| ACT Property Limited | Real estate | 2016 |
| Acta 201 Ltd | Information & communication | 2015 |
| Actandrest Limited | Wholesale & retail | 2019 |
| Actif Estates Ltd. | Real estate | 2002 |
| Actif Management Limited | Real estate | 1996 |
| Action 365 Ltd | Information & communication | 1999 |
| Action Station North West Community Interest Company | Wholesale & retail | 2021 |
| ACTION18 Healthcare Ltd | Health & social care | 2018 |
| Actionearly Limited | | 1986 |
| Actionmood Limited | | 1986 |
| Actionnaire Consulting Limited | Professional & scientific | 2019 |
| Actionquarter Limited | Construction | 1997 |
| Actiphons Limited | Information & communication | 2016 |
| Activ Group Ltd | Administrative & support | 2021 |
| Activ Project Management Limited | Other services | 2016 |
| ACTIV8 Services Ltd | Professional & scientific | 2019 |
| Activate Education Limited | Education | 2017 |
| Activation International (UK) Limited | Professional & scientific | 2022 |
| Activcorp Limited | Information & communication | 2010 |
| Active 360 Ltd | Wholesale & retail | 2021 |
| Active Aluminium Systems Ltd | Manufacturing | 2011 |
| Active and Shine Cleaning Ltd | Administrative & support | 2025 |
| Active Care Injury Ltd | Health & social care | 2020 |
| Active Care Pro Rehab Ltd. | Health & social care | 2015 |
| Active Certification Services Register Ltd | Professional & scientific | 2021 |
| Active Choice Solutions Ltd | Other services | 2021 |
| Active CLU8 Limited | Wholesale & retail | 2024 |
| Active Constructions Ltd | Other services | 2013 |
| Active Contract Management Limited | Administrative & support | 2021 |
| Active Cosmetics Limited | Professional & scientific | 2001 |
| Active Fleet Management Limited | Financial services | 2018 |
| Active Games Limited | Information & communication | 2025 |
| Active Kidney Innovation Ltd | Health & social care | 2019 |
| Active Life Therapy Ltd | Other services | 2018 |
| Active PAY Ltd | Financial services | 2026 |
| Active Plus Accounting Limited | Professional & scientific | 2025 |
| Active Profile Limited | Professional & scientific | 2004 |
| Active Pulse EMS Ltd | Arts & recreation | 2025 |
| Active Scaleup Limited | Professional & scientific | 2023 |
| Active Services Group Ltd | Real estate | 2022 |
| Active Source Ltd | Wholesale & retail | 2026 |
| Active Talent Recruitment Ltd | Administrative & support | 2023 |
| Active Taxi Hire Limited | Professional & scientific | 2016 |
| Active Utilities Limited | Professional & scientific | 2014 |
| Activemark Ltd | Wholesale & retail | 2020 |
| Activemark Properties Ltd | Real estate | 2023 |
| Activestream Limited | Professional & scientific | 1992 |
| Activetrend Limited | Other services | 1989 |
| Activinvestors LP | | 2022 |
| Activist Talent Ltd | Administrative & support | 2020 |
| Activpayroll Group Limited | Financial services | 2019 |
| Acton Group NW Limited | Construction | 2015 |
| Acton Hall Farm LLP | | 2008 |
| Acton Private Capital Ltd | Financial services | 2026 |
| Actonview Ltd | Real estate | 2019 |
| Actorcard.Com Limited | Administrative & support | 2015 |
| Actron Global Limited | Wholesale & retail | 2025 |
| Actros for Trading Ltd | Wholesale & retail | 2025 |
| Actsharp Consulting Ltd | Information & communication | 2025 |
| Actual Housing Limited | Real estate | 2023 |
| Actuarial Risk Management UK Limited | Financial services | 2024 |
| Acucare for Life Limited | Health & social care | 2023 |
| Acuhold Limited | Financial services | 2013 |
| Acuitech Solutions Ltd | Information & communication | 2018 |
| Acuity Technologies Ltd | Information & communication | 2025 |
| Acumen Automation Ltd | Professional & scientific | 2026 |
| Acumen Fieldwork Limited | Professional & scientific | 2005 |
| Acumen Models Limited | Administrative & support | 2012 |
| Acumen Seals & Pumps Ltd | Wholesale & retail | 2012 |
| Acumension Limited | Administrative & support | 1998 |
| Acuna UK Ltd | Wholesale & retail | 2021 |
| Acurestore Health Clinic Ltd | Health & social care | 2025 |
| Acuri Ltd | Professional & scientific | 2025 |
| Acuscaff Limited | Construction | 2012 |
| Acuspa Ltd | Health & social care | 2013 |
| Acute Medical & Cardiovascular Limited | Health & social care | 2013 |
| ACY Cosmetics Holding Limited | Extraterritorial | 2020 |
| AD & BU Development Ltd | Construction | 2021 |
| AD 120 Ltd | Health & social care | 2025 |
| AD Accommodation Ltd | Real estate | 2024 |
| AD Alpha Solutions Ltd | Other services | 2016 |
| AD Astra Advertising Ltd | Professional & scientific | 2023 |
| AD Astra BC Ltd | Hospitality | 2021 |
| AD Astra Management Group Ltd | Financial services | 2022 |
| AD AUT0GLAZE Ltd | Wholesale & retail | 2025 |
| AD Bioenergy Cornwall Limited | Energy | 2015 |
| AD Bioenergy Holdings Limited | Energy | 2015 |
| AD Business Services Limited | Administrative & support | 2024 |
| AD Clothing Limited | Wholesale & retail | 2026 |
| AD Corporate Partnership Ltd | Professional & scientific | 2024 |
| AD Dynamo Holdings Limited | Information & communication | 2013 |
| AD Dynamo UK Limited | Information & communication | 2013 |
| AD Empire Interiors and Construction Ltd | Construction | 2019 |
| AD Florem Limited | Administrative & support | 2015 |
| AD Furniture Ltd | Wholesale & retail | 2025 |
| AD Global Partnership Ltd | Professional & scientific | 2025 |
| AD Group Global Limited | Administrative & support | 2024 |
| AD LIB TV Limited | Administrative & support | 2006 |
| AD Maiora ITA Ltd | Hospitality | 2023 |
| AD Medical Holdings Ltd | Financial services | 2025 |