| Activia Solar Ltd | Construction | 2012 |
| Activit Consulting Ltd | Information & communication | 2018 |
| Acton Coachworks Sports & Prestige Ltd | Wholesale & retail | 2020 |
| Acton Engineering and Management Ltd | Real estate | 2018 |
| Actualfact Limited | Real estate | 1999 |
| Actualise Business Consultancy Ltd | Administrative & support | 2013 |
| Actuary MAN Ltd | Financial services | 2023 |
| Acuk Management Ltd | Financial services | 2022 |
| ACW Moor Park Ltd | Wholesale & retail | 2025 |
| ACW Software Services Limited | Information & communication | 2012 |
| AD Alta Advisory Limited | Professional & scientific | 2016 |
| AD Infinitum Consultants Ltd | Professional & scientific | 2023 |
| AD Legal Services Limited | Real estate | 2016 |
| AD Success Limited | Professional & scientific | 2023 |
| Ad/Cd Ltd | Administrative & support | 2019 |
| ADA Consultancy Limited | Administrative & support | 2015 |
| ADA Rocket Ltd | Information & communication | 2018 |
| Adalina Limited | Information & communication | 2024 |
| Adam's Refurbishment Service Ltd | Construction | 2016 |
| Adamantis.J.A Limited | Health & social care | 2013 |
| Adamas Accountancy and Business Services Limited | Professional & scientific | 2025 |
| Adamico Limited | Real estate | 2019 |
| Adamis Capital Ltd | Financial services | 2024 |
| Adams Concept Ltd | Administrative & support | 2015 |
| Adams Group Real Estate Ltd | Professional & scientific | 2014 |
| Adams Testing Limited | Information & communication | 2002 |
| Adapt Childcare Solutions Ltd | Administrative & support | 2022 |
| ADAPTED4 Limited | Construction | 2018 |
| Adaptwell Limited | Professional & scientific | 1988 |
| Adara Consultancy Limited | Real estate | 2015 |
| Adas Centres Limited | Wholesale & retail | 2019 |
| Aday Landscaping Ltd | Professional & scientific | 2025 |
| ADD 4 U Ltd | Professional & scientific | 2020 |
| ADD on Ltd | Wholesale & retail | 2024 |
| Adda Hotels | Hospitality | 1966 |
| Addai Business and Technology Consulting Limited | Information & communication | 2015 |
| Added Value Ventures Limited | Professional & scientific | 2021 |
| Additive Instruments Limited | Professional & scientific | 2019 |
| Addventure Tours Limited | Administrative & support | 2018 |
| ADE Electrical Limited | Construction | 2026 |
| Adebiyi Ventures Ltd | Wholesale & retail | 2024 |
| Adeleke Adefarasin Ltd | Wholesale & retail | 2004 |
| Adelidi Limited | Wholesale & retail | 2023 |
| Aderni Ltd | Real estate | 2011 |
| Adeshi Ground Limited | Administrative & support | 2026 |
| ADI & Co Payroll Services Ltd | Professional & scientific | 2020 |
| ADI 99 Investment Limited | Transport & logistics | 2015 |
| ADI Installation Ltd | Construction | 2019 |
| Adira Solutions Ltd | Information & communication | 2020 |
| Adit Ltd | Information & communication | 2022 |
| Aditri IT Solutions Ltd | Information & communication | 2010 |
| Aditri Properties Ltd | Real estate | 2026 |
| Adits Gruham Ltd | Real estate | 2023 |
| Adjust Software Limited | Professional & scientific | 2012 |
| ADL Management Solutions Ltd | Professional & scientific | 2026 |
| Admire HR Services Ltd | Administrative & support | 2018 |
| Admixer Limited | Professional & scientific | 2014 |
| Adnic International Ltd | Financial services | 2017 |
| ADO Building Company Limited | Construction | 2006 |
| ADO Properties Ltd | Real estate | 2017 |
| Adom Organisation Ltd | Public administration | 2025 |
| Adomicile Care Services Limited | Health & social care | 2019 |
| Adon Prestige UK Ltd | Wholesale & retail | 2019 |
| Adorn Aesthetic London Ltd | Other services | 2021 |
| Adorn Beauty Limited | Other services | 2008 |
| Adorn Properties Ltd | Real estate | 2017 |
| Adorn Properties One Ltd | Real estate | 2019 |
| Adorn Spa Limited | Other services | 2010 |
| Adrian Plumbing and Building Ltd | Construction | 2019 |
| Adry & ANA Cleaning Ltd | Administrative & support | 2023 |
| ADS Independent Living Solutions Limited | Administrative & support | 2015 |
| Adseenit Ltd | Information & communication | 2018 |
| Adsencov Ltd | Hospitality | 2021 |
| Adskel Limited | Professional & scientific | 2022 |
| Adsp Property Limited | Real estate | 2024 |
| Adtlas Marketing Limited | Professional & scientific | 2024 |
| Advance International Ltd | Wholesale & retail | 2023 |
| Advanced Development and Financial Company Limited | Professional & scientific | 2009 |
| Advanced Heating & Plumbing Limited | Construction | 1999 |
| Advanced Racking Solutions Limited | Construction | 2018 |
| Advanced Sedani Limited | Health & social care | 2022 |
| Advanced Technology Manufacture Ltd | Wholesale & retail | 2020 |
| Advanced Test Ltd | Professional & scientific | 2012 |
| Advantage Employment and Training Solutions Ltd | Administrative & support | 1997 |
| Advantage Herts Ltd | Real estate | 2018 |
| Adven Ltd | Wholesale & retail | 2021 |
| Advent Advisors Limited | Administrative & support | 2010 |
| Advent Global Ltd | Professional & scientific | 2023 |
| Adventist Radio London | Information & communication | 2017 |
| Adventure Estates Ltd | Construction | 2017 |
| Adventure Power Limited | Construction | 2019 |
| Adverbuzz Ltd | Information & communication | 2025 |
| Advi Technologies Limited | Information & communication | 2013 |
| Advice Points Ltd | Professional & scientific | 2016 |
| Advr Associates Ltd | Information & communication | 2024 |
| Advyan Limited | Professional & scientific | 2024 |
| Adwaviation Ltd | Professional & scientific | 2024 |
| Aegis Oral Health Ltd | Health & social care | 2024 |
| AEM Development Group Ltd | Information & communication | 2026 |
| AEM UK Group Ltd | Wholesale & retail | 2023 |