| Aligned Limited | Extraterritorial | 2009 |
| Alignment Systems Ltd | Construction | 2002 |
| Alinco Properties Ltd | Real estate | 2013 |
| Alinco Services Limited | Professional & scientific | 2012 |
| Alinggi Management Limited | Real estate | 2026 |
| Alison Learner Mortgages Limited | Financial services | 2023 |
| Aliwhite Limited | Real estate | 2009 |
| Alkasbahh Ltd | Hospitality | 2024 |
| Alkemist Limited | Professional & scientific | 2015 |
| ALL in One Marketing Limited | Administrative & support | 2011 |
| ALL Metal Recycling Ltd | Water & waste | 2010 |
| ALL Seasons Accommodation Ltd | Hospitality | 2010 |
| ALL Stars Chicken Ltd | Hospitality | 2024 |
| ALL Things Catered Limited | Hospitality | 2009 |
| Allana Melody Charles Ltd | Extraterritorial | 2024 |
| Allasso Recycling Limited | Construction | 2013 |
| Allen & York (Built and Natural Environment) Ltd. | Administrative & support | 1999 |
| Allen Builders Limited | Construction | 2019 |
| Allen Developments Limited | Construction | 1984 |
| Alley Cats of London Limited | Administrative & support | 2007 |
| Allsaints Studio (ST Albans) Limited | Arts & recreation | 2017 |
| Almos International Limited | Professional & scientific | 2016 |
| Alpe Capital Holdings Limited | Financial services | 2018 |
| Alpe Capital Limited | Financial services | 2020 |
| Alpha Energy Assessors Ltd | Professional & scientific | 2009 |
| Alpha Omega London Construction Services Ltd | Construction | 2024 |
| Alpha Plumbers Ltd | Construction | 2024 |
| Alpha Pneumatic Supplies Limited | Wholesale & retail | 1994 |
| Alphaora Ltd | Professional & scientific | 2025 |
| Alroy Carpets Limited | Wholesale & retail | 2002 |
| Alternative Barbering Berkhamsted Limited | Other services | 2017 |
| Alternative Barbering Company Hitchin Limited | Other services | 2019 |
| Alternative Barbering Limited | Other services | 2012 |
| Alternative Sentiments Ltd | Wholesale & retail | 2021 |
| Altitude Financial Limited | Professional & scientific | 2017 |
| Altla Ltd | Professional & scientific | 2025 |
| Altor Support Limited | Administrative & support | 2010 |
| Altra Energy Holding Limited | Financial services | 2020 |
| Altra Energy Limited | Professional & scientific | 2020 |
| Alturos Technologies Ltd | Information & communication | 2025 |
| Alvin Woolley Associates Ltd | Administrative & support | 2012 |
| Always Building Limited | Construction | 2011 |
| AM Reinforcement Ltd | Construction | 2015 |
| AMA Shah Properties Ltd | Real estate | 2026 |
| Amalily Ltd | Wholesale & retail | 2020 |
| Amana Residence Limited | Real estate | 2025 |
| Amanda Huberman Ltd | Hospitality | 2016 |
| Amanuel Electrical Ltd | Construction | 2025 |
| Amaris Advisory & Consulting Limited | Financial services | 2022 |
| Amastan Limited | Administrative & support | 2022 |
| Amau Ltd | Information & communication | 2021 |
| Amayah Ltd | Wholesale & retail | 2024 |
| Amazeway International Limited | Transport & logistics | 2025 |
| Amber House Construction Limited | Construction | 2017 |
| Amber Property Development Group Limited | Real estate | 2020 |
| Amber Real Investment Limited | Construction | 2018 |
| Amberósia Ltd | Education | 2026 |
| Ambs Eco Limited | Construction | 2021 |
| Ambs Eco Solutions Limited | Construction | 2020 |
| Amcam London Ltd | Professional & scientific | 2025 |
| Amch Properties Limited | Real estate | 2021 |
| Ame-Creative Limited | Administrative & support | 2010 |
| Amelo Holdings Limited | Financial services | 2023 |
| American Drinks Limited | Wholesale & retail | 2004 |
| Amgcleaning Ltd | Administrative & support | 2014 |
| AMI Associates Limited | Professional & scientific | 1999 |
| AMI Squared Ltd | Information & communication | 2021 |
| Amity Group Limited | Professional & scientific | 1991 |
| AMJ Properties and Management Ltd | Households | 2025 |
| AML Motors Ltd | Wholesale & retail | 2024 |
| Amlay Advisory Limited | Professional & scientific | 2023 |
| Amlgt Ltd | Arts & recreation | 2025 |
| Amonty Ltd | Wholesale & retail | 2022 |
| Amora Coffee Ltd | Hospitality | 2025 |
| Amorra Ltd | Manufacturing | 2025 |
| Amos Construct Ltd | Construction | 2023 |
| Amoura Labs Ltd | Wholesale & retail | 2026 |
| Amped AV Ltd | Professional & scientific | 2019 |
| Amthal Group Holdings Limited | Other services | 2021 |
| Amthal Investments (Midlands) Limited | Real estate | 2023 |
| AMY Gardiner Accountancy Limited | Professional & scientific | 2019 |
| AMZ Coaching Ltd | Professional & scientific | 2020 |
| AN Englishman's Castle Limited | Financial services | 2016 |
| AN Lettings Ltd | Real estate | 2024 |
| AN Technosis Limited | Information & communication | 2015 |
| ANA Martin Limited | Administrative & support | 2016 |
| Anakar Holdings Limited | Financial services | 2020 |
| Anakar Lettings Limited | Real estate | 2020 |
| Anakar Properties Limited | Real estate | 2020 |
| Anam Cara Equine Ltd | Health & social care | 2019 |
| Anaporate Ltd | Professional & scientific | 2013 |
| Anaserv Creative Limited | Wholesale & retail | 2009 |
| Anaserv Limited | Administrative & support | 2006 |
| ANB Technology Ltd | Information & communication | 2017 |
| ANC Advisory Ltd | Professional & scientific | 2022 |
| Anca Bratu Limited | Health & social care | 2019 |
| Ancoba Ltd | Construction | 2021 |
| Anderson Moss Ltd | Professional & scientific | 2023 |
| Andi AI Ltd | Information & communication | 2026 |
| Andover Care Ltd | Health & social care | 2017 |