| MAX Your Finance Limited | Professional & scientific | 2015 |
| MAX Your Web Limited | Information & communication | 2012 |
| Maxchinauk Ltd | Wholesale & retail | 2024 |
| Maxelyn Property Ltd | Real estate | 2026 |
| Mayfair & ST. James's Association Limited | Other services | 1951 |
| Mayk Design Ltd | Professional & scientific | 2025 |
| Mayuran Siva Limited | Professional & scientific | 2014 |
| MAZ Grill Ltd | Hospitality | 2017 |
| Mazza Consultancy Services Ltd | Information & communication | 2018 |
| MB Maintenance Services Ltd | Construction | 2025 |
| MC & MK Properties Ltd | Real estate | 2012 |
| Mcarthur Campbell Holdings Limited | Health & social care | 2014 |
| Mcdetak Ltd | Wholesale & retail | 2023 |
| MCG Installations Limited | Construction | 2026 |
| Mcgeo Ltd | Wholesale & retail | 2024 |
| Mckenna Force Ltd | Construction | 2020 |
| Md.Ch Contractors Ltd | Construction | 2025 |
| Mdermauthority Aesthetics Ltd | Health & social care | 2023 |
| MDG Brickwork & Building Limited | Construction | 2015 |
| Mead Management Company (Wallington) Limited | Households | 1998 |
| Meadows Global Tradings Ltd | Wholesale & retail | 2012 |
| MEC and Sons Ltd | Wholesale & retail | 2024 |
| Medibaba Ltd | Real estate | 2020 |
| Medica 1971 Limited | Health & social care | 2011 |
| Medicada Company Limited | Professional & scientific | 2024 |
| Medicalsupportunion Ltd | Administrative & support | 2012 |
| Medicines 4 Health Ltd | Health & social care | 2012 |
| Medveda Ltd | Administrative & support | 2024 |
| MEE & CEE Family Consultancy Limited | Professional & scientific | 2020 |
| Meenu Prav Ltd | Real estate | 2023 |
| Meenu Trading Limited | Wholesale & retail | 2019 |
| Mega Motor Store Limited | Wholesale & retail | 2021 |
| Meher Investments Limited | Real estate | 2024 |
| Meite Services Limited | Construction | 2025 |
| Melissa Budasz Limited | Professional & scientific | 2018 |
| Melrose ROW Ltd | Other services | 2020 |
| MEN & Van Ltd | Transport & logistics | 2026 |
| Mentor Lock Ltd | Wholesale & retail | 2010 |
| Merclara Beebs Limited | Real estate | 2021 |
| Meretune Management (Falcon) Limited | Households | 1981 |
| Merrett Design & Build Limited | Construction | 2020 |
| Merrett Plumbing & Heating Services Limited | Construction | 2018 |
| MES Electrical Surrey Ltd | Construction | 2025 |
| Method Collective Ltd | Information & communication | 2026 |
| METO61 Limited | Construction | 2014 |
| Metric Construction Scotland Limited | Construction | 2014 |
| Metropolitan Mews Limited | Extraterritorial | 2012 |
| MEX Strength Ltd | Information & communication | 2022 |
| MF Machinery Limited | Manufacturing | 2023 |
| MFA Logistics Ltd | Transport & logistics | 2014 |
| MG Acting Services Ltd | Arts & recreation | 2013 |
| MG Radio Ltd | Information & communication | 2024 |
| Mg&D Ltd | Real estate | 2024 |
| Mgaq Ltd | Real estate | 2018 |
| MGM Building & Maintenance Limited | Construction | 2019 |
| MGM Wealth Ltd | Real estate | 2025 |
| Mheg 5 Ltd | Real estate | 2019 |
| MHG Heating Ltd | Manufacturing | 2007 |
| MHG Legal Limited | Professional & scientific | 2018 |
| Miami Health Club Limited | Other services | 1997 |
| Miami House Freehold Limited | Households | 2020 |
| Michael Burch Consulting Ltd | Wholesale & retail | 2016 |
| Michaela Nuttall Limited | Education | 2012 |
| Micro Chems Facilities Limited | Wholesale & retail | 1998 |
| MIK Services Limited | Professional & scientific | 2019 |
| Mika Horizons Limited | Public administration | 2026 |
| Mikus Consulting Limited | Professional & scientific | 2020 |
| Milanmade Ltd | Manufacturing | 2025 |
| Millar Factory Limited | Information & communication | 2013 |
| Millett & Williamson Ltd | Real estate | 2023 |
| Million & 1 Ltd | Arts & recreation | 2023 |
| Miloh Limited | Real estate | 2025 |
| Mimi & Rafi Limited | Information & communication | 2009 |
| Mimm's Caring Angels Limited | Health & social care | 2017 |
| Mina Wallington Properties Ltd | Real estate | 2025 |
| Mind Science & Super Natural 1112 AI Sciences Ltd | Information & communication | 2026 |
| Mindforward Alliance C.I.C. | Education | 2019 |
| Minds Technologies Limited | Information & communication | 2013 |
| Mini Refs Limited | Arts & recreation | 2009 |
| Mininat Limited | Real estate | 2020 |
| Minky Subs Ltd | Hospitality | 2025 |
| Mireille B Limited | Administrative & support | 2013 |
| Mist Ventures Limited | Hospitality | 2025 |
| Miweb Limited | Professional & scientific | 2017 |
| MJ Sanding Ltd | Construction | 2017 |
| MK Beauty Clinic Ltd | Other services | 2017 |
| MK Retail Trading Limited | Wholesale & retail | 2021 |
| MK Veasey Electrical Limited | Construction | 2015 |
| MKA Investments Limited | Real estate | 2019 |
| Mkango & Associates Ltd | Professional & scientific | 2026 |
| MKB Academy Ltd | Arts & recreation | 2017 |
| Mkvs Consultancy Limited | Professional & scientific | 2025 |
| MLM Property Group Ltd | Real estate | 2023 |
| MMM Consulting Engineers Ltd | Construction | 2025 |
| MMM Services Limited | Transport & logistics | 2026 |
| MMS SERV1CE Ltd | Transport & logistics | 2024 |
| MNB Paving Limited | Construction | 1997 |
| MO Choy Design Limited | Arts & recreation | 2004 |
| MO Delivery Ltd | Transport & logistics | 2025 |
| Mobysign Limited | Information & communication | 2014 |