| Assandune Limited | Professional & scientific | 2011 |
| Assco Care Ltd | Health & social care | 2021 |
| Asset Care London Ltd | Construction | 2026 |
| Asset Exchange Holdings Limited | Financial services | 2016 |
| Asset Finance.Co.Uk. Limited | Financial services | 2019 |
| Assets for Management Ltd | Real estate | 2021 |
| Assetsforinvestments Ltd | Real estate | 2019 |
| Associated Motor Cycles Limited | Professional & scientific | 2009 |
| Association of Consultant Architects Limited(The) | Other services | 1978 |
| Assurance Business Consultancy Limited | Professional & scientific | 2009 |
| Assured Bricklayers & Carpenters Limited | Construction | 1996 |
| Assured Contractors Limited | Manufacturing | 2012 |
| AST Logistics Solutions Ltd | Transport & logistics | 2026 |
| AST Property Group Limited | Construction | 2026 |
| AST Villas Ltd | Real estate | 2023 |
| Aston Bridges Group Ltd | Hospitality | 2024 |
| Aston Mayfield Limited | Professional & scientific | 2025 |
| Astonmorg Limited | Administrative & support | 2014 |
| Astra Rise Limited | Wholesale & retail | 2025 |
| Astra Tech International Ltd | Information & communication | 2023 |
| Astur Design Limited | Professional & scientific | 2014 |
| AT & T Healthcare Limited | Health & social care | 2014 |
| Atal Engineering (UK) Limited | Professional & scientific | 2026 |
| ATF Scaffolding Limited | Construction | 2017 |
| ATG 13 Limited | Wholesale & retail | 2017 |
| ATH Construction Limited | Construction | 2019 |
| Athena Care Homes (Arbury) Limited | Health & social care | 2023 |
| Athena Care Homes (Bretton) Limited | Health & social care | 2016 |
| Athena Care Homes (Chesterton) Limited | Health & social care | 2023 |
| Athena Care Homes (March) Limited | Health & social care | 2015 |
| Atjm Consulting Limited | Construction | 2021 |
| ATK Property Maintenance Ltd | Administrative & support | 2025 |
| Atlantic Pacific Global Logistics Limited | Transport & logistics | 2000 |
| Atlantis Tues Belle Limited | Wholesale & retail | 2025 |
| Atlas Financial Advisory Ltd | Professional & scientific | 2026 |
| Atlas Property Solutions Ltd | Construction | 2025 |
| Atlas Staffing UK Ltd | Administrative & support | 2025 |
| Atlas Transport Services Limited | Transport & logistics | 2025 |
| Atlas Waste Ltd | Water & waste | 2020 |
| Atlas Waste Solutions Ltd | Water & waste | 2025 |
| Atlis Solutions Ltd | Information & communication | 2017 |
| ATM Pipework Fabrication Limited | Construction | 2014 |
| Atman TJ Limited | Construction | 2023 |
| Atnahs Pharma UK Limited | Manufacturing | 2013 |
| Atnahs Pharma US Limited | Manufacturing | 2016 |
| Atol Passive Fire Group Ltd | Construction | 2026 |
| Atomic Alloys Limited | Other services | 2019 |
| Atrefa Co Ltd | Health & social care | 2025 |
| Atromin Limited | Arts & recreation | 1985 |
| Atsams Consultant Limited | Information & communication | 2025 |
| Attic Cards Ltd | Wholesale & retail | 2026 |
| Atwal Chip Shop Long Riding Ltd | Hospitality | 2015 |
| Atwal Chip Shop Ltd | Hospitality | 2014 |
| Audio Native Limited | Professional & scientific | 2013 |
| Audley Educational Consultancy Limited | Education | 2014 |
| Audley Wealth Limited | Other services | 2020 |
| Augusty Properties Limited | Real estate | 2000 |
| Aumbry Services Limited | Other services | 2012 |
| Aumida Ltd | Other services | 2018 |
| Aura AB Ltd | Wholesale & retail | 2025 |
| Aura Electrical Southern Limited | Construction | 2017 |
| Auracity Ltd | Wholesale & retail | 2025 |
| Aurastral Ltd | Information & communication | 2025 |
| Aurelia Lange Illustration Ltd | Professional & scientific | 2019 |
| Auris Services Limited | Construction | 2015 |
| Aurora Chroma Ltd | Information & communication | 2026 |
| Aurora Impex Limited | Wholesale & retail | 2025 |
| Aurora UK Group Ltd | Construction | 2018 |
| Aurum Garden Rooms Ltd | Construction | 2025 |
| Aurumis Limited | Hospitality | 2025 |
| Austin Carroll Consultancy Limited | Professional & scientific | 2018 |
| Authentique Bakery Ltd | Hospitality | 2017 |
| Authorised Auto Locksmith Ltd | Administrative & support | 2026 |
| Auto Communications Ltd | Wholesale & retail | 2020 |
| Auto Express Vehicle Rental Limited | Transport & logistics | 1996 |
| Auto Go Trans Ltd | Transport & logistics | 2025 |
| Autocare PVT Ltd | Health & social care | 2014 |
| Autoenterprises Limited | Wholesale & retail | 2004 |
| Autohire(S & J)Limited | Wholesale & retail | 2004 |
| AUTOM8IQ Ltd | Professional & scientific | 2018 |
| Automech Consultant Ltd. | Information & communication | 2014 |
| Autoprofi Ltd | Wholesale & retail | 2024 |
| Autotax Limited | Administrative & support | 2018 |
| Autotek Technologies Ltd | Professional & scientific | 2024 |
| Autoventa Motors Limited | Wholesale & retail | 2024 |
| Autovoice UK Ltd | Information & communication | 2006 |
| Autoworks (Benfleet) Ltd | Wholesale & retail | 2015 |
| AV Indoors Ltd | Construction | 2022 |
| AV Niche (Recording Systems) Limited | Manufacturing | 1995 |
| AV Style Limited | Information & communication | 2019 |
| AV Vans Ltd | Wholesale & retail | 2026 |
| Avak Construction Ltd | Construction | 2023 |
| Avanet Services Ltd | Information & communication | 2026 |
| Avantgarde Tiling Limited | Construction | 2005 |
| Avar TM Ltd | Construction | 2024 |
| AVC Solar Ltd | Energy | 2023 |
| Avenue Interiors Ltd | Construction | 2023 |
| Aviary Developments Ltd | Construction | 2021 |
| Aviation Accountancy International Limited | Professional & scientific | 2024 |
| Avighna IT Consultancy Services Limited | Information & communication | 2024 |