| Aegir MSA Ltd | Information & communication | 2020 |
| Aegis Care Shield Ltd | Health & social care | 2024 |
| AER Collective Limited | Administrative & support | 2024 |
| Aercon Sheet Metalcraft Limited | Manufacturing | 1946 |
| Aerial Direct Limited | Information & communication | 2012 |
| Aerial Group Limited | Financial services | 2018 |
| Aerial Telephones Limited | Information & communication | 1994 |
| Aerial Wholesale Limited | Information & communication | 2022 |
| Aerofix Aviation Ltd | Manufacturing | 2026 |
| Aeromarine Ltd | Manufacturing | 2021 |
| Aeviam Ltd | Information & communication | 2026 |
| AFA Getaways Ltd | Administrative & support | 2023 |
| Affinity Developments Ltd | Construction | 2019 |
| Affluent Avenues Limited | Real estate | 2024 |
| Affordable Accounting Ltd | Professional & scientific | 2016 |
| Afri Trade Hub Ltd | Wholesale & retail | 2025 |
| African Nurses and Midwives Association UK Community Interest Company | Education | 2024 |
| Afterglow at 102 Ltd | Other services | 2025 |
| AFW Express Ltd | Transport & logistics | 2021 |
| AG Consultancy & Services Limited | Administrative & support | 2017 |
| AG Weld Services Ltd | Construction | 2024 |
| Agar DRY Mortar Holding Limited | Administrative & support | 1999 |
| AGG Holdings Limited | Real estate | 2016 |
| Agile Aviation Consultancy Limited | Professional & scientific | 2025 |
| Agile Network 360 Limited | Information & communication | 2017 |
| Agile Network International Limited | Information & communication | 2017 |
| Agile Network Systems Limited | Information & communication | 2016 |
| AGT Composites Ltd | Manufacturing | 2023 |
| Ah&Son Construction Ltd | Manufacturing | 2026 |
| Ahmad Property Ltd | Households | 2025 |
| Ahmazhara Limited | Professional & scientific | 2022 |
| AHN Property Services Limited | Construction | 2024 |
| AI Beauty Consultancy Ltd | Administrative & support | 2018 |
| AI Beauty Group Ltd | Financial services | 2018 |
| AI Bioengineering Solutions Ltd | Information & communication | 2025 |
| AI Russell Limited | Professional & scientific | 2025 |
| Ai-On Technology Limited | Information & communication | 2026 |
| AIA Wallop Defence Ltd | Public administration | 2024 |
| Aidc Solutions Limited | Administrative & support | 2004 |
| Aifurbo Limited | Wholesale & retail | 2025 |
| Aigentic Solutions Ltd | Information & communication | 2025 |
| Ailstructural Ltd | Professional & scientific | 2018 |
| AIM Copier Supplies Limited | Administrative & support | 2020 |
| AIM Homecare Limited | Health & social care | 2017 |
| Ainslieco Limited | Financial services | 2023 |
| Air Care Services (Fareham) Limited | Construction | 2007 |
| Air Quality Plan Ltd | Professional & scientific | 2013 |
| Airborne Electrical Ltd | Construction | 2019 |
| Airdrie Specsavers Limited | Wholesale & retail | 2008 |
| Airdrie Visionplus Limited | Wholesale & retail | 2008 |
| Airport Engineering Solutions Limited | Information & communication | 2021 |
| Airport Facilities (Heathrow) Limited | Construction | 2014 |
| Airport Facilities (Maintenance) Limited | Construction | 2009 |
| Airtech Extraction Ltd | Construction | 2023 |
| Airways Optical Limited | Manufacturing | 1994 |
| Airzone Events Limited | Hospitality | 1999 |
| AJ (Propco) South Limited | Construction | 2022 |
| AJ Creative Builders Ltd | Construction | 2026 |
| AJ Fraser Services Limited | Energy | 2007 |
| AJ Gold Jeweller Ltd | Wholesale & retail | 2025 |
| AJ Handlers Ltd | Transport & logistics | 2020 |
| AJ Lington Ltd | Wholesale & retail | 2006 |
| AJG Engineering Solutions Ltd | Professional & scientific | 2019 |
| AJP Diagnostics Limited | Health & social care | 2015 |
| AJP Property Solutions Ltd | Real estate | 2020 |
| Ajssbcynsm Limited | Wholesale & retail | 2025 |
| AJW Property Group Ltd | Professional & scientific | 2011 |
| AJW77 Limited | Manufacturing | 2022 |
| Ajwebcommerce Ltd | Wholesale & retail | 2022 |
| Ak-U-Rite (UK) Limited | Manufacturing | 2000 |
| Akhal Properties Ltd | Real estate | 2026 |
| AKO Carpentry & Building Limited | Construction | 2019 |
| Akse Limited | Other services | 2015 |
| Aksh Property Ltd | Real estate | 2025 |
| Akumar Enterprises Limited | Financial services | 2024 |
| Akwafoods Ltd | Wholesale & retail | 2025 |
| AL and Sons Wheels Limited | Other services | 2013 |
| AL Mahdi Centre | Other services | 2009 |
| AL Project Consultants Ltd | Professional & scientific | 2025 |
| AL PVT Ltd | Health & social care | 2025 |
| Al-Bukhaari Limited | Wholesale & retail | 2024 |
| Alacritas Innovations Limited | Wholesale & retail | 2021 |
| Alami Trading Ltd | Wholesale & retail | 2025 |
| Alan a. Griffin Associates UK Limited | Professional & scientific | 1995 |
| Alan Brind Tree Services Ltd | Agriculture & fishing | 2010 |
| Alan Estate Limited | Hospitality | 2006 |
| Alan Heard Engineering Ltd | Professional & scientific | 2013 |
| Alan J Rose Limited | Hospitality | 2010 |
| Alan Woodcock Limited | Wholesale & retail | 1946 |
| Alarmis Security Systems Limited | Administrative & support | 2006 |
| Alatar Ltd | Professional & scientific | 2023 |
| Albany Care (Northampton) Limited | Health & social care | 2016 |
| Albany Care (Portchester) Ltd | Other services | 2019 |
| Albany Care Properties (Milton) Limited | Other services | 2019 |
| Albany Day Care Limited | Other services | 2021 |
| Albany DOM Care Limited | Other services | 2021 |
| Albany Farm Care (Hampshire) Limited | Health & social care | 2013 |
| Albany Farm Care (Havant) Limited | Other services | 2016 |
| Albany Farm Care (Oxford) Limited | Other services | 2016 |
| Albany Group Holdings Ltd | Other services | 2016 |