| A1 Fire Doors Limited | Construction | 2024 |
| A1 Movable Walls Limited | Construction | 2014 |
| A10 CBS Ltd | Real estate | 2019 |
| A10 Roofing (London) Limited | Construction | 1999 |
| A12 CBS Limited | Real estate | 2022 |
| A130 CBS Limited | Real estate | 2022 |
| A1R Consultancy Limited | Professional & scientific | 2017 |
| A1R Consultancy Services Limited | Administrative & support | 2014 |
| A1R Services Limited | Administrative & support | 2006 |
| AA Properties (Essex) Ltd | Wholesale & retail | 2025 |
| Aaaw Developments Limited | Real estate | 2023 |
| Aardvark Consult Ltd | Real estate | 2018 |
| Aarhouze Limited | Transport & logistics | 2018 |
| Aaron Homes Lettings Limited | Real estate | 2017 |
| Abben Investments Limited | Real estate | 2015 |
| Abbey Cross Angling Society Limited | Arts & recreation | 2005 |
| Abbey Road (Barking) Management Limited | Households | 2007 |
| Abbey Tile Supplies Limited | Wholesale & retail | 2010 |
| Abbots Taxis Ltd | Transport & logistics | 2023 |
| Abdo Consulting Limited | Professional & scientific | 2008 |
| Abel Living Limited | Real estate | 2021 |
| Abel Living Management Limited | Construction | 2024 |
| Abel Smith Trustees (One) Limited | Professional & scientific | 2023 |
| Abel Smith Trustees (Two) Limited | Professional & scientific | 2023 |
| Abercorn Mansions Management Limited | Administrative & support | 2000 |
| Aberdeen House ( Pulborough ) Ltd | Real estate | 2023 |
| Aberdeen House (Lindford) Ltd | Real estate | 2022 |
| Above Consulting Ltd | Professional & scientific | 2015 |
| Abraham Hawkes Developments Limited | Real estate | 2020 |
| Abraham Hawkes Limited | Real estate | 2020 |
| ABT People Ltd | Professional & scientific | 2023 |
| AC Jigsaw Limited | Real estate | 2019 |
| AC Mortgage & Protection Solutions Limited | Financial services | 2022 |
| Acagrii&Dig Ltd | Agriculture & fishing | 2025 |
| Access Rail Civil Limited | Construction | 2024 |
| Access Scaffolding Limited | Construction | 2024 |
| Ace Studios Group Ltd | Administrative & support | 2026 |
| Ace Timber and Building Supplies Limited | Wholesale & retail | 2024 |
| ACE17 Development Limited | Construction | 2020 |
| Aces Weekly Limited | Arts & recreation | 2011 |
| Acre Cars Group Ltd | Transport & logistics | 2026 |
| Acreview Management Limited | Real estate | 2026 |
| ACS Investment (London) Limited | Other services | 2025 |
| ACS Projects (London) Limited | Manufacturing | 2019 |
| Acticare Limited | Professional & scientific | 2004 |
| Actin Time Ltd | Other services | 2009 |
| Action Electrics Limited | Manufacturing | 2014 |
| Active Construction Solutions Limited | Construction | 2009 |
| ACU Facial Limited | Health & social care | 2012 |
| Acumen Mechanical Electrical Construction Ltd | Construction | 2020 |
| AD Carpentry and Building (Hertford) Ltd | Construction | 2026 |
| AD Construction (Hertford) Ltd | Construction | 2026 |
| Adam Kennedy Broadcast Services Ltd | Information & communication | 2021 |
| Adapt and Exceed Ltd | Professional & scientific | 2021 |
| Adaptive Reasoning Ltd | Information & communication | 2010 |
| Addition Coaching Ltd | Health & social care | 2025 |
| Adim Plumbing Heating & Building Services Ltd | Construction | 2019 |
| ADS Designs Limited | Construction | 2021 |
| Advanced Health Solutions Limited | Wholesale & retail | 2005 |
| Advisor Trusts and Probate Services Ltd | Financial services | 2007 |
| AE Investment Holdings Ltd | Financial services | 2026 |
| AEA ST Johns Ltd | Real estate | 2025 |
| AEB Services Limited | Construction | 2019 |
| Aeon Green Limited | Information & communication | 2011 |
| Aeon Green Subsurface Limited | Administrative & support | 2011 |
| Aeris Elixers Ltd | Manufacturing | 2025 |
| Aesthetically Pleasing Limited | Construction | 2010 |
| Afermo Limited | Information & communication | 2017 |
| After Hours Fight Club Limited | Arts & recreation | 2025 |
| AGC Carpentry Limited | Manufacturing | 2020 |
| AGE UK Hertfordshire | Health & social care | 1998 |
| AGE UK Hertfordshire Trading Limited | Other services | 1994 |
| Agency a Limited | Professional & scientific | 2020 |
| Agency Ninety Ltd | Arts & recreation | 2007 |
| Aggmax Recycling Ltd | Administrative & support | 2022 |
| Aggri-Haul Group Ltd | Transport & logistics | 2024 |
| Agility PR Limited | Professional & scientific | 2003 |
| Agri-Supply UK Limited | Wholesale & retail | 2008 |
| Ahear Records Ltd | Manufacturing | 2022 |
| AI Martin & Co Ltd | Real estate | 2016 |
| Aidan Bede Ltd | Professional & scientific | 2019 |
| Aidan Mcclelland Limited | Construction | 1999 |
| Aigentiq UK Ltd | Professional & scientific | 2025 |
| Air Energy Limited | Other services | 2002 |
| Aircare Technology Ltd | Manufacturing | 2015 |
| Ajac Accumulation Ltd | Financial services | 2025 |
| Ajjiuk Enterprises Ltd | Wholesale & retail | 2018 |
| AJK Drawing Services Ltd | Administrative & support | 2010 |
| AJK Environmental Ltd | Construction | 2016 |
| AJK Woodflooring Ltd | Construction | 2000 |
| AK Property Investments Limited | Real estate | 2001 |
| AK Urban Properties Ltd | Real estate | 2024 |
| AL Appliances Ltd | Wholesale & retail | 2021 |
| AL Herron Limited | Hospitality | 2023 |
| AL Security Systems Ltd | Administrative & support | 2024 |
| Alafaire’S Coffee Ltd | Hospitality | 2023 |
| Alana Concepts Limited | Construction | 2003 |
| Alandra Products Limited | Wholesale & retail | 1975 |
| Alaska Commodities Ltd | Wholesale & retail | 2025 |
| Alaska Commodities Support Services Ltd. | Transport & logistics | 2025 |