| Mavio Limited | Households | 1975 |
| MAX Barbers Ltd | Other services | 2013 |
| Maximus Media Ltd | Information & communication | 2024 |
| Maycon Consulting Limited | Information & communication | 2016 |
| Mayfield Land Management Ltd | Households | 2002 |
| Mayford Joinery Limited | Manufacturing | 2007 |
| Mayshill 1 Limited | Professional & scientific | 2024 |
| Mayu Properties Ltd | Real estate | 2025 |
| Mazda Choice Limited | Extraterritorial | 1996 |
| Mazda Speed Limited | Extraterritorial | 1996 |
| MBC Innovations Ltd. | Wholesale & retail | 2008 |
| Mbci Group Limited | Wholesale & retail | 2020 |
| MBM Omega Holdings Limited | Professional & scientific | 2009 |
| MBM Omega Limited | Administrative & support | 1993 |
| Mbuild Design Ltd | Construction | 2020 |
| MCB Partners Consulting Limited | Professional & scientific | 2013 |
| Mccarthy Technology Services Limited | Information & communication | 2006 |
| Mcfinity Limited | Professional & scientific | 2020 |
| Mckinney Consulting Limited | Professional & scientific | 2007 |
| Mcnorton Limited | Construction | 2019 |
| MD Transportation Ltd | Transport & logistics | 2024 |
| MDH Property Solutions Limited | Construction | 2015 |
| ME3 Consulting Ltd | Professional & scientific | 2016 |
| Meadow Way Residents Association Limited | Households | 1987 |
| Meadway Homes (Kempton) Ltd | Real estate | 2020 |
| Meadway Homes (Woodlands Lane) Ltd | Construction | 2022 |
| Meadway Homes Limited | Real estate | 2009 |
| Meadway Private Clients (Construction) Ltd | Construction | 2016 |
| Mechanical Air Supplies Limited | Wholesale & retail | 1992 |
| Media Music Limited | Information & communication | 1994 |
| Media Plan Limited | Professional & scientific | 2014 |
| Media Script Checks Limited | Information & communication | 2011 |
| Mediant Cambridge Limited | Professional & scientific | 2001 |
| Medukcare Recruitment Limited | Health & social care | 2016 |
| Medway NCE Draughting Limited | Extraterritorial | 2007 |
| Meelas World UK Limited | Other services | 2024 |
| Mega Productions Limited | Information & communication | 2010 |
| Megannons Property Care Limited | Construction | 2024 |
| Megaw Partners Ltd | Professional & scientific | 2026 |
| Meiwood Limited | Information & communication | 2023 |
| Melrose Ceremonies and Event Hire Ltd | Administrative & support | 2025 |
| Melton Court Management Limited | Households | 1986 |
| Memforest Limited | Information & communication | 1978 |
| Memto Limited | Administrative & support | 2026 |
| Merel Rehorst-Smith Limited | Professional & scientific | 2015 |
| Merits Made Limited | Information & communication | 2025 |
| Mermaid Engineering Consultants Limited | Professional & scientific | 2005 |
| Merrow Court Residents Association Limited | Households | 1959 |
| Merry House Malaysia Ltd | Hospitality | 2019 |
| MET Capital Management LLP | | 2009 |
| MET Securities LLP | | 2011 |
| Meta Trade Investment Portfolio Management Services Ltd | Professional & scientific | 2025 |
| Metaconnections Limited | Information & communication | 2002 |
| Metin Alim Limited | Information & communication | 2011 |
| Mforge Ltd | Wholesale & retail | 2026 |
| MGA Healthcare Ltd | Health & social care | 2026 |
| MGA United Ltd | Administrative & support | 2022 |
| Miami Funk Ltd | Information & communication | 2025 |
| Michael Wagstaff & Associates LLP | | 2009 |
| Michelle Germain Wealth Ltd | Financial services | 2023 |
| Mickleham Downs House Limited | Real estate | 2016 |
| Microstation Ltd | Water & waste | 2011 |
| Middle Farm Close Management Company Limited | Households | 1995 |
| Midgarth Residents Company Limited | Households | 1994 |
| Midland Tool Hire Limited | Professional & scientific | 1992 |
| Midnight Movement Ltd | Professional & scientific | 2017 |
| Mihai Construction Ltd | Construction | 2026 |
| Milestone House (Freehold) Limited | Households | 2013 |
| Mill House Advisory Limited | Professional & scientific | 2026 |
| Miller FOX HR Services Limited | Administrative & support | 2018 |
| Millionaire Competitions Ltd | Arts & recreation | 2026 |
| Millionaire Competitions Racing Ltd | Other services | 2026 |
| Mills I Limited | Wholesale & retail | 2023 |
| Millside Court Limited | Households | 1973 |
| Milwyn Casting Limited | Manufacturing | 2018 |
| Mimosa Landscapes Limited | Administrative & support | 2001 |
| Mindwave Digital Limited | Information & communication | 2015 |
| Minerva Rock Limited | Health & social care | 2010 |
| Mini Memento Ltd | Manufacturing | 2020 |
| Mint Coffee Shop Ltd | Hospitality | 2025 |
| Mioc Consulting Limited | Professional & scientific | 2020 |
| Mirror by Design Ltd | Manufacturing | 2015 |
| Mistress Murders Ltd | Arts & recreation | 2020 |
| Mitchell & Sons Limited | Wholesale & retail | 2007 |
| MJ Watkins Electrical Limited | Construction | 2023 |
| MJM Timeout Properties LLP | | 2022 |
| MK IP Works Ltd | Hospitality | 2010 |
| MKB Fire and Security Ltd | Public administration | 2025 |
| Mkhonzeni Healthcare Limited | Health & social care | 2015 |
| MKS Contract Services Limited | Construction | 2012 |
| Mlcbam Ltd | Transport & logistics | 2025 |
| MLT Property Ltd | Construction | 2024 |
| Mmpv Limited | Professional & scientific | 2019 |
| Mobivape Ltd | Wholesale & retail | 2016 |
| Model Financial Solutions Limited | Financial services | 2012 |
| Mole Bridge Management Limited | Households | 2014 |
| Mole Hill Creative Services Limited | Professional & scientific | 2014 |
| Mole Valley Pest Control Limited | Other services | 2015 |
| Molebridge Practice LP | | 2019 |
| Moletech Software Solutions Limited | Information & communication | 2025 |