| Mark. Durugo | | 1998 |
| Markit Consultancy Limited | Information & communication | 1994 |
| Markmores Limited | Construction | 1984 |
| Markstart Ltd | Real estate | 2007 |
| Marmead Limited | Real estate | 1972 |
| Marna Ltd | Wholesale & retail | 2011 |
| Maroo Homes Limited | Real estate | 2003 |
| Marson Management Limited | Real estate | 2004 |
| Martin. Mcmahon | | 1998 |
| Marum Healthcare Ltd | Professional & scientific | 2002 |
| Marwood Management Limited | Financial services | 1993 |
| Mary Kelleher & Associates Ltd | Professional & scientific | 2002 |
| Marz Group (U.K) Ltd | Other services | 2016 |
| Mason Inn Limited | Hospitality | 2025 |
| Masons Pest Control Limited | Other services | 2002 |
| Mass Investments U.K. Ltd | Real estate | 2002 |
| Masterbuild (UK) Limited | Professional & scientific | 2005 |
| Matthew Smith Prosthetics Limited | Information & communication | 2010 |
| Mavtech Limited | Administrative & support | 2003 |
| MAX C and Company Limited | Health & social care | 2014 |
| MAX Fitness Limited | Arts & recreation | 2006 |
| Maxima Properties (Barmston) Limited | Real estate | 2007 |
| Maxima Properties (Holdings) Limited | Financial services | 2007 |
| MAY & Thomson Estates Limited | Real estate | 2019 |
| MAY & Thomson Property LLP | | 2019 |
| Mayan Vije Limited | Professional & scientific | 2004 |
| Mayflower Strategies Limited | Administrative & support | 2017 |
| Maygrove Limited | Construction | 2007 |
| Maylene Trajano Limited | Health & social care | 2015 |
| Mayne Build Limited | Extraterritorial | 2006 |
| Mayo Construction Limited | Construction | 2002 |
| Mayotte Limited | | 1981 |
| MBF Barbers Limited | Other services | 2017 |
| Mc-Gyver 23 Company Limited | Health & social care | 2012 |
| MCA Trade Ltd | Construction | 2016 |
| Mcavoy Property Development Ltd | Real estate | 2026 |
| Mccallum Consulting Limited | Information & communication | 1998 |
| Mccarthy Business Services Limited | Professional & scientific | 2006 |
| Mclintock Vehicle Management Limited | Administrative & support | 2000 |
| MD Digital Ltd | Information & communication | 2018 |
| MD Editing Ltd | Arts & recreation | 2015 |
| MDF Solutions Limited | Information & communication | 2000 |
| MDN Build Ltd | Construction | 2023 |
| Mears Property Finance Ltd | Financial services | 2025 |
| Medescene Limited | Health & social care | 2004 |
| Medi Aesthetix Limited | Wholesale & retail | 1998 |
| Media Wisdom Photography Ltd | Professional & scientific | 2004 |
| Medical Banks Software Limited | Information & communication | 2012 |
| Medicor (U.K.) | | 1997 |
| Medistar Limited | Real estate | 1979 |
| Meditec International England Limited | Wholesale & retail | 1991 |
| Medux UK Holdco Limited | Financial services | 2021 |
| Meera Developments Limited | Real estate | 1998 |
| Meera Properties Limited | Real estate | 2006 |
| Mega Trading & Services Limited | Wholesale & retail | 1997 |
| Meghani Properties Limited | Real estate | 2024 |
| Mehfil Foods Limited | Hospitality | 2005 |
| Mehfil Hotels Limited | Hospitality | 2018 |
| Memodale Limited | Financial services | 1996 |
| Memphis Recording Service Limited | Other services | 2005 |
| Mendall Medical Services Limited | Health & social care | 2010 |
| Mepco UK Limited | Professional & scientific | 2002 |
| Merchant Taylors' School | Education | 1997 |
| Mercia Estates Limited | Wholesale & retail | 2001 |
| Mercury Motors Limited | Wholesale & retail | 1941 |
| Merd Ltd | Health & social care | 2013 |
| Meridian Portfolio Limited | Real estate | 2004 |
| Merit Estate (UK) Limited | Real estate | 2006 |
| Meroma Consulting Ltd | Professional & scientific | 2002 |
| Meronpace Limited | Transport & logistics | 1992 |
| Mertila Limited | Professional & scientific | 2007 |
| Meshcomms Consulting Limited | Information & communication | 2008 |
| Meston Systems Limited | Information & communication | 1998 |
| Metair Mechanical Services Limited | Manufacturing | 2005 |
| Metalin Limited | Administrative & support | 1990 |
| Mewtat Limited | Real estate | 2000 |
| Mezzo Music Limited | Arts & recreation | 2000 |
| MF Marketing Limited | Financial services | 2009 |
| MF Promotions Ltd | Financial services | 2022 |
| MF Strategic Planning Ltd | Financial services | 2022 |
| MFJ Training Ltd | Administrative & support | 2020 |
| Mhpms Ltd | Real estate | 2002 |
| Miah Professional Corp Limited | Education | 2017 |
| Micas Training Ltd | Education | 2007 |
| Michael Dodd Media Limited | Administrative & support | 2007 |
| Michael. O'Dowd | | 1998 |
| Michigan Laundrette Limited | Other services | 2007 |
| Microage Computer Services Limited | Information & communication | 1982 |
| Microcare Corporation Limited | Information & communication | 1993 |
| Micronets Limited | Information & communication | 2006 |
| Micropower Products Limited | Professional & scientific | 2003 |
| Midax Ltd | Information & communication | 2007 |
| Middlesex Badminton Dome Limited | Arts & recreation | 2023 |
| Middlesex Electrical Ltd | Manufacturing | 2015 |
| Middlesex Estates Limited | Hospitality | 2002 |
| Middlesex Financial Services (2004) Limited | Real estate | 2004 |
| Middlesex Meat Company Limited | Wholesale & retail | 1972 |
| Middx Limited | Wholesale & retail | 2004 |
| Middx Tyres Limited | Wholesale & retail | 2000 |
| Mide Limited | Information & communication | 2004 |