| Active Data Ltd | Professional & scientific | 2002 |
| Active Extract Cleaning Limited | Administrative & support | 2015 |
| Active Successful Engagement (ASE) CIC | Education | 2013 |
| Activia Enterprises Limited | Wholesale & retail | 2008 |
| Acton Holdings Limited | Financial services | 2021 |
| Acuative Limited | Information & communication | 1999 |
| AD Astra Childrens Services Ltd | Health & social care | 2024 |
| ADA Corporation Limited | Professional & scientific | 2012 |
| Adam Group Ltd | Construction | 2010 |
| Adam Props Ltd | Other services | 2023 |
| Adam Ridgeway Ltd | Administrative & support | 2023 |
| Adam Star Tech Ltd. | Information & communication | 2025 |
| Adam's Peak Limited | Administrative & support | 2013 |
| Adam's Traditional Barbers Limited | Other services | 2017 |
| Adams Fitness Ltd | Wholesale & retail | 2017 |
| Adams Pork Products Limited | Extraterritorial | 1969 |
| Adams Properties and Developments Limited | Construction | 2025 |
| Adamsway Services Limited | Professional & scientific | 2013 |
| Adan Estates Property Management Ltd | Real estate | 2018 |
| Adaptog Research Ltd | Wholesale & retail | 2026 |
| Addington House Limited | Health & social care | 2002 |
| Adequipt Ltd | Information & communication | 2018 |
| Adexchange Media Limited | Information & communication | 2001 |
| Adhk Accountants Limited | Professional & scientific | 2007 |
| Adhk Properties Limited | Real estate | 2014 |
| ADI Capitals Limited | Real estate | 2023 |
| Adiana UK Limited | Real estate | 2025 |
| Adil Vaqaas Ltd | Real estate | 2023 |
| ADK Cooling Limited | Hospitality | 2010 |
| ADM SB4 Limited | Health & social care | 2021 |
| Adman & Co Ltd | Professional & scientific | 2012 |
| Adora Construction Ltd | Manufacturing | 2021 |
| Adott IT Solutions Limited | Information & communication | 2022 |
| ADR Futures Limited | Real estate | 2025 |
| Adriot Accountants Ltd | Professional & scientific | 2012 |
| ADS Facades Ltd | Construction | 2023 |
| ADS Surveyors Ltd | Professional & scientific | 2025 |
| ADU After School Club Limited | Health & social care | 2026 |
| Advance Mortgages & Protection Ltd | Financial services | 2021 |
| Advance Property Preservation Limited | Construction | 1995 |
| Advance Psychology Ltd | Health & social care | 2021 |
| Advanced Business Equipment Limited | Administrative & support | 1991 |
| Advanced Business Solution House Limited | Information & communication | 2002 |
| Advanced Childcare Services Limited | Health & social care | 2011 |
| Advanced Clinical Consulting Ltd | Education | 2023 |
| Advanced Group Holdings Limited | Professional & scientific | 2016 |
| Advanced Oral Surgery and Implantology Limited | Health & social care | 2011 |
| Advanced Prototyping and Engineering Excellence Ltd | Information & communication | 2020 |
| Advanced Software Solutions Ltd | Information & communication | 2012 |
| Advanced Solutions Limited | Manufacturing | 1989 |
| Advanced Specialist Logistics Ltd | Transport & logistics | 2020 |
| Advances in Autism Care & Education Limited | Health & social care | 1996 |
| Advantage Odyssey Limited | Financial services | 2025 |
| Advantage Physiotherapy Limited | Health & social care | 2011 |
| Advantax Digital Ltd | Professional & scientific | 2018 |
| Advisory Plus Limited | Professional & scientific | 2012 |
| AE Design & Construction Ltd. | Construction | 2016 |
| AEI Air (Holdings) Limited | Professional & scientific | 2010 |
| AEI Systems Limited | Manufacturing | 2002 |
| AEK Property Ltd | Real estate | 2021 |
| Aelius Group Ltd | Administrative & support | 2022 |
| Aelius Ruislip Developments Limited | Real estate | 2023 |
| Aeman Builders Ltd | Construction | 2019 |
| Aemia UK Limited | Transport & logistics | 2007 |
| Aenw Ltd | Other services | 2024 |
| Aequitas Estates (Hertford) Limited | Real estate | 2021 |
| Aequitas Estates (Maidstone) Limited | Construction | 2014 |
| Aequitas Estates (Midlands NO.2) Limited | Real estate | 2017 |
| Aequitas Estates (Raunds) Limited | Real estate | 2016 |
| Aequitas Estates Holdings Limited | Financial services | 2017 |
| Aequitas Estates Limited | Real estate | 2013 |
| Aequitas Holdings Limited | Financial services | 2024 |
| Aequitate Ventures Limited | Financial services | 2021 |
| Aerial Drone & Helicopter Surveying Ltd | Professional & scientific | 2025 |
| Aeroair Ltd | Administrative & support | 1984 |
| Aeropick Airport Transport Limited | Transport & logistics | 2024 |
| Aeroride Ltd | Transport & logistics | 2024 |
| Aerospace Design Facilities Ltd | Professional & scientific | 2000 |
| Aeroxonic Ltd | Wholesale & retail | 2025 |
| Aervo Ltd | Arts & recreation | 2019 |
| Aesculap Limited | Health & social care | 2019 |
| Aesir Automotive Ltd | Wholesale & retail | 2020 |
| Aesn Care Limited | Health & social care | 2024 |
| Aesn Limited | Information & communication | 2019 |
| Aesn Travels & Tours Ltd | Administrative & support | 2025 |
| Aesthethically Ltd | Information & communication | 2014 |
| Aesthetic Construction Ltd | Construction | 2017 |
| Aesthetics Boutique Ltd | Wholesale & retail | 2021 |
| Aestheticus Group Limited | Wholesale & retail | 2015 |
| Aether Enterprises Ltd | Professional & scientific | 2025 |
| AF Wealth Management Ltd | Financial services | 2022 |
| Afbl Ltd | Professional & scientific | 2025 |
| Afendakis Ltd | Professional & scientific | 2026 |
| Affinity Financial Advisors Limited | Financial services | 2003 |
| Affinity Financial Holdings Limited | Financial services | 2020 |
| Affinity Green Limited | Administrative & support | 2022 |
| Affixx Ltd | Construction | 2024 |
| Affno Ltd | Construction | 2025 |
| Affordable Tech Limited | Information & communication | 2013 |
| Afghan Delights Ltd | Hospitality | 2025 |