| Air 3 Group Limited | Construction | 2026 |
| Aircrew Hacks UK Limited | Professional & scientific | 2018 |
| AJ Project Services Ltd | Information & communication | 2023 |
| AJA Digital Limited | Administrative & support | 2013 |
| AJA Skills Assessment Ltd | Professional & scientific | 2026 |
| AJF Property Services Ltd | Administrative & support | 1997 |
| AJG Healthcare Limited | Health & social care | 2008 |
| Ajip Consulting Limited | Professional & scientific | 2018 |
| AJL Action Ltd | Information & communication | 2022 |
| AJM (2016) Limited | Construction | 2016 |
| AJR Renovations Limited | Construction | 1978 |
| AJS Mechanical and Electrical Limited | Construction | 2018 |
| AK Global Supplies Ltd | Wholesale & retail | 2024 |
| AK Luxury Design Limited | Professional & scientific | 2023 |
| Akay 2023 Ltd | Hospitality | 2023 |
| AKB Construction Limited | Construction | 2022 |
| Akra Investments Limited | Real estate | 2025 |
| Akshar Nivas Limited | Real estate | 2015 |
| Aksu Property Limited | Real estate | 2017 |
| Al-Kiramah Ltd | Real estate | 2024 |
| Alan Spivack Limited | Wholesale & retail | 1973 |
| Albans Lakes Ltd | Agriculture & fishing | 2018 |
| Alder Design and Construction Ltd | Construction | 2025 |
| Alders Moorings Management Limited | Real estate | 2026 |
| Alessia's Restaurant Ltd | Hospitality | 2023 |
| Alex Damms Ltd. | Information & communication | 2015 |
| Alexander Investment Energy Ltd | Financial services | 2021 |
| Alexanderq Ltd | Financial services | 2022 |
| Alexandria Imaging Ltd | Health & social care | 2010 |
| Align Pilates Studio London Limited | Arts & recreation | 2025 |
| Aligned Learning LAB Ltd | Professional & scientific | 2026 |
| ALL About Ice Europe Limited | Wholesale & retail | 2009 |
| ALL Pro Roofing & Decorating Limited | Construction | 2019 |
| ALL Seasons Heating & Cooling Limited | Construction | 2024 |
| ALL the FUN Things Ltd | Wholesale & retail | 2025 |
| Allday Temps Limited | Administrative & support | 2020 |
| Allens Catering Hire Services Limited | Hospitality | 1986 |
| Allens Holdings Limited | Other services | 1998 |
| Allgeo Ltd | Transport & logistics | 2018 |
| Alliance Consulting Real Estate Management and Laboratories Limited | Extraterritorial | 2012 |
| Alma Rising CIC | Health & social care | 2025 |
| Alma Verde Advisors Limited | Professional & scientific | 2017 |
| Almo Creates Limited | Manufacturing | 2024 |
| Alni Consultant UK Limited | Professional & scientific | 2020 |
| Alpha Joy Ltd | Construction | 2015 |
| Alpha Lambda Consulting Ltd | Professional & scientific | 2020 |
| Alpha Omega Education Ltd | Professional & scientific | 2024 |
| Alpha Toys Limited | Wholesale & retail | 2007 |
| Alpha Transfers Ltd | Transport & logistics | 2019 |
| Alppads Ltd | Other services | 2022 |
| Alta Vista Properties Limited | Real estate | 2021 |
| Altair Court RTM Company Limited | Households | 2024 |
| Altanova Holdings Limited | Financial services | 2025 |
| Altway Business Services Limited | Administrative & support | 2022 |
| Alyson House RCH Ltd | Health & social care | 2016 |
| AM Caravans Nationwide Ltd | Real estate | 2025 |
| AM Global Sourcing Limited | Wholesale & retail | 2025 |
| AM Interpreting Limited | Professional & scientific | 2012 |
| Amath Business Solutions Ltd | Other services | 2014 |
| Amazon Autos Limited | Wholesale & retail | 2018 |
| Ambassador Lift Company Limited | Professional & scientific | 2010 |
| Ambisaw Limited | Professional & scientific | 2013 |
| Ameliaa Limited | Information & communication | 2021 |
| Amersham TAE Kwon DO Limited | Arts & recreation | 2008 |
| AMH Planning Services (Rickmansworth) Ltd | Construction | 2016 |
| Amigo Business Solutions Ltd | Information & communication | 2026 |
| Amit Ltd | Health & social care | 2015 |
| Amitshah Ltd | Information & communication | 2023 |
| Amkmh Ltd | Health & social care | 2026 |
| Amma Building Ltd | Construction | 2025 |
| Ammser Limited | Real estate | 2020 |
| Amore Minis Ltd | Wholesale & retail | 2021 |
| Ampersand Technologies Ltd | Information & communication | 2025 |
| Amplio (Amersham) Limited | Construction | 2017 |
| Amplio Hampden Ltd | Real estate | 2023 |
| Amplio Investments Limited | Real estate | 2020 |
| Ampm IT Services Limited | Administrative & support | 2011 |
| Amra Properties Ltd | Real estate | 2018 |
| AMS (Hertfordshire) Limited | Professional & scientific | 2010 |
| AMS SPV One Ltd | Construction | 2021 |
| Amsay Ltd | Real estate | 2016 |
| Amsi Consulting Ltd | Real estate | 2017 |
| Amstran Assets Limited | Real estate | 2004 |
| Amstran Group Ltd | Financial services | 2021 |
| Amstran Properties Ltd | Real estate | 2014 |
| AN Medical Services Ltd | Health & social care | 2022 |
| AN PHU Minh Ltd | Other services | 2023 |
| ANA Technology Consultants Ltd | Information & communication | 2013 |
| Anaya Advisory Ltd | Professional & scientific | 2026 |
| Anbaric Limited | Information & communication | 2025 |
| Anceloti Security Limited | Administrative & support | 2025 |
| Andreas Franz Limited | Arts & recreation | 2026 |
| Andrew Construction Limited | Construction | 2007 |
| Andrew Large Consulting Limited | Professional & scientific | 2016 |
| Androsurg Ltd | Professional & scientific | 2016 |
| Andy Avis Electrical Limited | Construction | 2015 |
| Anelixis Mental Consulting Limited | Health & social care | 2024 |
| Anello Communications Ltd | Wholesale & retail | 2007 |
| Angel Audio Video Limited | Wholesale & retail | 2020 |
| Angel Digital Assets Limited | Financial services | 2020 |