| AP9 Ltd | Real estate | 2025 |
| Apex Aerospace Ltd | Information & communication | 2025 |
| Apex Home Cleaning Limited | Administrative & support | 2025 |
| Apex Innovations London Limited | Information & communication | 2023 |
| APK Construction Ltd. | Construction | 2017 |
| APK Developers Ltd | Real estate | 2018 |
| APK Installations Limited | Construction | 2014 |
| APK Property Management Ltd | Households | 2019 |
| APK Yard Limited | Wholesale & retail | 2020 |
| Apkharmonyhomes Ltd | Construction | 2025 |
| Apollo Commercials Limited | Real estate | 2011 |
| Apollo Dance Limited | Arts & recreation | 2021 |
| Apollo Fundraising Limited | Professional & scientific | 2016 |
| Appcalibre Limited | Information & communication | 2017 |
| Appone Microservices UK Limited | Information & communication | 2019 |
| Appwest Limited | Information & communication | 2020 |
| APT Developers Limited | Construction | 2017 |
| APT Recycling Limited | Water & waste | 2016 |
| APT Scaffolding Ltd | Construction | 2008 |
| APT Structures Limited | Construction | 2011 |
| Aptus Global Limited | Professional & scientific | 2018 |
| AQD Online Ltd | Other services | 2020 |
| Aquamarine (Holdings) Limited | Administrative & support | 2006 |
| Aquamarine(London)Limited | Administrative & support | 1985 |
| Aquisitions Investment Group Ltd | Professional & scientific | 2015 |
| AR Building Management Limited | Professional & scientific | 2016 |
| AR9 Ventures Limited | Wholesale & retail | 2025 |
| Arabic Language Academy Ltd | Education | 2024 |
| Arcadia Peak LLP | | 2025 |
| Arche DE L'Alliance Limited | Other services | 2019 |
| Archiality Ltd | Professional & scientific | 2010 |
| Archimedes Property Ltd | Real estate | 2023 |
| Ardent Tech Ltd | Education | 2021 |
| ARF Technologies Ltd | Professional & scientific | 2024 |
| Arhz IT Services Limited | Information & communication | 2016 |
| Aries Energy Solutions Ltd | Manufacturing | 2024 |
| ARK Nest Ltd | Real estate | 2019 |
| Arkanetri Limited | Real estate | 2026 |
| Arkr Limited | Health & social care | 2014 |
| Arkwright London Ltd | Professional & scientific | 2020 |
| Arleta on Track Ltd | Administrative & support | 2022 |
| Armenian Church Trust (UK) Limited | Other services | 2010 |
| Armored Auto (UK) LP | | 2010 |
| Armstrong Cuthbert Hairdressing Limited | Other services | 2007 |
| Arnold Property Solutions Ltd | Extraterritorial | 2012 |
| Aromgain Limited | Professional & scientific | 1998 |
| Arquen Consulting Limited | Professional & scientific | 2020 |
| Arranmore Properties Limited | Real estate | 2016 |
| Artful Dodger London Limited | Arts & recreation | 2016 |
| Arthur Jack Limited | Construction | 2019 |
| AS4EV Ltd | Wholesale & retail | 2022 |
| Asalih Restoration Ltd | Construction | 2021 |
| Ascend Vintage Limited | Wholesale & retail | 2020 |
| Ascension Films Limited | Professional & scientific | 2007 |
| Ascent Crystal Limited | Wholesale & retail | 2021 |
| Ascent One Ltd | Information & communication | 2025 |
| Asco Cars Ltd | Wholesale & retail | 2020 |
| Asel Zehra Limited | Hospitality | 2025 |
| ASH Parsa Limited | Information & communication | 2016 |
| Ashbo Ltd | Administrative & support | 2014 |
| Ashtekone Limited | Information & communication | 2022 |
| ASK Solutions London Limited | Information & communication | 2023 |
| ASK Structural Ltd | Professional & scientific | 2012 |
| Askeco Ltd | Education | 2024 |
| ASM Supermarket Ltd | Wholesale & retail | 2015 |
| Asna UK Ltd | Transport & logistics | 2008 |
| Aspinal Security Limited | Administrative & support | 2022 |
| Aspire Information Technologies Limited | Information & communication | 2012 |
| ASR Bought for Letting Limited | Real estate | 2020 |
| ASR Buy to LET Limited | Real estate | 2018 |
| ASR Buying and Letting Limited | Real estate | 2019 |
| Asset Check Limited | Professional & scientific | 2016 |
| Association of Indoor Play Ltd | Other services | 2020 |
| Asta Movers Limited | Transport & logistics | 2017 |
| Aston Gowman Limited | Professional & scientific | 2017 |
| Astoria Homecare Limited | Health & social care | 2016 |
| Asurion Soluto Europe Limited | Information & communication | 2016 |
| Atelier Noon Ltd | Professional & scientific | 2022 |
| Atelier V Ltd | Professional & scientific | 2018 |
| Athos Chauffeurs Ltd | Transport & logistics | 2017 |
| Atlas Infusion Ltd | Health & social care | 2023 |
| Atlas Unitrade Ltd | Wholesale & retail | 2024 |
| Atom Records Limited | Information & communication | 2022 |
| Atomic Floyd Limited | Administrative & support | 2013 |
| Atomic Services Limited | Administrative & support | 2012 |
| Attend IT Limited | Transport & logistics | 2007 |
| Attok Care Services Ltd | Health & social care | 2012 |
| Atya Limited | Financial services | 2022 |
| Audience XL Limited | Professional & scientific | 2022 |
| Augustus 1 Limited | Financial services | 2004 |
| Augustus 2 Limited | Financial services | 2004 |
| Auhha Ltd | Financial services | 2024 |
| AUR Project Management and Consulting Limited | Professional & scientific | 2011 |
| Aura Homecare Group Ltd | Health & social care | 2025 |
| AURA9 Limited | Wholesale & retail | 2013 |
| Ausmek Construction Ltd | Construction | 2018 |
| Aussie Holdings Limited | Financial services | 2025 |
| Aussie KEW Bridge 11 Limited | Wholesale & retail | 2025 |
| Auto Car Parts UK Ltd | Manufacturing | 2023 |
| Auto Motors TSH Ltd | Wholesale & retail | 2020 |