| Maison Soléor Ltd | Wholesale & retail | 2026 |
| Maluk & JC Limited | Real estate | 2022 |
| Mama Love Kitchen Ltd | Hospitality | 2020 |
| Mampu Consulting Services Limited | Professional & scientific | 2016 |
| MAN Built Ltd | Construction | 2025 |
| MAN UP Energy Limited | Manufacturing | 2012 |
| Management Hub AI Limited | Information & communication | 2025 |
| Mandeep Ltd | Real estate | 2024 |
| MANDMSERVICES2 Ltd | Construction | 2020 |
| Mani Drylining Ltd | Construction | 2018 |
| MAP Wholesale Ltd | Wholesale & retail | 2020 |
| Marbin Estates Ltd | Real estate | 2021 |
| Maria Satchi Ltd | Health & social care | 2024 |
| Mariana Consulting Ltd | Professional & scientific | 2026 |
| Marie Property Limited | Real estate | 2023 |
| Marine Support Thames (MST) Limited | Transport & logistics | 2009 |
| Mario & Dany Limited | Construction | 2006 |
| Mark Wendleken Limited | Construction | 2015 |
| Martin Dene Sports Limited | Arts & recreation | 1935 |
| Martin J. Dewar Limited | Financial services | 2022 |
| Martin Langley Developments Limited | Real estate | 2014 |
| Martin Morrison & Co. Limited | Professional & scientific | 2006 |
| Marvel Freight UK Ltd | Transport & logistics | 2025 |
| Marvl Accounting Ltd | Professional & scientific | 2025 |
| Marwari Holdings Limited | Financial services | 2016 |
| Mary KAY Glamour Limited | Health & social care | 2025 |
| MAS SPV 2 Ltd | Real estate | 2024 |
| MAS SPV 3 Ltd | Real estate | 2024 |
| MAS SPV Ltd | Real estate | 2023 |
| Mason's Pride Group Limited | Financial services | 2022 |
| Mason's Pride Limited | Construction | 2019 |
| Mason's Pride Properties Limited | Real estate | 2022 |
| Masta Global Ltd | Professional & scientific | 2021 |
| Master Tattooers Limited | Other services | 2014 |
| Masterfix Maintenance Solutions Ltd | Manufacturing | 2024 |
| Masters Tennis Academy Limited | Arts & recreation | 2020 |
| Masterstroke Paintworks Ltd | Construction | 2025 |
| Materium Limited | Information & communication | 2025 |
| Matt Rendering Ltd | Construction | 2024 |
| Matterhorn Watch Company Ltd | Wholesale & retail | 2021 |
| Maurice's Jubilee Limited | Information & communication | 2025 |
| Maveric Systems Limited | Information & communication | 2015 |
| MAX Assets Ltd | Extraterritorial | 2022 |
| Maxcare London Limited | Health & social care | 2023 |
| Maxmedic London Limited | Health & social care | 2023 |
| Maxsol Assets Ltd | Real estate | 2023 |
| May's Property Solutions Limited | Real estate | 2021 |
| Maya Tandoori (Trading) Limited | Hospitality | 2023 |
| Maya Tandoori Limited | Hospitality | 2023 |
| Maylen Properties Ltd | Real estate | 2023 |
| Maynard Builders Ltd | Construction | 2026 |
| Mayplace Carpets Limited | Wholesale & retail | 2004 |
| Mayplace Investments Limited | Real estate | 2022 |
| Mazino (UK) Limited | Health & social care | 2010 |
| MB Axiom Consultancy Services Ltd | Professional & scientific | 2018 |
| MBL Mechanical and Electrical Ltd | Construction | 2024 |
| MC Business Solutions Limited | Professional & scientific | 2012 |
| MC Decoration Limited | Construction | 2024 |
| Mcbooth Ltd | Real estate | 2017 |
| Mcoc Properties Limited | Real estate | 2018 |
| MCR Mechanical Ltd | Construction | 2024 |
| MDI Contractors Limited | Construction | 2014 |
| Mdpm Productions Ltd | Information & communication | 2024 |
| MDW Consultancy Limited | Information & communication | 2005 |
| Mdyn Limited | Public administration | 2023 |
| ME Encanta Jewellery Limited | Wholesale & retail | 2007 |
| ME Energy Consulting Ltd | Professional & scientific | 2024 |
| Me-Av Limited | Professional & scientific | 2008 |
| Measured Boards Ltd | Professional & scientific | 2025 |
| Measured Quantity Surveying Ltd | Professional & scientific | 2017 |
| Mechanical Installation Management Limited | Construction | 2017 |
| Media Strategies UK Limited | Professional & scientific | 2009 |
| Medipartner Ltd | Professional & scientific | 2020 |
| Medstrat Ltd | Administrative & support | 2017 |
| Megan C. I. Hawkey Limited | Financial services | 2025 |
| Megg Limited | Hospitality | 2022 |
| Mel's Homes Ltd | Real estate | 2021 |
| Memo GUL Ltd | Hospitality | 2025 |
| Mera Court Management Limited | Households | 2025 |
| Merch Imprint Ltd | Manufacturing | 2026 |
| Mercury Drop Ltd | Construction | 2023 |
| Merriman Marine Services Ltd. | Manufacturing | 2018 |
| Mersham Road Shared Ownership Ltd | Financial services | 2021 |
| MET - TEC Roofing Ltd | Construction | 2024 |
| Meta Alpha Gamma Capital Limited | Financial services | 2021 |
| Metan Limited | Health & social care | 2014 |
| Metro Timber and Sheet Ltd | Wholesale & retail | 2024 |
| Metrorail Consulting Limited | Transport & logistics | 2023 |
| Metrro Properties Ltd | Real estate | 2018 |
| MF & JS Limited | Wholesale & retail | 2024 |
| Mfrench Catering Limited | Hospitality | 2025 |
| MH Finance Limited | Financial services | 2024 |
| MH Professionals Ltd | Professional & scientific | 2017 |
| MH1 Studio Limited | Real estate | 2014 |
| MHH Associates Limited | Other services | 2020 |
| MI Pro Ltd | Construction | 2017 |
| MIA Education Ltd | Education | 2024 |
| Middlewich Locum Ltd | Health & social care | 2014 |
| Mightybee Limited | Wholesale & retail | 2014 |
| Mijito Limited | Hospitality | 2021 |