| Alexander Risdon Property Consultancy Limited | Real estate | 2025 |
| Alfredson York Associates Limited | Professional & scientific | 2020 |
| Align Pilates Limited | Health & social care | 2008 |
| Alinio Ltd | Health & social care | 2011 |
| Alison Finch Ltd | Professional & scientific | 2026 |
| Alison Green Editorial Ltd | Information & communication | 2015 |
| Alison M Simmen Limited | Professional & scientific | 2002 |
| ALL Film Services Limited | Information & communication | 2012 |
| Allaway Management Limited | Real estate | 2013 |
| Allerium Limited | Other services | 2025 |
| Allie Campbell Limited | Public administration | 2026 |
| Allwhite Property Maintenance Ltd | Construction | 2012 |
| Almond Square Limited | Construction | 2025 |
| Alpha JET Charter Limited | Transport & logistics | 2009 |
| Alpha Secured Investments Limited | Financial services | 2020 |
| ALT Engage Limited | Information & communication | 2021 |
| ALT Recruitment Limited | Administrative & support | 2025 |
| Altitude FX Limited | Administrative & support | 2024 |
| Amanda Farmer Consultancy Limited | Professional & scientific | 2009 |
| Amba Beauty Limited | Wholesale & retail | 2024 |
| Ambleside Collection Ltd | Wholesale & retail | 2024 |
| Amicum Partners Limited | Financial services | 2024 |
| Amplify Media Works Ltd | Professional & scientific | 2025 |
| AMY Wiggin Pictures and Illustration Ltd | Administrative & support | 2019 |
| Ancastle Green Residents (Freehold) Limited | Real estate | 2025 |
| Andreas W. Klatt Limited | Administrative & support | 1987 |
| Andrew Stanley Limited | Education | 2015 |
| Anglo Asia Forestry Company Limited | Agriculture & fishing | 2008 |
| Anglo Consulting Group Ltd | Professional & scientific | 2016 |
| Anjuna Solutions UK Limited | Other services | 2023 |
| Anne Haimes Interiors Limited | Professional & scientific | 2001 |
| Annie's Portb Ltd | Real estate | 2025 |
| Anonymous Coffee Limited | Manufacturing | 2021 |
| Aphot Ltd | Professional & scientific | 2015 |
| Apointe Limited | Administrative & support | 2025 |
| Apperley Wealth Management Limited | Professional & scientific | 2023 |
| Appy Design Ltd | Information & communication | 2020 |
| Aqua Irrigation Systems Limited | Administrative & support | 2022 |
| Aquatronic Group Management Limited | Manufacturing | 1997 |
| Aquila Energy Group Ltd | Financial services | 2023 |
| AR GTM Advisory Ltd | Administrative & support | 2022 |
| Arcanum Consulting Ltd | Professional & scientific | 2013 |
| Archers Rise (Witney) Management Company Limited | Households | 2005 |
| Archway Court (Marlow) Management Company Ltd | Households | 2024 |
| Aromathea Ltd | Wholesale & retail | 2025 |
| Artandevents Ltd | Professional & scientific | 2025 |
| Artelevate Ltd | Construction | 2024 |
| Aryaman Group Holdings Ltd | Financial services | 2025 |
| Aryaman UK Holdings Ltd | Financial services | 2025 |
| ASG Logistics Holdings Limited | Transport & logistics | 2023 |
| ASG Logistics Limited | Transport & logistics | 2004 |
| Ashdown Restorations Limited | Real estate | 2003 |
| Ashifah Dhalla Design & Architecture Ltd | Professional & scientific | 2018 |
| Ashpropuk Ltd | Extraterritorial | 2024 |
| Ashua Consultancy Ltd | Professional & scientific | 2019 |
| Ashworth House RTM Company Limited | Households | 2021 |
| Asiana Spice (DB) Ltd | Hospitality | 2018 |
| Asiana Spice (Henley) Ltd | Hospitality | 2019 |
| Asiana Spice (Thames) Ltd | Hospitality | 2023 |
| ASPIRE2B Futures Ltd | Education | 2022 |
| Assendon Management Systems Limited | Information & communication | 2013 |
| Asset Clearing Network Ltd | Information & communication | 2026 |
| Asset Management Consultancy Services Limited | Professional & scientific | 2026 |
| Assistmed (UK) Limited | Professional & scientific | 2019 |
| Associated Asphalt Limited | Extraterritorial | 1997 |
| Associated Environmental Limited | Professional & scientific | 1997 |
| Associated Holdings Limited | Professional & scientific | 1996 |
| Associated Properties Henley Limited | Extraterritorial | 1997 |
| AT the Limits Limited | Hospitality | 2010 |
| Atelier Konte Limited | Professional & scientific | 2020 |
| Athletes Inbalance Ltd | Health & social care | 2020 |
| Atlantic House London Limited | Households | 2002 |
| Atmosphere Labs Ltd | Information & communication | 2026 |
| Atrio Architecture Ltd | Professional & scientific | 2024 |
| Atticus and Hope Limited | Wholesale & retail | 2021 |
| Aubisque Ltd | Administrative & support | 2018 |
| Audim Limited | Information & communication | 2008 |
| Aura Creative Ltd | Professional & scientific | 2009 |
| Austin MAY Medical Ltd | Administrative & support | 2013 |
| Autostorico Limited | Wholesale & retail | 2017 |
| Autostorico Partners LLP | | 2021 |
| Autotint Limited | Extraterritorial | 1994 |
| Avella Construction Limited | Manufacturing | 2015 |
| Avenir X Ltd | Professional & scientific | 2023 |
| Aviatrice Limited | Professional & scientific | 2015 |
| Avoro Ltd | Information & communication | 2025 |
| Avsec Resilience Limited | Administrative & support | 2013 |
| Awatea Holdings Ltd | Real estate | 2025 |
| Axel Olivier Ltd | Wholesale & retail | 2026 |
| Ayspark Ltd | Information & communication | 2009 |
| B & C Builders Limited | Construction | 1997 |
| B Plus C Limited | Professional & scientific | 2012 |
| B&B General Service Ltd | Construction | 2021 |
| B&J Locket Limited | Arts & recreation | 2023 |
| B.D. Rentals Ltd | Real estate | 2022 |
| Babyboomboom Limited | Administrative & support | 2005 |
| Backlot Technologies Limited | Information & communication | 2025 |
| Badgemore Holdings Limited | Professional & scientific | 2005 |
| Balanced Bodyworks Limited | Health & social care | 2003 |
| Ballards Estate Agents Limited | Real estate | 1998 |