| AGI Search Limited | Administrative & support | 2026 |
| Agility PR Solutions Limited | Professional & scientific | 2016 |
| Agricola Limited | Other services | 2019 |
| Agronaturalis Limited | Manufacturing | 2008 |
| Airius Europe Limited | Wholesale & retail | 2006 |
| Aivly Country Store Ltd | Wholesale & retail | 2002 |
| AJS Build & Design Ltd | Construction | 2023 |
| AK Genius Solutions Ltd | Professional & scientific | 2017 |
| AK Property Consultants Ltd | Professional & scientific | 2012 |
| Akercomb Bush Consulting Ltd | Administrative & support | 2019 |
| Alaska Wind Farm Limited Liability Partnership | | 2021 |
| Albany Associates International Limited | Professional & scientific | 2004 |
| Aldreth Developments Limited | Construction | 2020 |
| Aldreth Holdings Limited | Real estate | 2020 |
| Alecta Technical Solutions Ltd | Manufacturing | 2017 |
| Alfords Management Limited | Real estate | 2015 |
| Alice Creatives Ltd | Professional & scientific | 2023 |
| Align Motion Ltd | Administrative & support | 2025 |
| Aligned Design Studio Ltd | Professional & scientific | 2023 |
| ALL Aspect Media Limited | Professional & scientific | 2018 |
| ALL Aspects Electrical Services Ltd | Construction | 2011 |
| ALL Aspects Plumbing & Heating Ltd | Construction | 2008 |
| ALL Axis Studio Limited | Professional & scientific | 2021 |
| ALL Equal Limited | Professional & scientific | 2011 |
| ALL Occasions Laser Engraving Limited | Wholesale & retail | 2021 |
| ALL Star Entertainment (London) Ltd | Administrative & support | 2016 |
| Allclean Environmental Solutions Ltd | Wholesale & retail | 2024 |
| Alliance FX Limited | Financial services | 2019 |
| Alliance Metal Ltd | Construction | 2025 |
| ALT Solutions UK Ltd | Transport & logistics | 2020 |
| Altrullo Ltd | Hospitality | 2018 |
| Alzanti Ltd | Extraterritorial | 2012 |
| Ambassador Pools Group Limited | Administrative & support | 2010 |
| Amberley Court Freehold Limited | Households | 2003 |
| Amberwood RTM Limited | Households | 2010 |
| Ambridge & Partners LLP | | 2017 |
| AMI Group Holdings Ltd | Financial services | 2019 |
| Amonax Limited | Wholesale & retail | 2019 |
| Ampm Contractors Limited | Construction | 2017 |
| Analyse My Game Ltd | Education | 2025 |
| Andrea of Wembley (Watford) Limited | Other services | 2007 |
| Andrew Parker Services Ltd | Administrative & support | 2007 |
| Andrews Property Maintenance Ringwood Limited | Construction | 2017 |
| Andser Consulting Ltd | Professional & scientific | 2025 |
| Andy Barrett Ltd | Professional & scientific | 2011 |
| Angel Blossom Care Ltd | Health & social care | 2015 |
| Anglo Marquees & Events Limited | Arts & recreation | 2009 |
| Animal Avenue Pet Supplies Ltd | Wholesale & retail | 2024 |
| Animal Concern UK Limited | Real estate | 1997 |
| Anna Bridal Clubhouse Limited | Wholesale & retail | 2024 |
| Anna Bridal Couture Limited | Wholesale & retail | 2017 |
| Anna WAZ Styling Limited | Arts & recreation | 2020 |
| Annrose Limited | Professional & scientific | 2004 |
| Antepli Ringwood Ltd | Hospitality | 2023 |
| Anzeck Plastics Ltd | Manufacturing | 2019 |
| Aosoutdoorkitchens Ltd | Construction | 2019 |
| AP Heating Solutions Ltd | Construction | 2019 |
| Apeiron Catering Limited | Manufacturing | 2014 |
| Apollo Renewable Installations Ltd | Construction | 2023 |
| Appleslade Limited | Professional & scientific | 2015 |
| Applied Kinematics Limited | Professional & scientific | 1999 |
| Applify Marketing Limited | Professional & scientific | 2017 |
| Aquadeck International Ltd | Administrative & support | 2023 |
| Aquatech Surfacing Ltd | Other services | 2025 |
| Arch Collective Ltd | Real estate | 2012 |
| Aren Mahir Limited | Hospitality | 2020 |
| Argonaut Limited | Information & communication | 2006 |
| ARL 019 Limited | Energy | 2018 |
| Arlyhe Limited | Other services | 2025 |
| Arms Hospitality Ltd | Hospitality | 2020 |
| Artema Holdings Ltd | Professional & scientific | 2016 |
| Artema Limited | Professional & scientific | 2005 |
| Arthur Derek Property Holdings Ltd | Real estate | 2024 |
| Artie+Co Limited | Professional & scientific | 2025 |
| Artmag Water Tracing Ltd | Construction | 2026 |
| Arun Office Services Limited | Administrative & support | 2003 |
| AS PPC Services Ltd | Professional & scientific | 2022 |
| Asalive Limited | Arts & recreation | 2018 |
| ASC Consulting Limited | Information & communication | 2004 |
| Ashley Classics Limited | Wholesale & retail | 2019 |
| Ashley Heath Commercial Services Ltd | Extraterritorial | 2011 |
| Ashley Tree Surgeons Ltd | Agriculture & fishing | 2024 |
| Asjs Services Ltd | Other services | 2021 |
| Askmetiger Limited | Information & communication | 2022 |
| Aspect Lighting Limited | Construction | 2013 |
| Aspire Architects (Dorset) Limited | Professional & scientific | 2016 |
| Aspire Jobs Limited | Administrative & support | 2014 |
| Astron Digital Limited | Information & communication | 2024 |
| Asts Services Limited | Wholesale & retail | 2024 |
| AT Advisors Ltd | Professional & scientific | 2012 |
| AT Home in Lindley Ltd | Hospitality | 2020 |
| Atelier Resin Coatings Ltd | Construction | 2025 |
| Atheneys Law Limited | Financial services | 2018 |
| Atlantic Diesel Services Limited | Manufacturing | 2007 |
| Atlantis Electronics Limited | | 1986 |
| Atmospheres Air Conditioning Services Ltd | Construction | 2000 |
| Atmospheres Building Services Limited | Construction | 2015 |
| Atmospheres UK Ltd | Professional & scientific | 2005 |
| Auraria Limited | Health & social care | 2024 |
| Austen Meadows (Medstead) Management Company Limited | Households | 2016 |