| Attwoods Holdings Limited | Professional & scientific | 1989 |
| Attwoods Limited | Financial services | 1939 |
| Atty Group Ltd | Financial services | 2025 |
| Audere Pure Limited | Manufacturing | 2026 |
| Audience Flow Ltd | Professional & scientific | 2023 |
| Audio Kandi Limited | Information & communication | 2006 |
| Audio Venue Limited | Wholesale & retail | 1997 |
| Audio Visual Berkshire Ltd | Professional & scientific | 2019 |
| Audiophile Limited | Arts & recreation | 2003 |
| Audubon Limited | Administrative & support | 2010 |
| Augerson Consulting Ltd | Professional & scientific | 2026 |
| Austin Knight Ltd | Professional & scientific | 2004 |
| Australand Services Ltd | Information & communication | 2025 |
| Auto Asylum Limited | Wholesale & retail | 2002 |
| Auto Door Direct Limited | Wholesale & retail | 2010 |
| Auto Shine Maidenhead Ltd | Administrative & support | 2025 |
| Autoboost Detailing Limited | Wholesale & retail | 2022 |
| Autofacts Limited | Professional & scientific | 2024 |
| Automobile Repair Centre Limited | Wholesale & retail | 2010 |
| Automotive Online-Parts.Co.Uk Ltd | Wholesale & retail | 2012 |
| Autoshine & More Ltd | Other services | 2021 |
| Autotech ARC Ltd | Wholesale & retail | 2006 |
| Autotech Reading Limited | Wholesale & retail | 2009 |
| Autotech Slough Ltd | Wholesale & retail | 2000 |
| Autoworks Bodyshop Ltd | Wholesale & retail | 2011 |
| Avalon Maintenance Limited | Administrative & support | 2010 |
| Avancez Ltd | Professional & scientific | 2022 |
| Avanti Hairdressing Ltd | Other services | 2022 |
| Avb-Lab Limited | Professional & scientific | 2026 |
| Avelin Partners Ltd | Information & communication | 2025 |
| Avery Estate Management Limited | Real estate | 2026 |
| Avetta Limited | Professional & scientific | 2011 |
| Avexus Ltd | Professional & scientific | 2006 |
| Avhub Tech Limited | Wholesale & retail | 2021 |
| Aviateq Aviation Limited | Administrative & support | 2023 |
| Aviateq International Limited | Other services | 2003 |
| Aviateq Limited | Extraterritorial | 2006 |
| Aviationops Consulting Ltd | Professional & scientific | 2025 |
| Avidmode Ltd. | Information & communication | 2013 |
| Avire Limited | Manufacturing | 1971 |
| Avire Trading Limited | Manufacturing | 2016 |
| Avis Insurance Services Limited | Financial services | 1983 |
| AVK Energy Solutions Holdco Limited | Administrative & support | 2025 |
| AVK Group Services Limited | Financial services | 2026 |
| AVK Modular Services Limited | Manufacturing | 2025 |
| AVK Operating Group Limited | Administrative & support | 2025 |
| AVK Power Services Limited | Manufacturing | 2006 |
| AVK Power Solutions Limited | Manufacturing | 2023 |
| AVK Standby (UK) Limited | Manufacturing | 2024 |
| AVK Standby Holdco Limited | Administrative & support | 2025 |
| Avk/Seg Limited | Manufacturing | 1989 |
| Avocado and Spice Limited | Wholesale & retail | 2021 |
| Avonmoore Residents Association Company Limited | Households | 1993 |
| Avtico Limited | Manufacturing | 2013 |
| AW Business Solutions Ltd | Professional & scientific | 2020 |
| Awanova Limited | Wholesale & retail | 2026 |
| Awen Creatives Limited | Health & social care | 2022 |
| Awevo Films Ltd | Information & communication | 2019 |
| AWM Leisure and Retail Limited | Hospitality | 2018 |
| Ax-S International Limited | Professional & scientific | 2023 |
| AXL Properties Ltd | Real estate | 2025 |
| Axon Consulting Ltd | Administrative & support | 2004 |
| AXY Marketing Ltd | Information & communication | 2024 |
| Ayara Modest Wear Ltd | Wholesale & retail | 2025 |
| AYE Inc Ltd | Real estate | 2025 |
| Ayss Cakes Limited | Manufacturing | 2021 |
| AZ Digital Services Ltd | Information & communication | 2025 |
| Azraq True Ltd | Real estate | 2025 |
| Azumi.Io Limited | Information & communication | 2020 |
| Azure Knights Real Estate Ltd | Real estate | 2021 |
| B & D LE Fleming Services Limited | Professional & scientific | 2017 |
| B & L Emmett LLP | | 2019 |
| B & M Developments (Berkshire) Limited | Real estate | 2016 |
| B BOP Cosmetics Ltd | Wholesale & retail | 2018 |
| B K Transmissions Limited | Wholesale & retail | 2008 |
| B Linnett Electricians Ltd | Construction | 2019 |
| B Webster Services Ltd | Construction | 2022 |
| B-Stock Solutions Ltd | Wholesale & retail | 2015 |
| B.M. Kitchen Installations Ltd | Construction | 2011 |
| B.S. Bennett Limited | Real estate | 2003 |
| B7 Enterprises Limited | Financial services | 2002 |
| B7 Media Limited | Extraterritorial | 2008 |
| B7 Productions Limited | Information & communication | 2002 |
| Babasnug Limited | Professional & scientific | 2020 |
| Baboca Limited | Manufacturing | 2019 |
| Babos Bookkeeping Ltd | Professional & scientific | 2025 |
| Backabush Xplorers Ltd | Administrative & support | 2008 |
| Backplane Software Ltd | Information & communication | 2023 |
| Backward Trading Ltd | Wholesale & retail | 2024 |
| Baders Construction Limited | Construction | 2003 |
| Badnell Properties Limited | Real estate | 1961 |
| Bagster and Skwig Limited | Information & communication | 2020 |
| Baigstar Ltd | Wholesale & retail | 2021 |
| Bakedd Franchising Ltd | Administrative & support | 2025 |
| Bakedd Limited | Hospitality | 2017 |
| Baker Aventine Limited | Administrative & support | 2025 |
| Baker Productions Ltd | Manufacturing | 2021 |
| Bakt Limited | Real estate | 2025 |
| Bala Only Limited | Wholesale & retail | 2026 |
| Balaji Education Services LLP | | 2025 |