| Manuscripti Limited | Information & communication | 2002 |
| Maplefields Community Centre | Extraterritorial | 2017 |
| Maqsood Ltd | Health & social care | 2012 |
| Marauding Mustangs Limited | Arts & recreation | 2016 |
| Marcus Cunnington Limited | Administrative & support | 2012 |
| Marcus Delo Creative Limited | Information & communication | 2020 |
| Margrace Sterile Limited | Extraterritorial | 2021 |
| Maridec Ltd | Construction | 2016 |
| Mark IT Buddy Limited | Construction | 2023 |
| Mark James Home Improvements Ltd | Construction | 2025 |
| Mark Kerfoot Masonry Ltd | Administrative & support | 2016 |
| Mark Nicholson Property Finder Limited | Real estate | 2025 |
| Mark Riccioni Imaging Ltd | Professional & scientific | 2014 |
| Mark Tierney Limited | Construction | 2008 |
| Mark Watts Limited | Wholesale & retail | 2006 |
| MARK2 Solutions Ltd | Professional & scientific | 2007 |
| Market Hill Developments Ltd | Construction | 2021 |
| Marketing 4 Results Limited | Professional & scientific | 2005 |
| Marketing Mind Intelligence Ltd | Professional & scientific | 2017 |
| Marquee Holdings Ltd | Financial services | 2024 |
| Marsden-Findlay Productions Limited | Professional & scientific | 2008 |
| Marsdons Inns Limited | Hospitality | 2009 |
| Marsh Industries Limited | Manufacturing | 2004 |
| Marshall Piano Services Limited | Manufacturing | 2013 |
| Marshan Limited | Hospitality | 2021 |
| Martin Brothers Curtains Limited | Manufacturing | 1976 |
| Martin Ceramics Limited | Administrative & support | 2008 |
| Martin Kucar Ltd | Transport & logistics | 2019 |
| Martin Richartz Ltd | Professional & scientific | 2012 |
| Martyn Walker Driver Hire Ltd | Transport & logistics | 2016 |
| Maruthoor Travel Ltd. | Administrative & support | 2024 |
| Marval Group Limited | Information & communication | 2007 |
| Marval Investments Limited | Financial services | 2017 |
| Marvick Enterprise Ltd | Hospitality | 2012 |
| Marzec Associates Limited | Professional & scientific | 2002 |
| MAS Farms Ltd | Agriculture & fishing | 2004 |
| Masafina Limited | Hospitality | 2022 |
| Mase Electrical Installations Limited | Energy | 2022 |
| Maskearaid Limited | Wholesale & retail | 2016 |
| Massala Junction Ltd | Hospitality | 2024 |
| Massy Trading Limited | Other services | 2016 |
| Master Mech Limited | Wholesale & retail | 2023 |
| Masterman Plumbing and Heating Ltd | Construction | 2026 |
| Masters Sales Training Limited | Professional & scientific | 2010 |
| MAT Installations Limited | Administrative & support | 2023 |
| Mateas Transport Ltd | Transport & logistics | 2025 |
| Material Girl Fine Furnishings Ltd | Manufacturing | 2010 |
| Math Surveying Limited | Professional & scientific | 2020 |
| Matrix Gymnastics Academy Limited | Arts & recreation | 2017 |
| Matrix Inks Ltd | Wholesale & retail | 2020 |
| Matrix Orbis Limited | Information & communication | 2026 |
| Matrix Orbis Sovereign Ltd | Information & communication | 2026 |
| Matt Johnson Independent Mortgage Advice Ltd | Financial services | 2021 |
| Matthew Coltman Bowmaker Limited | Manufacturing | 2012 |
| MAW Building & Roofing Limited | Construction | 2005 |
| MAW Rentals Limited | Real estate | 2021 |
| Mawat Developments Ltd | Households | 2024 |
| Mawsley Garden Maintenance Ltd | Administrative & support | 2020 |
| Mawsley Lodge Limited | Administrative & support | 2015 |
| Mawsley Scaffolding Ltd | Construction | 2026 |
| Mawsley Villagers Association Limited | Other services | 2006 |
| Maxco Projects Ltd | Wholesale & retail | 2025 |
| Maxentra Limited | Construction | 2019 |
| Maxim Growth Limited | Professional & scientific | 2023 |
| Maximus 567 Ltd | Wholesale & retail | 2021 |
| Maxwill UK Limited | Wholesale & retail | 2024 |
| Maybury Motor Company Ltd | Wholesale & retail | 2010 |
| Mayes GAS Services Limited | Construction | 2019 |
| Mayford Place Ltd | Construction | 2026 |
| Mayur Shah Health Ltd | Health & social care | 2012 |
| Maziak Clothing Ltd | Wholesale & retail | 2025 |
| Maziak Design Ltd | Professional & scientific | 2021 |
| Maziak Properties Holdings Ltd | Financial services | 2022 |
| Maziak Properties Ltd | Real estate | 2022 |
| Mazzone Construction Ltd | Construction | 2023 |
| MB HV Engineering Limited | Construction | 2009 |
| Mbangels Ltd | Administrative & support | 2020 |
| MBJ Properties Ltd | Real estate | 2014 |
| Mbr-Uk Ltd | Information & communication | 2021 |
| MC Building & Paving Ltd | Administrative & support | 2025 |
| MC Headland (Thatchers) Limited | Construction | 2002 |
| MC Moving Ltd | Transport & logistics | 2025 |
| MC Perkins Joinery Limited | Manufacturing | 2014 |
| MC Technical Services Limited | Manufacturing | 2000 |
| Mccabe & Barton Limited | Administrative & support | 2000 |
| Mccallum Consultancy Limited | Professional & scientific | 2022 |
| Mcgowan Investments Limited | Real estate | 1995 |
| Mcgregor Travel Limited | Administrative & support | 2025 |
| Mckee Velo and Automotive Limited | Wholesale & retail | 2015 |
| Mclaren Carpentry Limited | Manufacturing | 2023 |
| Mclaren-Martinez Limited | Hospitality | 2011 |
| MCM Environmental Ltd | Professional & scientific | 2021 |
| Mcmtiling Ltd | Construction | 2025 |
| Mczara Services Limited | Construction | 2026 |
| MD Electrical Solutions Limited | Administrative & support | 2014 |
| MD Mortgage & Protection Ltd | Financial services | 2011 |
| MDA Courier Ltd | Transport & logistics | 2026 |
| MDH (Tcfo) Professional Services Limited | Professional & scientific | 2026 |
| Mdml Properties Ltd | Real estate | 2026 |
| MDS Group Investments Limited | Financial services | 2023 |