| Alphapronic Solutions Limited | Wholesale & retail | 2017 |
| Alphazenith Limited | Information & communication | 2020 |
| Alpine Access Limited | Administrative & support | 2020 |
| Alpine Heating and Drying Limited | Administrative & support | 2020 |
| Alpine Hire Limited | Administrative & support | 2002 |
| Alpine Lifting Limited | Administrative & support | 2020 |
| Alpla Recycling UK Ltd | Professional & scientific | 2018 |
| Alpla UK Limited | Manufacturing | 1990 |
| Alpo Developments Ltd | Professional & scientific | 2021 |
| Alptest Ltd | Professional & scientific | 2020 |
| ALR Process Services Limited | Administrative & support | 2014 |
| ALS Plumbing Limited | Construction | 2017 |
| Also Media Ltd | Information & communication | 2000 |
| Alta Digital Ltd | Professional & scientific | 2007 |
| Altaris Group Limited | Financial services | 2026 |
| Altavista Software Solutions Limited | Information & communication | 2019 |
| Altcom 431 Limited | Extraterritorial | 2007 |
| Altenburg Advisory LLP | | 2020 |
| Alternative Aquatics Limited | Extraterritorial | 1998 |
| Altins Catering Ltd | Hospitality | 2019 |
| Altitude Scaffolding Limited | Professional & scientific | 1971 |
| Altostratus Nine Limited | Information & communication | 2015 |
| Altrad Babcock Energy Services (Overseas) Limited | Manufacturing | 1968 |
| Altrad Babcock Limited | Manufacturing | 1965 |
| Altrad Babcock Power Systems Overseas Investments Limited | Manufacturing | 1996 |
| Altrad Employment Services Limited | Administrative & support | 2018 |
| Altrad Energy Support Services Limited | Administrative & support | 2003 |
| Altrad Engineering Services Limited | Manufacturing | 1994 |
| Altrad Environmental Services Offshore Limited | Administrative & support | 1999 |
| Altrad Environmental Services Onshore Limited | Administrative & support | 1996 |
| Altrad Motherwell Bridge Limited | Construction | 2008 |
| Altrad NSG Limited | Manufacturing | 2010 |
| Altrad Services Limited | Construction | 1997 |
| Altrad Support Services Limited | Construction | 1975 |
| Altrad UK Limited | Professional & scientific | 2017 |
| Altrad York Linings Limited | Construction | 1974 |
| Altrincham Town Centre Plan Limited | Professional & scientific | 2014 |
| Altrscents Limited | Wholesale & retail | 2025 |
| Altrum UK Limited | Professional & scientific | 2013 |
| Alturas Consulting Services Limited | Administrative & support | 2012 |
| Altwood Business Development Limited | Administrative & support | 2013 |
| Alvanley Farms Limited | Agriculture & fishing | 1992 |
| Alveca Building Consultancy Limited | Administrative & support | 2010 |
| Alward Ltd | Health & social care | 2022 |
| Always There Care Ltd | Health & social care | 2025 |
| Alweld Limited | Wholesale & retail | 2006 |
| AM Air Limited | Manufacturing | 2026 |
| AM Aspirations Limited | Administrative & support | 2015 |
| AM Business Solutions Limited | Professional & scientific | 2007 |
| AM Kennedy Consulting Limited | Information & communication | 2023 |
| AM Offshore Ltd | Information & communication | 2026 |
| AM PM Digital Limited | Administrative & support | 2015 |
| AM Rathor Limited | Public administration | 2018 |
| AM Supplies Limited | Wholesale & retail | 2011 |
| AM Taxi Express Ltd | Transport & logistics | 2025 |
| AM Tennis Ltd | Arts & recreation | 2019 |
| Amag Transport Ltd | Transport & logistics | 2021 |
| Amalgamate Group Ltd | Professional & scientific | 2024 |
| Amalgamate Limited | Administrative & support | 2015 |
| Amalia AMY Ltd | Transport & logistics | 2018 |
| Amanda Birnie Ltd | Other services | 2022 |
| Amanda Leathem Design Limited | Construction | 2011 |
| Amanda WAH Fitness CIC | Education | 2025 |
| Amani Care Resolutions Ltd | Health & social care | 2025 |
| Amani Engineering Limited | Administrative & support | 2011 |
| AMANICARE15 Ltd | Health & social care | 2019 |
| Amantius Limited | Professional & scientific | 2006 |
| Amazing Drivers Limited | Transport & logistics | 2020 |
| Amba Outsourcing Services Limited | Administrative & support | 2021 |
| Ambe Fire Ltd | Professional & scientific | 2020 |
| Amber Rose Homes Limited | Financial services | 2020 |
| Amberglow Fireplaces Limited | Wholesale & retail | 2003 |
| Amberway Management Services Limited | Administrative & support | 2026 |
| Amberwood UK Property Ltd | Real estate | 2023 |
| AMC (NW) Limited | Manufacturing | 2008 |
| AMC Vitality Limited | Arts & recreation | 2024 |
| AMC06 Limited | Administrative & support | 2015 |
| Amcc Engineering Limited | Professional & scientific | 2022 |
| Amcd Events Limited | Other services | 2019 |
| AMD Products Ltd | Manufacturing | 2010 |
| Amentum (UK) Ltd. | Water & waste | 2000 |
| Amentum Clean Energy International Limited | Professional & scientific | 1996 |
| Amentum Clean Energy Limited | Construction | 1973 |
| Amentum E&C Limited | Construction | 2003 |
| Amentum Enterprise Asset Solutions Construction Limited | Construction | 2013 |
| Amentum Enterprise Asset Solutions Limited | Manufacturing | 1974 |
| Amentum Facility Management UK Ltd. | Administrative & support | 2002 |
| Amentum International Holdings UK Ltd. | Professional & scientific | 1954 |
| Amentum International Nuclear Services Limited | Professional & scientific | 2005 |
| American Golf (Leisure) Limited | Arts & recreation | 2021 |
| American Golf (Trading) Limited | Wholesale & retail | 2018 |
| American Sweets Empire Ltd | Wholesale & retail | 2022 |
| Americanu Construction Ltd | Construction | 2019 |
| Ameritz Music Limited | Arts & recreation | 2007 |
| Ameritz Properties Limited | Financial services | 2026 |
| Amerwoods Limited | Information & communication | 2010 |
| Amerwoods Properties Limited | Real estate | 2018 |
| Ameryst Services Limited | Professional & scientific | 2021 |
| Amethyst Capital Holdings Limited | Financial services | 2023 |
| Amethyst Leadership Limited | Professional & scientific | 2022 |