| Masce Limited | Financial services | 2004 |
| Mase Property Management Ltd | Real estate | 2019 |
| Mash Healthcare Limited | Health & social care | 2012 |
| Mash Software Limited | Information & communication | 2014 |
| Maslow Oxygen Therapy Limited | Health & social care | 2025 |
| Mason B 2013 Limited | Professional & scientific | 2013 |
| Mason Property Solutions Ltd | Administrative & support | 2011 |
| Maspo Food Ltd | Wholesale & retail | 2021 |
| Maspo Food Trade Ltd | Wholesale & retail | 2016 |
| Massey Detailing Limited | Wholesale & retail | 2023 |
| Massfluence Ltd | Information & communication | 2019 |
| Mastercraft York Limited | Construction | 2023 |
| Masters Events Ltd | Administrative & support | 2023 |
| Mastery Limited | Health & social care | 2014 |
| Matbaz Trading Limited | Energy | 2025 |
| Matchez Limited | Administrative & support | 2025 |
| Matdoc Ltd | Professional & scientific | 2011 |
| Matheson Communications Limited | Wholesale & retail | 2018 |
| Mathewsons Auctions Ltd | Wholesale & retail | 2023 |
| Mathewsons Events Limited | Administrative & support | 2025 |
| Mathewsons Motorsport Limited | Wholesale & retail | 2023 |
| Mathias HV Ltd | Construction | 2020 |
| Mathswithsophie Ltd | Education | 2022 |
| Matmer Court (Freehold) Company Limited | Extraterritorial | 2014 |
| Matmer Court (Management) Company Limited | Households | 1990 |
| Matobo Properties Ltd | Real estate | 2023 |
| Matrix 92 Consulting Limited | Professional & scientific | 2014 |
| Matt Atkinson Business Consultancy Ltd | Professional & scientific | 2026 |
| Matt Couldry Limited | Health & social care | 2024 |
| Matt Thomson Decorators Limited | Construction | 2006 |
| Matthew Horrocks Limited | Administrative & support | 2007 |
| Matthew James Developments Limited | Construction | 2020 |
| Matts Metals Ltd | Water & waste | 2010 |
| Matty Bovan Limited | Extraterritorial | 2018 |
| Maul Limited | Financial services | 2019 |
| Maultby Bros | Real estate | 1982 |
| Maunders Homes (East Anglia) Limited | Extraterritorial | 1987 |
| Maunders Homes (Midlands) Limited | Extraterritorial | 1995 |
| Maunders Homes (North West) Limited | Extraterritorial | 1977 |
| Maunders Homes (South) Limited | Extraterritorial | 1977 |
| Maunders Inner City Limited | Extraterritorial | 1992 |
| Maunders Urban Renewal Limited | Extraterritorial | 1989 |
| Maundi Limited | Information & communication | 2013 |
| Maurice Sharp Funeral Directors Ltd | Other services | 2003 |
| Mauve Corporate Systems UK Limited | Professional & scientific | 1999 |
| Mavinto Limited | Wholesale & retail | 2019 |
| Mavnid Limited | Administrative & support | 2023 |
| Mavo Ltd | Wholesale & retail | 2019 |
| MAW Import Wheels Ltd | Wholesale & retail | 2026 |
| Mawson's Court Management Company Limited | Households | 2001 |
| Mawsons Court Freehold Ltd | Households | 2017 |
| MAX Car Care Limited | Wholesale & retail | 2016 |
| MAX PPF & Detailing Ltd | Wholesale & retail | 2025 |
| Maxi Engineering Ltd | Professional & scientific | 2026 |
| Maxi Living Ltd | Households | 2025 |
| Maxi's (Rotisserie) Limited | Wholesale & retail | 2003 |
| Maxi's (York) Limited | Hospitality | 1999 |
| Maxi's Express Ltd | Hospitality | 2026 |
| Maximalist Limited | Information & communication | 2024 |
| Maximise PM Limited | Manufacturing | 2016 |
| Maxlotte Logistics Ltd | Transport & logistics | 2024 |
| Maxwell & Kennedy Limited | Professional & scientific | 2015 |
| Maxwell Advisory Limited | Professional & scientific | 2025 |
| Maxwell G Developments Ltd | Construction | 2020 |
| Maxwell Scott Bags Limited | Wholesale & retail | 2013 |
| Maxwells York Ltd | Real estate | 2023 |
| Maxzero Games Ltd | Information & communication | 2024 |
| Mayclose Research Limited | Extraterritorial | 1969 |
| Mayfair Medicare Ltd | Health & social care | 2019 |
| Mayfield Grove Management Company Limited | Households | 1990 |
| Mayfield Nursery (York) Ltd | Agriculture & fishing | 2012 |
| Mayfield Property Management (York) Ltd | Real estate | 2021 |
| Mayo Avenue 1931 | Financial services | 2024 |
| Mayonnaise Treasure York Limited | Wholesale & retail | 2025 |
| Maypole Media (UK) Limited | Professional & scientific | 2008 |
| Mayworth Feltham Limited | Extraterritorial | 2026 |
| Mbat Global Ltd | Wholesale & retail | 2025 |
| MBB Investments (York) Ltd | Real estate | 2022 |
| MBF Advisory Ltd | Professional & scientific | 2024 |
| MBO Management Services Limited | Professional & scientific | 2012 |
| MBR Property Portfolio Ltd | Real estate | 2026 |
| MBW Property Finance Ltd | Financial services | 2026 |
| MC Accountancy Services Limited | Professional & scientific | 2020 |
| MC Marshall Farms Limited | Agriculture & fishing | 2020 |
| MC York Ltd | Wholesale & retail | 2024 |
| MC33 Limited | Wholesale & retail | 2026 |
| Mcbeath Beanland Limited | Real estate | 2006 |
| Mcbeath Property Consultancy Limited | Administrative & support | 2005 |
| Mcbride Partners Human Capital Limited | Administrative & support | 2014 |
| Mccallion Consulting Limited | Professional & scientific | 2025 |
| Mccarthy Holiday Cottages Ltd | Real estate | 2025 |
| Mccleary Medical Consultancy Ltd | Health & social care | 2019 |
| Mccombe Sports Consultancy Ltd | Arts & recreation | 2024 |
| Mccorrie Payroll Services Ltd | Professional & scientific | 2023 |
| MCE Collections Ltd | Wholesale & retail | 2025 |
| Mceneaney Consulting (Legal) Ltd | Administrative & support | 2023 |
| MCG Change Management Ltd | Professional & scientific | 2019 |
| Mchandy Plastering and Decorating Limited | Construction | 2016 |
| Mcinnes Cook Light Limited | Wholesale & retail | 2015 |
| Mcinnes Cook Limited | Wholesale & retail | 2006 |