| Assa Global Services Limited | Financial services | 2011 |
| Asset Management Partnership Ltd | Real estate | 2025 |
| Assetrock (UK) Limited | Real estate | 2015 |
| Assetrock Barking Ltd | Real estate | 2018 |
| Assetrock Billericay Ltd | Real estate | 2016 |
| Assetrock Consulting Limited | Real estate | 2016 |
| Assetrock Elite Limited | Real estate | 2016 |
| Assetrock Epping Ltd | Real estate | 2016 |
| Assetrock Essex Ltd | Real estate | 2018 |
| Assetrock Finance Ltd | Financial services | 2016 |
| Assetrock Holdings Ltd | Financial services | 2016 |
| Assetrock Investments Ltd | Real estate | 2017 |
| Assetrock Limited | Real estate | 2011 |
| Assetrock London Ltd | Real estate | 2016 |
| Assetrock Loughton 1 Ltd | Real estate | 2024 |
| Assetrock Loughton Ltd | Real estate | 2015 |
| Assetrock Maidstone Ltd | Real estate | 2018 |
| Assetrock Reading Limited | Real estate | 2021 |
| Assetrock Slough Ltd | Real estate | 2017 |
| Assetrock Sovereign House Ltd | Real estate | 2024 |
| Assetrock Swanley Ltd | Real estate | 2018 |
| Assetrock Thurrock Ltd | Real estate | 2019 |
| Assetrock Trump Ltd | Real estate | 2016 |
| Assetrock Upney Ltd | Real estate | 2015 |
| Assetrock Walthamstow Ltd | Real estate | 2017 |
| Associate Software Limited | Information & communication | 2007 |
| Associated Data Developments Limited | Information & communication | 1998 |
| Association for Accountancy & Business Affairs Ltd | Other services | 1997 |
| Association of Natural Medicines Limited | Health & social care | 1983 |
| Assured Security Solutions Ltd | Administrative & support | 2006 |
| Astat Ltd | Administrative & support | 2000 |
| Aston Insurance Brokers Limited | Construction | 1996 |
| Astonlaw Limited | Wholesale & retail | 1990 |
| Astra Good Limited | Hospitality | 2022 |
| Astral Style Group Ltd | Wholesale & retail | 2026 |
| Asuo Legal & Dispute Mediation Services Ltd | Professional & scientific | 2017 |
| Atelya Ltd | Hospitality | 2019 |
| Athenae Ltd | Other services | 2006 |
| Atijo Store Limited | Wholesale & retail | 2020 |
| Atilola Adeleke Healthcare Services Limited | Health & social care | 2025 |
| Atlantic Builders (UK) Limited | Construction | 2005 |
| Atlantis Property Management Ltd | Real estate | 2022 |
| Atlas Developments Ltd | Real estate | 2001 |
| Atomic Automation Ltd | Construction | 2014 |
| Aton Investments Limited | Real estate | 1971 |
| Attcost'E Limited | Construction | 1997 |
| Attractive Smiles Limited | Health & social care | 2021 |
| Attwood Business Consultancy Limited | Wholesale & retail | 1998 |
| AU Music Ltd | Information & communication | 2018 |
| Auckland Holdings Limited | Professional & scientific | 1990 |
| Auckland International Limited | Wholesale & retail | 1990 |
| Auckland.Com Limited | Professional & scientific | 2000 |
| Audio Craft Limited | Professional & scientific | 2000 |
| Audiogenic Software Limited | Information & communication | 1984 |
| Audley END Farming Limited | Agriculture & fishing | 2018 |
| AUG Capital Ltd | Financial services | 2024 |
| AUM Good Wealth Limited | Professional & scientific | 2002 |
| AUN Associates Ltd | Wholesale & retail | 2025 |
| Aura 360 Ltd | Information & communication | 2025 |
| Aura Painting Contractors Ltd | Construction | 2025 |
| Auratec Limited | Manufacturing | 2004 |
| Aurea Beauty UK Retail Ltd | Wholesale & retail | 2026 |
| Aurelia Investment Group Limited | Financial services | 2026 |
| Aurion Investments Limited | Real estate | 2002 |
| Aurora Court Management Limited | Real estate | 1995 |
| Aurum Pharmaceuticals Limited | Manufacturing | 1991 |
| Aussies Club Ltd | Wholesale & retail | 2026 |
| Austin Samuels Limited | Real estate | 2020 |
| Austin Universal Commerce Ltd | Wholesale & retail | 2023 |
| Austyn Smith Associates Limited | Professional & scientific | 2000 |
| Authorized Dealer Ltd | Wholesale & retail | 2025 |
| Auto Swift Sales Ltd | Wholesale & retail | 2026 |
| Autobreak (Colchester) Limited | Administrative & support | 2005 |
| Autolak Ltd | Wholesale & retail | 2005 |
| Automotive Recruitment Consultants Limited | Administrative & support | 2002 |
| Autonomus Car Parts Ltd | Wholesale & retail | 2026 |
| Autotest Limited | Wholesale & retail | 2001 |
| AV1 Electrics Limited | Construction | 2007 |
| AVC Capital Ltd | Financial services | 2022 |
| Avertt Ltd | Health & social care | 2024 |
| Avetax Ltd | Wholesale & retail | 2025 |
| Avian Rizky International Ltd | Information & communication | 2025 |
| Aviated Media Ltd | Information & communication | 2022 |
| Avista Technologies Ltd | Construction | 2022 |
| AVS Consultation Ltd | Real estate | 2025 |
| Awaan Care Ltd | Health & social care | 2024 |
| Awais Ayaz 76 Ltd | Wholesale & retail | 2026 |
| Awakening Time Ltd | Education | 2013 |
| Award Music Ltd. | Education | 2001 |
| Awards 4 ALL Limited | Wholesale & retail | 1993 |
| AWH Pools Limited | Construction | 2024 |
| Awning Company London Limited | Manufacturing | 2025 |
| Awobajo Brother's Limited | Wholesale & retail | 1999 |
| Awsem Ltd | Wholesale & retail | 2025 |
| Axcertro Limited | Information & communication | 2025 |
| Axel Bookkeeping Limited | Professional & scientific | 2004 |
| Axel Electrical Limited | Construction | 2006 |
| Axiomgrid Limited | Wholesale & retail | 2025 |
| AXO Trading Ltd | Information & communication | 2024 |
| Axovia Ltd | Wholesale & retail | 2026 |