| Aclarius Limited | Professional & scientific | 2020 |
| ACM Property Renovations Ltd | Construction | 2023 |
| ACN Commercial Services Ltd | Administrative & support | 2022 |
| Acorn Commercial Valeting Limited | Administrative & support | 2004 |
| Acorn Kitchens & Bathrooms Ltd | Construction | 2009 |
| Acorn Professional Property Investment Ltd | Real estate | 2020 |
| Acorn Solutions Ltd | Wholesale & retail | 2018 |
| Acorn Tyres (Aylesbury) Ltd | Wholesale & retail | 2013 |
| ACR Driving Services Limited | Transport & logistics | 2025 |
| Acre Lettings and Properties Ltd | Real estate | 2020 |
| Acrity Limited | Professional & scientific | 2013 |
| Across the Line Ltd | Professional & scientific | 2023 |
| Across the Miles Limited | Extraterritorial | 2020 |
| ACS Compressed Air Technology Ltd. | Manufacturing | 2011 |
| ACS Trustee 1 Ltd | Arts & recreation | 2024 |
| ACS Trustee 2 Ltd | Arts & recreation | 2024 |
| ACS12 UK Ltd | Education | 2024 |
| ACT Retail Solutions Ltd | Professional & scientific | 2017 |
| Action Force Business Improvement Ltd | Professional & scientific | 2025 |
| Action Locksmiths Limited | Other services | 2024 |
| Action Property 76 Limited | Real estate | 2026 |
| ACTION4YOUTH | Education | 1994 |
| Active in the Community C.I.C. | Professional & scientific | 2017 |
| Activelifepelvichealth Limited | Health & social care | 2025 |
| Activideas Limited | Real estate | 2002 |
| Acubuild Solution Ltd | Construction | 2015 |
| Acutance Insights Ltd | Information & communication | 2023 |
| Acvc ALL Catering Van Conversions Ltd | Wholesale & retail | 2021 |
| AD Global Partners Ltd | Administrative & support | 2018 |
| AD Security Solutions Limited | Administrative & support | 2016 |
| Ad&C Ltd | Administrative & support | 2023 |
| Adage Music Limited | Information & communication | 2006 |
| Adams Brothers Limited | Wholesale & retail | 1971 |
| Adams Garage Aylesbury | Extraterritorial | 1947 |
| Adams Garage Limited | Extraterritorial | 1984 |
| Adams Plumbing & Construction Ltd | Construction | 2019 |
| Adams Travel Agency Limited | Administrative & support | 2022 |
| Adamsky Adam Ltd | Construction | 2019 |
| Adan Construction Ltd | Construction | 2024 |
| Adaptar Consulting Ltd | Administrative & support | 2010 |
| Adashvik Ltd | Professional & scientific | 2023 |
| ADB One Ltd | Professional & scientific | 2019 |
| ADDICTED2ADVENTURES Ltd | Administrative & support | 2018 |
| Addison Court Chesham Company Limited | Households | 2015 |
| Addison Plus Ltd | Administrative & support | 2014 |
| Adek Rigging and Scaffolding Services Limited | Construction | 2022 |
| Adellco Ltd | Professional & scientific | 2007 |
| Adept Interiors Limited | Construction | 2016 |
| Adeptsys Limited | Information & communication | 2007 |
| Adhd HER Ltd | Administrative & support | 2024 |
| Adhithi Ltd | Information & communication | 2022 |
| Adhyapak Ltd | Education | 2025 |
| ADI3 Ltd | Wholesale & retail | 2025 |
| Aditi Courier Ltd | Transport & logistics | 2023 |
| Admiah Digital Ltd | Professional & scientific | 2020 |
| ADN Advisory Limited | Financial services | 2016 |
| Adobe Services Limited | Administrative & support | 2016 |
| Adonai Rapha Limited | Professional & scientific | 2014 |
| Adore Labs Ltd | Wholesale & retail | 2026 |
| Adore Nail & Beauty Ltd | Other services | 2024 |
| Adorr Consultancy Ltd | Real estate | 2026 |
| Adpro Solutions Ltd | Professional & scientific | 2025 |
| Adpt Consultancy Limited | Other services | 2026 |
| Adpt Social Limited | Other services | 2025 |
| ADR100 Ltd | Professional & scientific | 2026 |
| Adrian Carpentry Limited | Construction | 2024 |
| Adrian Exec Ltd | Transport & logistics | 2026 |
| ADS Alliance Limited | Real estate | 2024 |
| ADS on Wheels Limited | Professional & scientific | 2025 |
| Adsidera Ltd | Professional & scientific | 2007 |
| Advance Autotech Limited | Wholesale & retail | 2010 |
| Advance on One Ltd. | Real estate | 1999 |
| Advanced Portable Roadway Ltd | Construction | 2005 |
| Advanced Scaffolding SOLUTIONS1 (UK) Limited | Construction | 2025 |
| Advertisi Ltd | Wholesale & retail | 2026 |
| Adwj Limited | Professional & scientific | 2025 |
| AE 2026 Limited | Professional & scientific | 2026 |
| AE Supreme Cleaning and Maintenance Ltd | Administrative & support | 2025 |
| Aedes Rediviva Ltd | Construction | 2025 |
| Aegidius Solutions Limited | Administrative & support | 2024 |
| Aegle Consultancy Ltd | Professional & scientific | 2023 |
| Aeglesburgh Watermead Limited | Hospitality | 2013 |
| AEI Enterprise Ltd | Hospitality | 2025 |
| Aeion Ltd | Construction | 2022 |
| Aept Ltd | Arts & recreation | 2022 |
| AER Solutions Services Ltd | Administrative & support | 2024 |
| Aerome Consultants Limited | Professional & scientific | 2020 |
| Aesthetic Derma Ltd | Other services | 2021 |
| Aestheticare by Raluca Ltd | Wholesale & retail | 2025 |
| Aesthetics Care Limited | Other services | 2024 |
| Aeviya Ltd | Wholesale & retail | 2025 |
| Aeykay Enterprises Ltd | Professional & scientific | 2025 |
| AF Plumbing and Heating Ltd | Construction | 2023 |
| AFC Enterprises Limited | Other services | 2020 |
| Affinity Hair Design Ltd | Other services | 2025 |
| Affinity Invest Ltd | Real estate | 2024 |
| Affinity New Homes Limited | Extraterritorial | 2009 |
| Affo Limited | Manufacturing | 2023 |
| Affordable Mobile Tyres Ltd | Wholesale & retail | 2025 |
| Afishal Music Ltd | Administrative & support | 2016 |