| Advance Nutrition Limited | Health & social care | 2011 |
| Advance Services and Solutions Limited | Information & communication | 2004 |
| Advance Traffic Systems Ltd | Transport & logistics | 2024 |
| Advance Windows Ltd | Construction | 2010 |
| Advanced Aesthetics Reading Ltd | Health & social care | 2015 |
| Advanced Computer Technology Systems Limited | Information & communication | 2003 |
| Advanced Document Solutions Limited | Professional & scientific | 1998 |
| Advanced Layout Solutions Limited | Professional & scientific | 1995 |
| Advanced Maintenance Lettings Limited | Real estate | 2021 |
| Advanced Maintenance UK Limited | Construction | 1998 |
| Advanced Packing Solutions Limited | Administrative & support | 2006 |
| Advanced Tactical Resources Limited | Professional & scientific | 2012 |
| Advanced Tech Roofing Limited | Construction | 2020 |
| Advancedit-Services Ltd | Other services | 2012 |
| Adventis Properties Ltd | Households | 2024 |
| Adventure Development Limited | Real estate | 2024 |
| Adventure Finance Investments Limited | Professional & scientific | 2011 |
| Adventure Finance Limited | Professional & scientific | 2001 |
| Adventure Learning Childcare Limited | Education | 2013 |
| Adversio Group Limited | Financial services | 2024 |
| Advice & Coaching Partners Ltd | Professional & scientific | 2020 |
| Advicia Consulting Limited | Professional & scientific | 2003 |
| Advin Solutions Ltd | Wholesale & retail | 2024 |
| Advk Limited | Information & communication | 2021 |
| Advocate Marketing Ltd | Professional & scientific | 2015 |
| Advoco Solutions Limited | Administrative & support | 2007 |
| Adzz Properties Ltd | Real estate | 2025 |
| AE Food & Drinks Limited | Hospitality | 2026 |
| AE4 Studios Ltd | Manufacturing | 2025 |
| AEB Social Care Limited | Health & social care | 2015 |
| Aecom Technology Corporation Limited | Professional & scientific | 2025 |
| Aecoz Limited | Wholesale & retail | 2025 |
| AEG Developments Ltd | Construction | 2018 |
| Aegean Group Ltd | Construction | 2023 |
| Aegletes III Holdco Limited | Administrative & support | 2021 |
| AEL Outdoor Solutions Limited | Extraterritorial | 2015 |
| AEL Solutions Limited | Extraterritorial | 2015 |
| Aema Global Ltd | Wholesale & retail | 2026 |
| Aeonvista Limited | Information & communication | 2007 |
| Aequl Ltd | Professional & scientific | 2025 |
| Aerial Surveying Services Limited | Professional & scientific | 2015 |
| Aeris Communications Limited | Information & communication | 2013 |
| Aerocomponents Limited | Manufacturing | 1997 |
| Aerogel UK Limited | Construction | 2013 |
| Aerolight Electrical Limited | Manufacturing | 2023 |
| Aerospace Metallic Supply Limited | Wholesale & retail | 2009 |
| Aerotech, Limited | Manufacturing | 1981 |
| AES Holdco Limited | Financial services | 2025 |
| Aesir Systems Limited | Information & communication | 2026 |
| Aesthetic Home Improvements Ltd | Construction | 2017 |
| Aestimo Accounting Ltd | Professional & scientific | 2018 |
| Aethel Advisory Limited | Information & communication | 2026 |
| Aethelgard Solutions Limited | Professional & scientific | 2026 |
| Aether Maritime Ltd | Education | 2025 |
| Aetion UK Ltd | Professional & scientific | 2015 |
| Aetrix Group Limited | Wholesale & retail | 2024 |
| Aev.Gls Ltd | Transport & logistics | 2025 |
| AF Racing Limited | Administrative & support | 2025 |
| AFB Psychology Ltd | Education | 2023 |
| Afenssol Ltd | Professional & scientific | 2019 |
| Affaire DE Coeur Music Limited | Arts & recreation | 2003 |
| Affi Services Ltd | Wholesale & retail | 2020 |
| Affpraisal Limited | Professional & scientific | 2019 |
| Afghan Palace Reading Ltd | Hospitality | 2025 |
| AFM Group Limited | Arts & recreation | 1987 |
| AFN Limited | Professional & scientific | 1987 |
| AFP Holdings Limited | Financial services | 1993 |
| Afribean Links Co Ltd | Wholesale & retail | 2024 |
| African Pride Reading Limited | Wholesale & retail | 2019 |
| Africat UK | Other services | 2006 |
| Afrikmoney Ltd | Financial services | 2020 |
| Afripower LLP | | 2005 |
| Afro Crown Hair Limited | Wholesale & retail | 2020 |
| AFS Publishing Ltd | Arts & recreation | 2020 |
| AFS Wellbeing Ltd | Health & social care | 2025 |
| Afsang Advisory Associates 1 Ltd | Professional & scientific | 2022 |
| Aft.Guerin Ltd | Real estate | 2021 |
| Aftaw Ltd | Public administration | 2018 |
| Aftel Computers Limited | Real estate | 1994 |
| After Hours Accountants Ltd | Professional & scientific | 2024 |
| After Hours Decorating Limited | Construction | 2025 |
| AG Accountant Ltd | Professional & scientific | 2018 |
| AG Autotech Tadley Ltd | Wholesale & retail | 2021 |
| AG Unitec Ltd | Information & communication | 2017 |
| AG47 Energy Services Ltd | Construction | 2024 |
| Agamdeep Construction Limited | Construction | 2023 |
| Aganeyan Limited | Information & communication | 2012 |
| Agape Multi Academy Trust | Education | 2011 |
| Agaram Properties Ltd | Real estate | 2017 |
| Agata Inventio Ltd | Information & communication | 2025 |
| AGE Analytics Group Ltd | Information & communication | 2016 |
| AGE UK Berkshire | Health & social care | 2012 |
| Agenix Intelligence Ltd | Information & communication | 2025 |
| Agent Nine Ltd | Professional & scientific | 2025 |
| Agentaya Ltd | Information & communication | 2025 |
| Agentic Workforce Solutions Limited | Information & communication | 2018 |
| Agentix.Cx Ltd | Information & communication | 2026 |
| Agep Ltd | Education | 2025 |
| Agervirius Advisory Limited | Education | 2016 |
| Agex Consulting Limited | Information & communication | 1998 |