| Action for Family Carers | Health & social care | 2008 |
| Active Mortgage Co. Limited | Other services | 2008 |
| Acufy Limited | Health & social care | 2024 |
| AD Fabrication Limited | Manufacturing | 1991 |
| AD Mech Ltd | Construction | 2026 |
| AD Property 1 Limited | Real estate | 2016 |
| AD Property 4 Limited | Real estate | 2017 |
| AD Property 5 Limited | Real estate | 2026 |
| Adam Clarke Haulage Ltd | Transport & logistics | 2026 |
| Adam Herbert Design Limited | Professional & scientific | 2010 |
| Addrestic Limited | Administrative & support | 2023 |
| Adhesion Release London Ltd | Health & social care | 2025 |
| ADM Engineering Services Limited | Manufacturing | 2005 |
| Adnatura Ltd | Real estate | 2024 |
| Adorn Estates Ltd | Real estate | 2019 |
| ADP Plumbing & Heating Ltd | Construction | 2019 |
| Adrian Ayley (UK) Limited | Wholesale & retail | 1998 |
| Adrian Bird Limited | Information & communication | 2009 |
| Advance Construction Advisors Ltd | Professional & scientific | 2023 |
| Advanced Cutting Technology Limited | Manufacturing | 1996 |
| Advocate Apparel Ltd | Wholesale & retail | 2023 |
| AEI Holdingco Limited | Financial services | 2026 |
| AEI Investco Limited | Construction | 2026 |
| AEO Pro Limited | Manufacturing | 2013 |
| Affordable Scaffolding Solutions Ltd | Construction | 2025 |
| Agricultural Facilities Limited | Real estate | 2006 |
| Agrifusion Limited | Agriculture & fishing | 1991 |
| AHA Bazaar Limited | Wholesale & retail | 2020 |
| Ainsworth Technical Services Ltd | Manufacturing | 2018 |
| Air Conditioning & Refrigeration Aircare Limited | Energy | 2003 |
| Air Domestique Limited | Manufacturing | 1981 |
| Airborne Business Group Ltd | Administrative & support | 2022 |
| AJC Pest Control Ltd | Professional & scientific | 2006 |
| Ajit Killy Limited | Health & social care | 2013 |
| Ajls Properties Limited | Real estate | 2018 |
| AKC Design Limited | Wholesale & retail | 2013 |
| Alaia Group Ltd | Construction | 2024 |
| Alark Consultancy Limited | Professional & scientific | 2023 |
| Albatross Marine Ltd | Manufacturing | 2024 |
| Albion Green Investments Ltd | Extraterritorial | 2009 |
| Alchemize Limited | Water & waste | 2001 |
| Alchemy & Stone Limited | Extraterritorial | 2020 |
| Alco Facilities Management Ltd | Construction | 2020 |
| Alderten Investments Limited | Construction | 2003 |
| Alderten Limited | Administrative & support | 1981 |
| Alea Services Ltd | Transport & logistics | 2016 |
| Alexandra Bence Limited | Professional & scientific | 2014 |
| Algam Ashdown Limited | Manufacturing | 1995 |
| Alieez Investment Limited | Real estate | 2023 |
| ALL About Aggregates Ltd | Administrative & support | 2017 |
| ALL About Dogs Limited | Professional & scientific | 2011 |
| ALL Saints Management (Maldon) Limited | Households | 2019 |
| ALL Things Pretty Limited | Wholesale & retail | 2018 |
| Allanfa Limited | Real estate | 2026 |
| Allclad Solutions Ltd | Construction | 2019 |
| Allen Speech & Language Ltd | Education | 2013 |
| Allengray Kitchens Limited | Manufacturing | 2002 |
| Allhandit Limited | Information & communication | 2012 |
| Allin House (Maldon) Management Company Limited | Households | 2017 |
| Allthread Plastics Limited | Administrative & support | 1982 |
| Allwood Holdings Limited | Professional & scientific | 2003 |
| Allwood Machinery Essex Limited | Manufacturing | 1997 |
| Allwood Machinery Limited | Extraterritorial | 1984 |
| Almar Investments Limited | Real estate | 2000 |
| Alpha Property Maintenance Ltd | Manufacturing | 2020 |
| Alpine UK Scaffolding Ltd | Construction | 2022 |
| Alpine View Holdings Limited | Financial services | 2025 |
| Alpstone Properties Limited | Real estate | 2026 |
| Altacus Limited | Administrative & support | 2018 |
| Alter-Nation Ltd | Other services | 2023 |
| Alterrain Ltd | Construction | 2024 |
| Althorne Marine Services (Mechanical) Limited | Manufacturing | 2010 |
| AM Electrical & Property Solutions Ltd | Construction | 2023 |
| AM Tech and Tyres Ltd | Wholesale & retail | 2025 |
| Amaric Limited | Professional & scientific | 2007 |
| Amaya MH Ltd | Other services | 2023 |
| Amber House (Maldon) Limited | Households | 2022 |
| Ambient Flooring Limited | Construction | 2016 |
| Ambrose and Sons Ltd | Professional & scientific | 2024 |
| AMD Sport Services Ltd | Manufacturing | 2019 |
| AME (DAC) Limited | Construction | 2001 |
| AME Railways Limited | Construction | 2021 |
| AMP Global Holdings Ltd | Financial services | 2024 |
| Amplified Commercial Services Ltd | Professional & scientific | 2025 |
| AMR Motorsport Ltd | Wholesale & retail | 2022 |
| Amsa Consulting Ltd | Other services | 2011 |
| Amtest UK Ltd. | Professional & scientific | 2020 |
| Amto Properties Limited | Households | 2017 |
| Amy's Nails & Spa Ltd | Other services | 2016 |
| Anchor Creative Ltd | Professional & scientific | 2019 |
| Ancos Solutions Ltd | Professional & scientific | 2012 |
| Andar Group Ltd | Information & communication | 2023 |
| Andar Logistics Limited | Wholesale & retail | 2024 |
| Andrew & Albert Limited | Manufacturing | 2013 |
| Andrew Day Arboricultural Consultancy Limited | Agriculture & fishing | 2009 |
| Andrew Miller MAC Tools Limited | Wholesale & retail | 2024 |
| Andrew Watson and SON Limited | Construction | 2011 |
| Andy Little Holdings Limited | Financial services | 2026 |
| Andy Little Properties Ltd | Real estate | 2025 |
| Anewko Ltd | Manufacturing | 2024 |