltd | Extraterritorial | 2024 |
| Atlas Capital Holdings Ltd | Financial services | 2025 |
| Atlas Green Services Limited | Professional & scientific | 2026 |
| Atlas Records Limited | Wholesale & retail | 2018 |
| Atlas Scaffolding & Roofing Ltd | Construction | 2024 |
| Atlas Scaffolding South West Ltd | Construction | 2019 |
| Atom Build Ltd | Construction | 2009 |
| Atomic Drywall Limited | Real estate | 2020 |
| Atomic Fashion Marketing UK Limited | Wholesale & retail | 2024 |
| Atwww (UK) Limited | Information & communication | 2000 |
| Auditsure Ltd | Professional & scientific | 2014 |
| Augusta IT Limited | Other services | 2019 |
| Aura EAR Care Ltd | Health & social care | 2026 |
| Aura Events Limited | Professional & scientific | 2003 |
| Aura Jewels Limited | Wholesale & retail | 2003 |
| Aura Mirrors Ltd | Wholesale & retail | 2026 |
| Aura-Uk Ltd | Real estate | 2017 |
| Aurelium Health Ltd | Health & social care | 2020 |
| Aurelius Sight Limited | Financial services | 2024 |
| Authentic Digital Limited | Information & communication | 2012 |
| Auto Car Sale Taunton Ltd | Wholesale & retail | 2025 |
| Auto Car Sales Taunton Ltd | Wholesale & retail | 2023 |
| Auto Care and Repair Ltd | Wholesale & retail | 2019 |
| Auto-Lac Services Ltd | Wholesale & retail | 2018 |
| Autofix Car & Commercial Limited | Wholesale & retail | 2025 |
| Autogleam UK Ltd | Other services | 2009 |
| Automotive Climate Services Ltd | Wholesale & retail | 2025 |
| Automotive Enhancement Services Ltd | Wholesale & retail | 2019 |
| Autonom Ltd | Administrative & support | 2020 |
| Autord Limited | Professional & scientific | 2015 |
| Autos RK Limited | Administrative & support | 2026 |
| AV Dance Magic Ltd | Health & social care | 2019 |
| Avado Concepts Beheer Limited | Administrative & support | 2012 |
| Avado Concepts Limited | Information & communication | 2012 |
| Avalancheworks Ltd | Professional & scientific | 2026 |
| Avalon (Management Company) Limited | Households | 2005 |
| Avalon House (Minehead) Management Company Limited | Households | 2007 |
| Avalon Knife Grinding Ltd | Professional & scientific | 2013 |
| Avalon Medical Services Ltd | Health & social care | 2020 |
| Avalon Motorcycle Training Limited | Education | 2021 |
| Avalon Property Portfolios Limited | Real estate | 2024 |
| Avalon Waste Management Limited | Water & waste | 2010 |
| Avalon Wholesale and Brewing Limited | Wholesale & retail | 2015 |
| Avant Properties Limited | Construction | 2007 |
| Avantis Protection Group Ltd | Administrative & support | 2025 |
| Avenquor Ltd | Wholesale & retail | 2026 |
| Avery Carpentry Contractors Limited | Construction | 2008 |
| Avery Contractors Limited | Construction | 2014 |
| Aviation & Marine (Services) Limited | Professional & scientific | 2013 |
| Avingmen Limited | Professional & scientific | 1988 |
| Avis & Doyle Ltd | Construction | 2012 |
| Avis Agri Ltd | Agriculture & fishing | 2026 |
| AVO Property Limited | Real estate | 2021 |
| Avocado Digs Ltd | Real estate | 2022 |
| Avocet Medical Limited | Health & social care | 2022 |
| Avondale Painting and Decorating Limited | Construction | 2013 |
| Avonn Dale Ltd | Real estate | 2021 |
| Avrd Real Estate Ltd | Real estate | 2026 |
| AVS Southwest Ltd | Construction | 2019 |
| Awan UK Trading Ltd | Wholesale & retail | 2024 |
| Award Group Limited | Construction | 2020 |
| Aware Services Limited | Information & communication | 2000 |
| AWP Services Limited | Manufacturing | 2007 |
| AX Advocaten LLP | | 2015 |
| Axiom Education Ltd | Education | 2023 |
| Axiom Growth Group Ltd | Professional & scientific | 2026 |
| Axivio Ltd | Real estate | 2020 |
| Axolotl Trading Ltd | Professional & scientific | 2017 |
| Aycicek Ltd | Hospitality | 2014 |
| Ayesha Aslam Limited | Wholesale & retail | 2026 |
| Ayres to There Ltd | Transport & logistics | 2015 |
| Aytt Ltd | Health & social care | 2015 |
| AZ World Digital Marketing & Services Ltd | Wholesale & retail | 2025 |
| Azimuth Fields Ltd | Professional & scientific | 2015 |
| B & H Lettings Ltd | Real estate | 2017 |
| B and M Global Security Services Limited | Administrative & support | 2025 |
| B and W Feeds (Mobile) Limited | Agriculture & fishing | 1998 |
| B B Wear Limited | Wholesale & retail | 2011 |
| B Cole Electrical Limited | Construction | 2024 |
| B Coles SW Ltd | Financial services | 2019 |
| B Collier Property Ltd | Real estate | 2023 |
| B J Property Developments Limited | Real estate | 2003 |
| B L Foxwell Limited | Agriculture & fishing | 2003 |
| B M Coombes & Sons Limited | Agriculture & fishing | 2010 |
| B Perham Consultancy Ltd | Professional & scientific | 2026 |
| B Smart Vehicle Repairs Ltd | Manufacturing | 2019 |
| B&C Williams Management Limited | Professional & scientific | 2025 |
| B. Walsh & Sons Limited | Construction | 1997 |
| B.I.C.F. Limited | Households | 1997 |
| B.J.P. Taping & Jointing Limited | Construction | 2004 |