| ARB Enterprises Limited | Wholesale & retail | 2024 |
| Archers Properties Limited | Construction | 2012 |
| Archie Davies CAD Ltd | Professional & scientific | 2025 |
| Archlinks Ltd | Construction | 2019 |
| Arcomedical Infusion Limited | Manufacturing | 1992 |
| Area P Limited | Financial services | 2023 |
| Arek Ltd | Construction | 2015 |
| Arete Health Coaching Ltd | Health & social care | 2025 |
| ARI Crown Trading Co., Ltd | Wholesale & retail | 2025 |
| Aria's Hair Lounge Ltd | Other services | 2023 |
| Ariadne Auclair Limited | Wholesale & retail | 2025 |
| Aries Town and Country Homes Ltd | Real estate | 2019 |
| Arizuma Research Ltd | Wholesale & retail | 2022 |
| Arkema Bostik UK Pension Trustee Limited | Professional & scientific | 2014 |
| Arkema Holding Limited | Professional & scientific | 1966 |
| Arkema UK Limited | Manufacturing | 2011 |
| Armadillo PUB Company Ltd | Hospitality | 2025 |
| Armoured Limited | Construction | 2019 |
| Aroma by Tranquility Limited | Wholesale & retail | 2013 |
| Arredamento Design Ltd | Extraterritorial | 2022 |
| Arrowmaker Pubs Ltd | Hospitality | 2019 |
| Arthur Aniagoh Ltd | Wholesale & retail | 2025 |
| Arthur Ellis Consultants Ltd | Professional & scientific | 2018 |
| Artifex Innovation Group Limited | Wholesale & retail | 2025 |
| Artisans of Innovation Ltd | Professional & scientific | 2020 |
| Arvex Trading Co., Limited | Wholesale & retail | 2025 |
| Arya Professionals Limited | Health & social care | 2012 |
| Aryara Group Limited | Manufacturing | 2025 |
| AS One Import and Export Co., Ltd | Manufacturing | 2025 |
| AS Universal Imports Ltd | Transport & logistics | 2025 |
| ASA Productions (UK) Limited | Information & communication | 2004 |
| Asap Trees & Landscaping Ltd | Administrative & support | 2025 |
| Ascend Ecommerce Intelligence Limited | Administrative & support | 2021 |
| Ascendz Digital Limited | Professional & scientific | 2026 |
| Ascent Primary Healthcare Limited | Health & social care | 2024 |
| Ascot Business Solutions Limited | Wholesale & retail | 2004 |
| Ascot Property and Investment Services Ltd | Administrative & support | 2008 |
| ASF Hospitality Limited | Hospitality | 2025 |
| ASG Management Ltd | Transport & logistics | 2025 |
| Asgard Fire Protection Ltd | Public administration | 2022 |
| Asgard Plant Ltd | Construction | 2025 |
| ASH House Care Ltd | Health & social care | 2020 |
| ASH House Holdings Ltd | Real estate | 2022 |
| ASH Wall Music Limited | Arts & recreation | 2024 |
| Ashdown Bulk Haulage Limited | Transport & logistics | 2021 |
| Ashemac Limited | Information & communication | 2007 |
| Ashington Electrical Ltd | Construction | 2021 |
| Ashley Bates Property Limited | Construction | 2025 |
| Ashley Insurance Services Limited | Financial services | 1987 |
| Ashstone Myers Limited | Real estate | 2021 |
| Ashton Sinha Limited | Real estate | 2025 |
| Ashton Stone Myers Limited | Financial services | 2024 |
| Ashwood Equestrian Ltd | Arts & recreation | 2011 |
| Asia Cargo Limited | Wholesale & retail | 2022 |
| Asia Pacific Import and Export Limited | Wholesale & retail | 2025 |
| Asia Pacific Ocean Group Co., Ltd | Extraterritorial | 2016 |
| Asia Seafood Group Ltd | Extraterritorial | 2016 |
| Asian Academy of Arts Ltd | Administrative & support | 2024 |
| Asilia Limited | Wholesale & retail | 2021 |
| Asiya International Co., Ltd | Wholesale & retail | 2024 |
| ASJ Traders Limited | Wholesale & retail | 2025 |
| ASK2 Social Media Ltd | Information & communication | 2020 |
| ASM Motor Repairs Limited | Wholesale & retail | 2008 |
| Aspinall Creative Ltd | Construction | 2016 |
| Aspira Mortgage and Protection Advice Ltd | Financial services | 2026 |
| Aspirational Properties Limited | Real estate | 2023 |
| Aspire (Stafford) Limited | Education | 2016 |
| Aspire for Excellence Ltd | Extraterritorial | 2017 |
| Aspley Enterprises Limited | Agriculture & fishing | 2004 |
| Assens Technology Co., Ltd | Manufacturing | 2023 |
| Assisted Living Bathrooms Limited | Construction | 2024 |
| ASSOCI8 Solutions Limited | Administrative & support | 2008 |
| Assure Fire Safety Training Ltd | Public administration | 2019 |
| Assured Networks Ltd | Construction | 2021 |
| Astley Holdings Limited | Construction | 2023 |
| Aston Alloys (Properties) Limited | Real estate | 2010 |
| Aston Alloys Holdings Limited | Financial services | 2025 |
| Aston Alloys Limited | Wholesale & retail | 2007 |
| Aston Farm Plant Ltd | Construction | 2023 |
| Aston Hanover Limited | Manufacturing | 2021 |
| Aston Homes (Staffs) Limited | Construction | 2001 |
| Aston Marina Limited | Hospitality | 2008 |
| Astraldale Web Services Limited | Information & communication | 2025 |
| Astro Products Ltd | Extraterritorial | 2015 |
| Asza Ltd | Wholesale & retail | 2019 |
| AT Commercial Interiors Limited | Construction | 2012 |
| AT Prestige Ltd | Transport & logistics | 2025 |
| AT the Box Ltd | Other services | 2017 |
| AT the Dog House Haughton Limited | Wholesale & retail | 2025 |
| ATC Property Holdings Limited | Real estate | 2018 |
| Athanatou Lettings Ltd | Real estate | 2024 |
| Atlantic Financial Group Limited | Extraterritorial | 2017 |
| Atlas Coating Limited | Manufacturing | 2000 |
| Atlas Kebab House Limited | Hospitality | 2017 |
| Atlas Property Consultants Limited | Professional & scientific | 2012 |
| Atozpro Trading Co., Limited | Manufacturing | 2025 |
| Atpro Group Limited | Wholesale & retail | 2025 |
| ATS Building Developments Limited | Construction | 2009 |
| ATTACH2UK Ltd | Wholesale & retail | 2023 |
| Auchi Auto Parts Co., Ltd | Wholesale & retail | 2022 |