| Acorn Excavations Limited | Construction | 1997 |
| Acorn Steps Limited | Health & social care | 2025 |
| Acorns Day Nursery Limited | Education | 2002 |
| ACP ALL Clean Plus Ltd | Administrative & support | 2016 |
| Acre PAY Limited | Financial services | 2019 |
| Acroatics Limited | Information & communication | 2002 |
| Acros Pharma Services Limited | Professional & scientific | 2013 |
| ACS Accounting (Berkshire) Limited | Professional & scientific | 2004 |
| ACS Accounting Services Limited | Extraterritorial | 2004 |
| ACS Company Secretaries Limited | Extraterritorial | 2008 |
| Action Artists Agency Ltd | Administrative & support | 2021 |
| Active Movement Limited | Health & social care | 2013 |
| Active Plumbing & Heating Berkshire Ltd | Construction | 2014 |
| Activity Box Limited | Administrative & support | 2002 |
| Actual Consultancy Ltd | Professional & scientific | 2014 |
| Actual Consulting Ltd | Extraterritorial | 2014 |
| Actuarial Apps Limited | Information & communication | 2015 |
| Acuity Systems Limited | Information & communication | 2012 |
| Ad-Agm Limited | Information & communication | 2020 |
| Adams Haus Limited | Wholesale & retail | 2026 |
| Adeptai Consulting Limited | Information & communication | 2024 |
| Adnare Ltd | Information & communication | 2007 |
| ADP Property Management Ltd | Real estate | 2018 |
| Adra Tech Ltd | Information & communication | 2024 |
| Adrian Chesterman Ltd | Arts & recreation | 2024 |
| Adrian Landscaping & Property Services Ltd | Administrative & support | 2026 |
| Adrian Nita Limited | Administrative & support | 2022 |
| Adsj Associates Limited | Professional & scientific | 2004 |
| Advanced Aftersales Solutions Ltd | Wholesale & retail | 2019 |
| Advanced Design Build and Management Ltd | Construction | 2019 |
| Advanced Digital Consulting and Transformation Ltd | Information & communication | 2011 |
| Advanced Power and Cooling Limited | Wholesale & retail | 2018 |
| Advanced Realtime Cargo Technologies Ltd | Professional & scientific | 2009 |
| Advanced Support UK Ltd | Health & social care | 2015 |
| Advansys Group Limited | Professional & scientific | 2013 |
| Advansys Limited | Information & communication | 2000 |
| Advantage Smollan 2 Limited | Professional & scientific | 2025 |
| Advantage Smollan 3 Limited | Professional & scientific | 2026 |
| Advantage Smollan Limited | Professional & scientific | 2015 |
| Advica Holdings Limited | Energy | 2016 |
| Aegis Software Limited | Information & communication | 1999 |
| Aeroash Ltd | Information & communication | 2019 |
| AES Holdings Limited | Financial services | 2025 |
| Aesk Consulting LLP | | 2026 |
| Aether Devices UK Ltd | Manufacturing | 2025 |
| Aether Experience LLP | | 2024 |
| Affective Mobility Ltd | Professional & scientific | 2025 |
| Affluent Technologies Limited | Information & communication | 2019 |
| Afftech Services PVT Ltd | Information & communication | 2025 |
| Africhange Ltd | Professional & scientific | 2021 |
| Afrosaxon Limited | Professional & scientific | 2019 |
| Afternoon Paws Ltd | Manufacturing | 2019 |
| Agansiv Lettings Ltd | Real estate | 2023 |
| Agansiv Limited | Information & communication | 2011 |
| Agarwal Holdings Ltd | Real estate | 2020 |
| Agent 96 Limited | Information & communication | 2023 |
| Aghora Ltd | Real estate | 2019 |
| AGI Health Ltd | Information & communication | 2023 |
| Agile Cloud Technologies Ltd | Information & communication | 2023 |
| Agilis Regulatory Services Limited | Professional & scientific | 2023 |
| Agiliteq Ltd | Professional & scientific | 2021 |
| AH Home Solutions Limited | Construction | 2021 |
| Ahead UK Solutions Limited | Information & communication | 2019 |
| AI Building Services Ltd | Construction | 2024 |
| AI Compatible Ltd | Information & communication | 2023 |
| AI Control Tower Ltd | Administrative & support | 2025 |
| AI Imagine Limited | Information & communication | 2025 |
| AIM Property Developers Limited | Real estate | 2016 |
| Aipero Ltd | Education | 2024 |
| AIRCRAFT101 Ltd | Wholesale & retail | 2023 |
| Airspeed Limited | Wholesale & retail | 2006 |
| Aissured Ltd | Information & communication | 2026 |
| Aivero Technologies Limited | Information & communication | 2025 |
| Aivion Limited | Information & communication | 2024 |
| AJ Ward Ltd | Professional & scientific | 2026 |
| AJF Heat Pumps Ltd | Construction | 2024 |
| Ajmc Ltd | Information & communication | 2017 |
| Ajmc Property Limited | Real estate | 2025 |
| Ajoys Tech Ltd | Information & communication | 2021 |
| AK Coaching & Development Ltd | Other services | 2023 |
| Akaal Consulting Ltd | Information & communication | 2013 |
| Akka Group Ltd | Information & communication | 2026 |
| Akopong Ltd | Real estate | 2018 |
| Al-Barakah Services Ltd | Real estate | 2019 |
| Al-Brit Construction Ltd | Construction | 2020 |
| Alacran Group Ltd | Information & communication | 2018 |
| Alacran International Ltd | Information & communication | 2020 |
| Alan Reynolds & Company Limited | Professional & scientific | 1983 |
| Alandscapes Limited | Arts & recreation | 2006 |
| Alara’S Aesthetic’S Limited | Other services | 2021 |
| Albert Lovell Ltd. | Administrative & support | 2006 |
| Albion Global Consulting LLP | | 2025 |
| Alcapea Group LLP | | 2025 |
| Alex Nguyen Ltd | Other services | 2024 |
| Alexandra House (Reading) Management Company Limited | Households | 2004 |
| Alextonia Limited | Wholesale & retail | 2022 |
| Alfano Medics Ltd | Health & social care | 2020 |
| Alfor Fire Safety Services Limited | Administrative & support | 2011 |
| Alford Jones Limited | Professional & scientific | 2023 |
| Algiz Scaffolding Ltd | Construction | 2024 |