| Aroquad Ltd | Information & communication | 2016 |
| Arora Design Limited | Administrative & support | 2001 |
| Around the Clock Healthcare Ltd | Health & social care | 2018 |
| ARP Global Ltd | Information & communication | 2013 |
| Arrakis Property Investments Limited | Real estate | 2024 |
| Arrek Limited | Real estate | 2021 |
| Arrow Autos Ltd | Wholesale & retail | 2026 |
| Arrowville Artworks Ltd | Arts & recreation | 2021 |
| ARS Soft Ltd | Information & communication | 2013 |
| Arshoo Limited | Wholesale & retail | 2023 |
| Art & Festa London Ltd | Hospitality | 2015 |
| Art and Experience Design Ltd | Information & communication | 2021 |
| Art Engine Limited | Professional & scientific | 2023 |
| Art OR NOT Ltd | Manufacturing | 2025 |
| Art Parquet Ltd | Construction | 2011 |
| Arta Private Limited | Real estate | 2024 |
| Artak Consultancy Ltd | Financial services | 2025 |
| Artbanner Ltd | Real estate | 2001 |
| Artee Designs Ltd | Wholesale & retail | 2013 |
| Artee.Ee Ltd | Manufacturing | 2024 |
| Artego Limited | Professional & scientific | 2021 |
| Artemis House Management Limited | Households | 2017 |
| Arteze Limited | Information & communication | 2022 |
| Artfully Yours Creative Studio Ltd | Arts & recreation | 2025 |
| Arth Limited | Professional & scientific | 2022 |
| Arthur Ellis MHS C.I.C. | Education | 2019 |
| Artifex Group Ltd | Financial services | 2025 |
| Artifex Homes Limited | Construction | 2017 |
| Artifex Homes Property Ltd | Real estate | 2025 |
| Artificial Intelligence Digital Solutions Limited | Information & communication | 2024 |
| Artip Ltd | Construction | 2025 |
| Artisan Rollers Limited | Other services | 1988 |
| Artistrynest Ltd | Wholesale & retail | 2025 |
| Artizan Hair M.K. Limited | Other services | 2003 |
| Artko Trans Limited | Transport & logistics | 2019 |
| Artlc Ltd | Other services | 2022 |
| Artlook Software Limited | Other services | 2002 |
| Artokay Ltd | Wholesale & retail | 2011 |
| Arts Gateway MK Limited | Arts & recreation | 2008 |
| Arts Investments Ltd | Real estate | 2024 |
| Arts Stage Collective LLP | | 2026 |
| ARTS1 Limited | Education | 2009 |
| Artsthetic Limited | Arts & recreation | 2025 |
| Artsy Service Limited | Wholesale & retail | 2026 |
| Artworks Illustration Limited | Administrative & support | 2006 |
| Arudra Ltd | Real estate | 2025 |
| Arun Mistry Taxation Services Ltd | Professional & scientific | 2014 |
| Arun Rockall Holdings Limited | Financial services | 2017 |
| Arvensis Energy and Engineering Limited | Professional & scientific | 2017 |
| Arvman Investments Limited | Real estate | 2017 |
| Aryan MK Limited | Hospitality | 2024 |
| Arzesh Ltd | Information & communication | 2013 |
| AS Builders & Property Maintenance Ltd | Construction | 2026 |
| AS Conferences Ltd | Administrative & support | 2004 |
| AS EDS Consulting Ltd | Professional & scientific | 2024 |
| AS Safety Services Limited | Professional & scientific | 2025 |
| AS Verdi Ltd | Arts & recreation | 2012 |
| As&Aa Ltd | Wholesale & retail | 2022 |
| ASA IT Consultancy Limited | Information & communication | 2018 |
| ASA Medical Solutions Limited | Health & social care | 2014 |
| ASA Techservices Ltd | Information & communication | 2012 |
| Asaap Technologies Limited | Information & communication | 2025 |
| Asabsa Consultancy Ltd | Professional & scientific | 2020 |
| Asado MK Ltd | Hospitality | 2026 |
| Asantevoyage Limited | Administrative & support | 2015 |
| Asap International Transport Ltd | Transport & logistics | 2020 |
| Asass Limited | Health & social care | 2023 |
| ASB Events Ltd | Other services | 2024 |
| ASB Property Consultants Limited | Real estate | 2011 |
| ASB Tech Ltd | Information & communication | 2019 |
| ASC EOT Limited | Financial services | 2021 |
| ASC Financial Solutions Limited | Financial services | 2008 |
| ASC Wills and Estate Planning Limited | Professional & scientific | 2023 |
| Ascend Property Services Limited | Households | 2023 |
| Ascenity (UK) Ltd | Information & communication | 2024 |
| Ascent Immigration Services Ltd | Professional & scientific | 2008 |
| Ascent International Group Limited | Financial services | 2022 |
| Ascent PCN Ltd | Health & social care | 2022 |
| Ascent Property Ventures Limited | Real estate | 2022 |
| Ascerton House Limited | Financial services | 2018 |
| Ascot Healthcare Services (MK) Ltd | Health & social care | 2023 |
| Ascot United Football Club Limited | Arts & recreation | 2009 |
| Ascott Safety Services Limited | Administrative & support | 2018 |
| Asdeal Limited | Agriculture & fishing | 2019 |
| ASE Accounts Ltd | Professional & scientific | 2006 |
| ASE Estates Limited | Real estate | 2024 |
| Ase-Minu Ltd | Transport & logistics | 2020 |
| Aseda Care Ltd | Health & social care | 2018 |
| Asendi Limited | Professional & scientific | 2024 |
| ASF Said Ltd | Transport & logistics | 2015 |
| ASG Car Cleaning Ltd | Other services | 2018 |
| ASG Click Ltd | Wholesale & retail | 2025 |
| ASG Epos Solutions Limited | Administrative & support | 2008 |
| ASG MK Foods Ltd | Hospitality | 2019 |
| Asgaard Solutions Limited | Professional & scientific | 2020 |
| ASH Engineering (U.K.) Limited | Manufacturing | 2003 |
| ASH K Homes Ltd | Health & social care | 2017 |
| ASH Properties Group Ltd | Real estate | 2022 |
| ASH Solar Renewables Ltd | Construction | 2021 |
| ASH White Limited | Real estate | 1986 |