| ACN Property Services Ltd | Real estate | 2007 |
| ACO City Ware Limited | Wholesale & retail | 2025 |
| Acolasiai Ltd | Wholesale & retail | 2025 |
| Acom Dgtl Ltd | Information & communication | 2020 |
| Acomex Limited | Professional & scientific | 2017 |
| Acon College Ltd | Education | 2025 |
| Acordis UK Limited | Manufacturing | 1918 |
| Acorduk Limited | Construction | 2025 |
| Acorn Civil Engineering Ltd | Construction | 2020 |
| Acorn Construction (South Wales) Limited | Construction | 1983 |
| Acorn Homecover Limited | Construction | 2025 |
| Acorn Place Management Limited | Households | 2013 |
| Acorn Press Swindon Limited | Manufacturing | 1988 |
| Acorn Property Rentals UK Ltd | Households | 2022 |
| Acorn Riley Ltd | Education | 2025 |
| Acornface Limited | Real estate | 2023 |
| Acorns (Holdings) Limited | Administrative & support | 2018 |
| Acorns Nurseries Limited | Health & social care | 1995 |
| Acountn Services Limited | Professional & scientific | 2023 |
| Acoustic Ceilings Limited | Construction | 1995 |
| Acquda Solutions Limited | Administrative & support | 2021 |
| Acquire Sign Ltd. | Manufacturing | 2016 |
| Acquisition Systema Limited | Information & communication | 2025 |
| Acquisitionclients Ltd | Wholesale & retail | 2024 |
| Acquisitionify Ltd | Professional & scientific | 2016 |
| ACR Recruitment Solutions Ltd | Administrative & support | 2009 |
| Acre Retreats Ltd | Construction | 2025 |
| Acreetr Ltd | Real estate | 2021 |
| Acretone Limited | Health & social care | 2026 |
| Acrevale Digital Limited | Administrative & support | 2025 |
| Acrevale Group Limited | Financial services | 2025 |
| Acrevale Installations Limited | Construction | 2025 |
| Acrevale Property Solutions Limited | Real estate | 2025 |
| Acrm Property Ltd | Real estate | 2022 |
| Acro Yoga Travels Limited | Manufacturing | 2022 |
| Acronym Biosciences Ltd | Financial services | 2018 |
| Across Wales Travel Club Ltd | Transport & logistics | 2023 |
| Acrowtrans Ltd | Transport & logistics | 2018 |
| Acrylic Pictures Limited | Extraterritorial | 2010 |
| ACS Business Limited | Wholesale & retail | 2016 |
| ACS Physical Risk Control Limited | Professional & scientific | 2006 |
| ACS Ventures Ltd | Financial services | 2020 |
| Acsa Capital Ltd | Financial services | 2024 |
| ACT IT Limited | Education | 1987 |
| ACT Outdoors Limited | Extraterritorial | 2011 |
| Actennoveo International Group Ltd | Professional & scientific | 2023 |
| Actfast Consultancy Limited | Professional & scientific | 2019 |
| Actgold Int'L Trading Limited | Professional & scientific | 2008 |
| Action Airconditioning Limited | Energy | 1996 |
| Action for Children (Wales) Ltd | Health & social care | 2016 |
| Action for Elders Trust | Health & social care | 2011 |
| Action LET Ltd | Real estate | 2019 |
| Action Mart Ltd | Wholesale & retail | 2026 |
| Action Petz Franchise Ltd | Professional & scientific | 2015 |
| Action Plus Consulting Ltd | Administrative & support | 2019 |
| Action Rail & Civil Engineering Ltd | Professional & scientific | 2017 |
| Action Rail Civics Limited | Construction | 2017 |
| Actionfordogs Ltd | Transport & logistics | 2019 |
| Actionzone Limited | Hospitality | 2014 |
| Actisys Limited | Information & communication | 2019 |
| Activ Marketing Group Limited | Professional & scientific | 2020 |
| Activ PM Limited | Administrative & support | 2018 |
| Activ Product Services Ltd | Wholesale & retail | 2014 |
| Activa LLP | | 2025 |
| Activant Solution Ltd | Hospitality | 2019 |
| Activate FUN Ltd | Arts & recreation | 2017 |
| Activatehappy Ltd | Wholesale & retail | 2024 |
| Active Accounts Payroll Ltd | Professional & scientific | 2021 |
| Active Care Security Limited | Administrative & support | 2024 |
| Active Covers Ltd | Manufacturing | 2024 |
| Active Fit Ltd | Other services | 2018 |
| Active Gamers Ltd | Education | 2012 |
| Active Hire Solutions Ltd | Administrative & support | 2020 |
| Active Indoor Leisure Limited | Arts & recreation | 2018 |
| Active IO Limited | Wholesale & retail | 2017 |
| Active Learning & Development Limited | Professional & scientific | 1990 |
| Active Media Group Limited | Information & communication | 2021 |
| Active Perfusion Services Ltd | Health & social care | 2013 |
| Active Search Limited | Administrative & support | 2016 |
| Activefit Workforce Ltd | Education | 2018 |
| Activequote Limited | Information & communication | 2008 |
| ACTIVITIS4KIDS Limited | Health & social care | 2020 |
| Activity Ventures Ltd | Wholesale & retail | 2024 |
| Actoris Chippenham Limited | Construction | 2025 |
| Actoris Clubland Limited | Real estate | 2010 |
| Actoris Developments Limited | Real estate | 2008 |
| Actoris Property Limited | Construction | 2017 |
| Actorsworkshop LLP | | 2003 |
| Actotum Limited | Administrative & support | 2019 |
| Actual Staff Ltd | Administrative & support | 2024 |
| Actual Staffing Ltd | Administrative & support | 2022 |
| Actualisers Limited | | 1979 |
| Actuly Limited | Information & communication | 2024 |
| Acucy Homes Limited | Construction | 2019 |
| Acuitas Executive Search & Advisory Limited | Administrative & support | 2015 |
| Acuity DPO Limited | Professional & scientific | 2018 |
| Acuity Edtech (UK) Ltd | Education | 2022 |
| Acuity Law Group Limited | Professional & scientific | 2018 |
| Acuity Law Holdings Limited | Financial services | 2023 |
| Acuity Law Limited | Professional & scientific | 2011 |