| Adam Faulkner Limited | Arts & recreation | 2014 |
| Adam K Contractors Limited | Construction | 2015 |
| Adam Luker Holdings Ltd | Real estate | 2023 |
| Adam Luker Limited | Real estate | 2020 |
| Adapt Healthservices Ltd | Professional & scientific | 2017 |
| Adaptive Fitness Ltd | Arts & recreation | 2025 |
| Adaptive Living Limited | Health & social care | 2017 |
| Adaptive Swarm Limited | Information & communication | 2026 |
| Adbrad Ltd | Information & communication | 2021 |
| ADC Communications (UK) Ltd. | Extraterritorial | 1978 |
| Adcdlv LLP | | 2023 |
| Adda Ecom Ltd | Wholesale & retail | 2024 |
| Addai Services Ltd | Health & social care | 2019 |
| Addalogouk Limited | Manufacturing | 2024 |
| Addis Project Management Ltd | Administrative & support | 2012 |
| Addsam Creations Limited | Wholesale & retail | 2017 |
| Adelaja & Partners Family Inc Ltd | Households | 2025 |
| Adept Air Ltd | Professional & scientific | 2026 |
| Adept Networks Ltd | Wholesale & retail | 2004 |
| Adesant Ltd | Information & communication | 2020 |
| Adest Limited | Real estate | 2023 |
| Adhere Healthcare Ltd | Health & social care | 2019 |
| ADI Serv Ltd | Transport & logistics | 2015 |
| ADK Contractors Limited | Construction | 2017 |
| Adkk Ltd | Wholesale & retail | 2025 |
| Admin Business Services Limited | | 1986 |
| Adminiy Ltd | Administrative & support | 2012 |
| Admirantis Limited | Real estate | 2015 |
| Adoa Limited | Real estate | 2022 |
| Adom Care Swindon Ltd | Health & social care | 2022 |
| Adrc Consultants Ltd | Administrative & support | 2024 |
| Adrian AI Technologies Limited | Information & communication | 2024 |
| Adrian Digby Ltd | Professional & scientific | 2023 |
| Adroit Builders (Wiltshire) Ltd | Construction | 2012 |
| Adstral Limited | Administrative & support | 2010 |
| Advanced Dental Limited | Health & social care | 2016 |
| Advanced Electric Powertrain Solutions Limited | Professional & scientific | 2024 |
| Advanced Measuring Systems Ltd | Administrative & support | 2015 |
| Advanced Printing Services (UK) Limited | Manufacturing | 2000 |
| Advanced Product Delivery Limited | Professional & scientific | 2015 |
| Advanced Vehicle Movers Ltd | Transport & logistics | 2023 |
| Adventure Golf (Oxford) Limited | Arts & recreation | 2017 |
| Adventurine Limited | Administrative & support | 2003 |
| Advertising, Design and Print Limited | Arts & recreation | 2003 |
| Advice on Wealth Ltd | Professional & scientific | 2005 |
| Advise My Finances Ltd | Professional & scientific | 2022 |
| Advocacy After Fatal Domestic Abuse Ltd | Health & social care | 2015 |
| Advocation Limited | Information & communication | 1997 |
| Advtec Ltd | Information & communication | 2006 |
| AE Campbell Ltd | Real estate | 2013 |
| AE Investments-Uk Limited | Real estate | 2024 |
| AE Robinson Limited | Real estate | 2023 |
| AEC Electrical Services Limited | Construction | 2007 |
| AEG (UK) Ltd | Administrative & support | 2008 |
| Aegis Marketing Solutions Ltd | Wholesale & retail | 2024 |
| Aegis Rose Ltd | Information & communication | 2024 |
| AEM ALI Ltd | Wholesale & retail | 2025 |
| Aerial Target Systems Limited | Other services | 1994 |
| Aeromotive Design Ltd | Construction | 1998 |
| Aeropro Limited | Information & communication | 2008 |
| Aesthetics by SMC Ltd | Other services | 2023 |
| AF Trading Swindon Ltd | Wholesale & retail | 2024 |
| Affaible Ltd | Extraterritorial | 2024 |
| Affinity Rooms Limited | Other services | 2023 |
| Affleck Electrical Limited | Administrative & support | 2002 |
| Affleck Mechanical Services Limited | Administrative & support | 2009 |
| AFG Fast Food Ltd | Hospitality | 2023 |
| Afhm Transfers Ltd | Transport & logistics | 2025 |
| Afnor UK Limited | Administrative & support | 1992 |
| AFR Air Conditioning Limited | Construction | 2002 |
| African Fashion Allure Ltd | Wholesale & retail | 2018 |
| African Star Tours Ltd. | Administrative & support | 2016 |
| Afro Caribbean Store Limited | Wholesale & retail | 2017 |
| Afro Cuts 1 Barbershop Ltd | Other services | 2026 |
| Afro-Brit Centre for International Development | Education | 2025 |
| Afrorganic Food-House Ltd | Wholesale & retail | 2026 |
| Afterlife Golf Limited | Wholesale & retail | 2025 |
| Aftk Electrical Consultants Ltd | Construction | 2024 |
| AG Dental (Equipment) Limited | Professional & scientific | 2009 |
| AG Innovation Limited | Professional & scientific | 2014 |
| Ag&T Limited | Professional & scientific | 2015 |
| Agape Sanctuary Ltd | Health & social care | 2026 |
| Agar Media Ltd | Information & communication | 2024 |
| Ageless Group Limited | Professional & scientific | 2016 |
| Agent Adjacent Limited | Professional & scientific | 2014 |
| Agent Desk Ltd | Information & communication | 2026 |
| AGI Corporate Finance Limited | Administrative & support | 1996 |
| Agile Approach Ltd | Professional & scientific | 2009 |
| Agile IX Ltd | Information & communication | 2019 |
| Agile Rehab Limited | Health & social care | 2012 |
| Agile Terriers Limited | Professional & scientific | 2024 |
| Agilist Ltd | Information & communication | 2016 |
| Agnar Limited | Administrative & support | 2018 |
| Agnieszka Ordakowska Ltd | Professional & scientific | 2021 |
| Agnieszkatax Ltd | Professional & scientific | 2017 |
| AGO Meddent Ltd | Health & social care | 2021 |
| Agralan Limited | Agriculture & fishing | 1986 |
| Agribulk Limited | Transport & logistics | 1994 |
| Agricultural & Estate Services Limited | Construction | 2006 |
| Agro Greenshaw Limited | Agriculture & fishing | 2025 |