| Mako Developments (Hastings) Limited | Construction | 2024 |
| Mako Developments Limited | Financial services | 2021 |
| Malcolm Chalk Limited | Construction | 2004 |
| Malthouse Management Limited | Households | 1997 |
| Mane Flux Services and Suppliers Limited | Administrative & support | 2026 |
| Maneso Crafts Ltd | Wholesale & retail | 2025 |
| Manlyn Ltd | Extraterritorial | 2023 |
| Manor Farm Foods Limited | Wholesale & retail | 2017 |
| Mantle (Abingdon) Limited | Real estate | 2018 |
| Mantle (Epping) Limited | Real estate | 2015 |
| Mantle (Woodside) Limited | Real estate | 2002 |
| Mantle Asset Management Ltd | Administrative & support | 2018 |
| Mantle Capital Management Limited | Administrative & support | 2005 |
| Mantle Group Holdings Limited | Real estate | 2026 |
| Mantle Space Limited | Administrative & support | 2011 |
| Manvix Ltd | Transport & logistics | 2025 |
| Many Hands Financial Services Limited | Financial services | 2022 |
| Maple Avenue Management Company Ltd. | Households | 2004 |
| Maplewood Independent Living Limited | Health & social care | 2012 |
| Maplewood Recruitment Ltd | Professional & scientific | 2008 |
| March Hill Consulting Limited | Professional & scientific | 2024 |
| Marimba World Chocolate Limited | Hospitality | 2008 |
| Marina Court (Brixham) Land Company Limited | Households | 1996 |
| Marisella Properties Ltd | Real estate | 2005 |
| Maritime Analysis Limited | Information & communication | 2015 |
| Mark Galloway Productions Limited | Information & communication | 2004 |
| Mark Harvey Holdings Limited | Real estate | 2020 |
| Mark LEE Consultants Limited | Professional & scientific | 2019 |
| Mark Stannard VFX Limited | Information & communication | 2020 |
| Markov Drylining Ltd | Construction | 2022 |
| Marks Heeley Limited | Professional & scientific | 2008 |
| Markwell Place Management Limited | Real estate | 2012 |
| Marlborough Properties (Herts) Limited | Real estate | 2024 |
| Marr LDN Limited | Wholesale & retail | 2025 |
| Marrakech OIL Ltd | Wholesale & retail | 2024 |
| Marsh Harrier Group Ltd | Construction | 2021 |
| Marshall Fire Limited | Professional & scientific | 2021 |
| Marshgate Developments Limited | Real estate | 1998 |
| Martins Housekeeping Ltd | Administrative & support | 2023 |
| Martyn Fiddler Customs Services Limited | Professional & scientific | 2018 |
| Martyn Fiddler Tax Limited | Financial services | 2016 |
| Marylebone Financial Services Ltd | Financial services | 2026 |
| Marylebone Mortgages Ltd | Financial services | 2020 |
| Masala Dining Ltd | Hospitality | 2019 |
| Maslen Group Ltd | Wholesale & retail | 2026 |
| Masons Arms Somerset Ltd | Hospitality | 2024 |
| Master of Trades Ltd | Construction | 2013 |
| Masterful Software Ltd | Information & communication | 2021 |
| Masucci Dwyer Enterprises Limited | Professional & scientific | 2017 |
| Matching 10K CIC | Arts & recreation | 2025 |
| Matching Floors Limited | Construction | 2009 |
| Maternity Matters Limited | Education | 2014 |
| Matlings Management Limited | Real estate | 2019 |
| Matt Oakes Limited | Information & communication | 2017 |
| Matthew D. Jones Limited | Real estate | 2021 |
| Matthews Park Electrical Limited | Construction | 2018 |
| Maxellia Limited | Professional & scientific | 2017 |
| Maximon Healthcare Ltd | Health & social care | 2024 |
| MAY & Co Property Limited | Real estate | 2024 |
| Mayan Tech Ltd | Information & communication | 2018 |
| Maycroft Estates Limited | Real estate | 2011 |
| Mayflower Property Investments Limited | Real estate | 2017 |
| Mayland Developments Ltd | Real estate | 2016 |
| Mayvine Brickwork Ltd | Construction | 2015 |
| Mayvine Construction Ltd | Construction | 2006 |
| Mazoe Road Ltd | Real estate | 2016 |
| MBM Trade Limited | Wholesale & retail | 2006 |
| Mbrc Construction Ltd | Construction | 2021 |
| Mccat Motorsport Ltd | Arts & recreation | 2020 |
| Mcclelland Global Developments Limited | Construction | 2024 |
| Mcclelland Global Limited | Construction | 2019 |
| Mcdonald Consulting Ltd | Financial services | 2018 |
| MCE Services Ltd. | Professional & scientific | 2017 |
| Mcglashan & Sons Roofing and Maintenance Ltd | Construction | 2024 |
| Mckenzie Art & Design Ltd | Wholesale & retail | 2021 |
| Mckenzie Financial Limited | Financial services | 2018 |
| Mclamb Ltd | Professional & scientific | 2017 |
| Mclean and Mclean Consultants Limited | Professional & scientific | 2013 |
| Mcleanit Ltd | Administrative & support | 2025 |
| MCM Group Services Ltd | Construction | 2023 |
| Mcmillans Engineering Limited | Manufacturing | 2012 |
| MCO Heating Services Limited | Construction | 2025 |
| MDC Resources Limited | Financial services | 2015 |
| MDG Creative Ltd | Arts & recreation | 2024 |
| Mdinga Limited | Construction | 2014 |
| Mdynamic Deals Limited | Wholesale & retail | 2024 |
| Meadow Fields Management Company Limited | Real estate | 2019 |
| Meadowgrove Limited | Real estate | 2020 |
| Meat & Chill Ltd | Hospitality | 2026 |
| Mebe Capital Ltd | Hospitality | 2023 |
| Mechon Aviation Services Ltd | Administrative & support | 2018 |
| Media Steps Consulting Limited | Professional & scientific | 2010 |
| Mediacre Ltd | Information & communication | 2022 |
| Medisys Diagnostics Consulting Ltd | Information & communication | 2026 |
| Medwin Holdings Ltd | Professional & scientific | 2026 |
| Mehs Food Ltd | Wholesale & retail | 2017 |
| Menu Solutions Limited | Wholesale & retail | 2021 |
| Merchant Payment Solutions Ltd | Other services | 2020 |
| Mergesite Property Management Limited | Households | 1992 |
| Meridian Residency Ltd | Real estate | 2024 |