| Alistair Upcraft Ltd | Information & communication | 2005 |
| ALL Arcs Ltd | Professional & scientific | 2024 |
| ALL Things Water Ltd | Construction | 2021 |
| Alliedtrace Limited | Real estate | 1998 |
| Alloro Delivery Restaurant Ltd | Hospitality | 2019 |
| Allplas.Co.Uk Limited | Administrative & support | 2003 |
| ALN Associates Limited | Administrative & support | 2025 |
| Alpaca Lodge Limited | Agriculture & fishing | 2022 |
| Alpha Visual Limited | Information & communication | 2012 |
| Alphr Technology Limited | Manufacturing | 1994 |
| Altay Services Ltd | Health & social care | 2024 |
| Alternative Glass Works Ltd | Construction | 2012 |
| Alternative Outlet Limited | Wholesale & retail | 2024 |
| Altro Floors Limited | Professional & scientific | 1968 |
| Altro Whiterock Limited | Professional & scientific | 1963 |
| Altrofix Limited | Extraterritorial | 1980 |
| Altrosport Surfaces Limited | Extraterritorial | 1927 |
| Alyssum Properties Limited | Real estate | 2026 |
| AM Global Partners Limited | Financial services | 2025 |
| AM Martec Ltd | Professional & scientific | 2025 |
| Aman Holdings Limited | Real estate | 2024 |
| Amaz-Ballz Ltd | Hospitality | 2024 |
| Amber Electrical Services (Beds) Ltd | Construction | 2021 |
| Amberskye Designs Limited | Professional & scientific | 2024 |
| Amco Facilities Management Limited | Information & communication | 1996 |
| Amescar Ltd | Real estate | 2024 |
| Ammavaru Jewellery Ltd | Wholesale & retail | 2016 |
| Ampyr DG UK ASSETCO1 Limited | Professional & scientific | 2023 |
| Ampyr Distributed Energy 1 Ltd | Professional & scientific | 2024 |
| Ampyr Distributed Energy 2 Ltd | Professional & scientific | 2024 |
| Ampyr Distributed Energy Finco Limited | Financial services | 2024 |
| Ampyr Idea Assetco UK Ltd | Financial services | 2023 |
| Ampyr Idea UK Ltd | Professional & scientific | 2023 |
| Amugold Global Network Ltd | Wholesale & retail | 2024 |
| Amys Electrical and Building Limited | Construction | 2017 |
| Anaikam Ltd | Real estate | 2018 |
| Anchor & Standard Ltd | Hospitality | 2026 |
| Anchorspace Ltd | Real estate | 2024 |
| Andrew COX Cmli Limited | Professional & scientific | 2025 |
| Andrew Foreman Garden Plants Ltd | Wholesale & retail | 2026 |
| Andrew Stevenson Developments Ltd | Construction | 2014 |
| Anglo-Dutch Property (UK) Holding Limited | Real estate | 1985 |
| Anneo Consulting Ltd | Information & communication | 2018 |
| ANV Phase 4 Holdings Limited | Construction | 2024 |
| ANV Phase 4 LLP | | 2024 |
| AO Property Partners Ltd | Real estate | 2025 |
| APA Ecommerce Ltd | Wholesale & retail | 2025 |
| Apertum Solutions Ltd | Professional & scientific | 2016 |
| Apex Centre Ltd | Real estate | 2021 |
| Apogee International Limited | Wholesale & retail | 1994 |
| Apogii Ltd | Health & social care | 2017 |
| Apoise Ltd | Other services | 2017 |
| Apollo IT GAP Ltd | Information & communication | 2025 |
| Applied Pipeline Technologies Limited | Wholesale & retail | 2021 |
| Aptech Systems Limited | Information & communication | 2009 |
| Aptus Building and Design Limited | Construction | 2003 |
| Aquaplus Solutions Ltd | Wholesale & retail | 2002 |
| Ar-Speed Ltd | Transport & logistics | 2017 |
| Arbon Property Ltd | Real estate | 2019 |
| ARC Digital Marketing Limited | Administrative & support | 2023 |
| Archaeologistics Limited | Professional & scientific | 1997 |
| Architech Building Design Consultants Limited | Professional & scientific | 2002 |
| Ardross Autos Ltd | Manufacturing | 2013 |
| Argon Ltd | Manufacturing | 2024 |
| Argonaut Partners Ltd | Professional & scientific | 2026 |
| Arkk Holdings Limited | Financial services | 2025 |
| Arnolds Close Management Limited | Households | 2021 |
| Artemis Group Developments Ltd | Real estate | 2025 |
| Artybubbas Ltd | Arts & recreation | 2023 |
| Arune Ltd | Professional & scientific | 2008 |
| AS Nagra Ltd | Construction | 2014 |
| AS1SPORTS Limited | Professional & scientific | 2022 |
| Ashiyana Estates Limited | Real estate | 2024 |
| ASL Tech Ltd | Information & communication | 2025 |
| ASP Carpentry Solutions Limited | Construction | 2006 |
| Aspenden Hall Farm Limited | Agriculture & fishing | 1978 |
| Aspenden Trading Limited | Extraterritorial | 1959 |
| Aspire Children Limited | Health & social care | 2025 |
| ASR1 Limited | Health & social care | 2021 |
| ASR1 Properties Limited | Real estate | 2023 |
| Assetfirst Portfolios LLP | | 2010 |
| Assigns Associates Limited | Real estate | 2011 |
| AT & RT Property Ltd | Real estate | 2026 |
| Atec M&E Ltd | Construction | 2019 |
| Atlantis Fish Ltd | Hospitality | 2024 |
| Atles Shipping Ltd | Transport & logistics | 2023 |
| Atrone Tech Ltd | Manufacturing | 2025 |
| Aujla Capital Limited | Real estate | 2026 |
| Auntie Kitty Enterprises Ltd | Hospitality | 2026 |
| Aurelia Cosmetics Ltd | Other services | 2025 |
| Aurelius Hcig Limited | Administrative & support | 2017 |
| Austin House Hitchin Limited | Real estate | 2025 |
| Auto Enthusiasts LLP | | 2011 |
| Autoglym Limited | Professional & scientific | 1980 |
| Autoglym Products Limited | Professional & scientific | 1966 |
| AVC One Limited | Information & communication | 2013 |
| AVC Technical Services Limited | Other services | 2011 |
| AVC Weeeco Limited | Water & waste | 2010 |
| Avenue Billiard Club Limited | Arts & recreation | 2008 |
| Avenue Training Limited | Information & communication | 2007 |