| ACS Aircon Services (South East) Limited | Construction | 2013 |
| Action Coaching Limited | Wholesale & retail | 2016 |
| Action for Deafness | Health & social care | 2007 |
| Active House Ltd. | Professional & scientific | 2011 |
| Activeled Ltd | Extraterritorial | 2005 |
| Actomac Ltd | Professional & scientific | 2023 |
| Acumen Portfolio Solutions Limited | Professional & scientific | 2009 |
| AD Matocha Limited | Administrative & support | 2015 |
| Adam Barker Limited | Financial services | 2017 |
| Adam Birley Consulting Ltd | Professional & scientific | 2024 |
| Adam Durrant Ltd | Information & communication | 2021 |
| Adams & Barker Limited | Construction | 1992 |
| Adams and Booker Ltd | Real estate | 2025 |
| Addison Clark Search Limited | Professional & scientific | 2022 |
| Adelaide Healthcare Limited | Health & social care | 2007 |
| Adelphi (Tubes) Limited | Wholesale & retail | 1970 |
| Adelphi Holdings Limited | Financial services | 1999 |
| Adelphi Manufacturing Company,Limited | Manufacturing | 1947 |
| Adelphi Masterfil Limited | Manufacturing | 2007 |
| Aditi Edhas Ltd | Professional & scientific | 2020 |
| Adler Aesthetics & Beauty Limited | Other services | 2025 |
| ADM Sports Consultants Limited | Professional & scientific | 2014 |
| Admin AI Ltd | Information & communication | 2026 |
| Adminity Limited | Administrative & support | 2025 |
| Adored App Ltd | Information & communication | 2025 |
| Adoreum Group Limited | Professional & scientific | 2007 |
| Adoreum Holdings Limited | Financial services | 2020 |
| Adoreum Ltd | Wholesale & retail | 2004 |
| Adoreum Partners Ltd | Professional & scientific | 2009 |
| Adoreus Limited | Professional & scientific | 2017 |
| ADP Plumbing & Property Services Limited | Construction | 2022 |
| ADR Southern Property Group Ltd | Real estate | 2025 |
| Adrian Powell Creative Limited | Professional & scientific | 2025 |
| Adur 2022 Company | Financial services | 2023 |
| Advance Care Solutions Ltd | Health & social care | 2022 |
| Advance Jewels Ltd | Manufacturing | 2022 |
| Advanced Marketing Intelligence Ltd | Information & communication | 2024 |
| Advantage Cloud Solutions Ltd | Professional & scientific | 2015 |
| Adventrix Ltd | Manufacturing | 2024 |
| Advercheck Ltd | Professional & scientific | 2020 |
| Advice Firm Compliance Ltd | Professional & scientific | 2024 |
| ADZ Securtiy Limited | Administrative & support | 2025 |
| Aegis Rubber Engineering Limited | Manufacturing | 1992 |
| Aelana Estates Limited | Real estate | 2025 |
| AEM Electrical Contracting Ltd | Construction | 2021 |
| Aequa Mundi Ltd | Construction | 2024 |
| Aeration Innovations Ltd | Professional & scientific | 2026 |
| Aerospace Research and Consulting Ltd | Professional & scientific | 2014 |
| Aerovex Ltd | Agriculture & fishing | 2026 |
| Aesthetics by Debbie Ltd | Health & social care | 2024 |
| AFC Contracting Limited | Construction | 2013 |
| AFC Distribution Limited | Transport & logistics | 2013 |
| AFK & Associates Limited | Administrative & support | 2012 |
| Afobi Limited | Real estate | 2012 |
| African Writers Abroad CIC | Education | 2023 |
| AG Drylining & Interiors Ltd | Construction | 2023 |
| Agave New Ventures Ltd | Information & communication | 2025 |
| Ager Build - Ltd | Construction | 2018 |
| Ager Solutions Ltd | Extraterritorial | 2017 |
| Agnes and Lola Ltd | Wholesale & retail | 2018 |
| Agnes Care Ltd | Health & social care | 2015 |
| AH IT Tech Ltd | Information & communication | 2022 |
| AHK Medical Ltd | Health & social care | 2022 |
| AHK Regal Ltd | Real estate | 2019 |
| AHS Advisory Services Ltd | Professional & scientific | 2024 |
| AHS Nice Work Ltd | Arts & recreation | 2020 |
| AHS Wellbeing Online CIC | Administrative & support | 2020 |
| Air CON Solutions Ltd | Construction | 2019 |
| Air-Britain (Events) Ltd | Arts & recreation | 1983 |
| Air-Britain (Trading) Limited | Information & communication | 2015 |
| Airacro Gymnastics Ltd | Arts & recreation | 2025 |
| Airs Productions Limited | Professional & scientific | 2025 |
| AJF Pet Marketing Ltd | Professional & scientific | 2023 |
| AK and Sims Limited | Health & social care | 2022 |
| Akatsuki Medical Ltd | Health & social care | 2023 |
| Akehurst Group Ltd | Construction | 2016 |
| Akehurst Heating & Renewables Limited | Construction | 2023 |
| Akehurst Holdings Ltd | Financial services | 2023 |
| Akei Investment Limited | Real estate | 2018 |
| AKI Air Ltd | Construction | 2017 |
| AKL Laser Clinic Ltd | Health & social care | 2025 |
| Akos BIO Ltd | Wholesale & retail | 2024 |
| AL Camino Company Ltd | Professional & scientific | 2024 |
| Alan Compton Film & Photography Limited | Information & communication | 2013 |
| Alan Hill & Co Ltd | Professional & scientific | 2011 |
| Alan Robinson (Sussex) Limited | Financial services | 2014 |
| Albany Property & Capital Limited | Real estate | 2014 |
| Albert Ross Investments Limited | Real estate | 2014 |
| Albi Finance Limited | Financial services | 2026 |
| Aldene Management Limited | Real estate | 2009 |
| Alder Corporation Limited | Administrative & support | 2022 |
| Alderstrom Limited | Information & communication | 2016 |
| Alegan Development Ltd | Real estate | 2024 |
| Alexander Construction Services Ltd | Construction | 2017 |
| Alexander Mcqueen Trading Limited | Administrative & support | 2002 |
| Alexander Samson Consulting Limited | Professional & scientific | 2019 |
| Alexandra Carello Consulting Limited | Administrative & support | 2019 |
| Alfred Manchester & Sons Ltd | Transport & logistics | 2009 |
| Algostim Research and Development Ltd | Manufacturing | 2023 |
| Alice Henderson Limited | Wholesale & retail | 2014 |