| Mayfords Limited | Manufacturing | 2002 |
| Mayhurst Avenue (Management) Company Limited | Real estate | 2002 |
| Mbms Services Ltd | Professional & scientific | 2003 |
| MC Quality Management Ltd | Administrative & support | 2008 |
| Mcbain Consulting Limited | Professional & scientific | 2026 |
| Mcbrown Ltd | Construction | 2005 |
| Mccarthy Cars (Croydon) Limited | Wholesale & retail | 2002 |
| Mcdaniel Woolf Limited | Professional & scientific | 1995 |
| Mcdonnell Investments Limited | Real estate | 2004 |
| Mcdragon 888 Ltd | Hospitality | 2022 |
| Mcfarlane Consultancy Ltd | Administrative & support | 2018 |
| Mcfarlane Finance Consultants Limited | Professional & scientific | 2007 |
| Mcgowen Rose Associates Ltd | Professional & scientific | 1999 |
| Mckinven Limited | Professional & scientific | 2006 |
| Mclarens Properties Limited | Real estate | 2011 |
| Mcleod Kerr Ltd | Professional & scientific | 2006 |
| MDM Vision Care Limited | Administrative & support | 2007 |
| Meacat Limited | Professional & scientific | 2001 |
| Meadcroft Residents Company Limited | Professional & scientific | 1998 |
| Meadow Management Limited | Households | 2001 |
| Meadowbank Management Company Limited | Professional & scientific | 1983 |
| Mealfirst Ltd | Hospitality | 2013 |
| Mecron Solutions Limited | Extraterritorial | 1995 |
| Medi Travel Cover Limited | Financial services | 2002 |
| Media Alliance Limited | Arts & recreation | 1985 |
| Medialliance Limited | Professional & scientific | 2003 |
| Mediamorphosis Limited | Information & communication | 2001 |
| Mediazest International Ltd | Other services | 1975 |
| Mediazest PLC | Professional & scientific | 2004 |
| Medical Services and Equipment (M.E.) Limited | Health & social care | 1982 |
| Medico Legal Direct Limited | Health & social care | 2007 |
| Medius Ltd | Information & communication | 2007 |
| Medlar Estates Limited | Real estate | 2002 |
| Medlet Limited | Real estate | 2000 |
| Medtrade Limited | Health & social care | 2004 |
| MEE Care Ltd | Health & social care | 2022 |
| Meedsi | Health & social care | 2019 |
| Meejana Limited | Hospitality | 2005 |
| Meewella Limited | Information & communication | 2008 |
| MEG Consultancy & Advisory Ltd | Information & communication | 2018 |
| Mega Kitchens Limited | Wholesale & retail | 2005 |
| Mega Scoop Circle Limited | Administrative & support | 2005 |
| Megador | | 1987 |
| Mehan Properties Limited | Construction | 1961 |
| Meikles Limited | Professional & scientific | 1999 |
| Melanie Jane Management Limited | Administrative & support | 2011 |
| Melbamain Limited | Real estate | 1974 |
| Melfort House Management Company Limited | Real estate | 2020 |
| Melo & Melo S Ltd | Construction | 2016 |
| Melodisc Music Limited | Information & communication | 1966 |
| Meltones Limited | Wholesale & retail | 1989 |
| Melville & Co (East Molesey) Limited | Real estate | 2001 |
| Melville Properties (UK) Limited | Real estate | 2004 |
| Memoryrental.Com Ltd | Other services | 2025 |
| Menaissence Ltd | Professional & scientific | 2004 |
| Merchant Seamen's WAR Memorial Society (Incorporated)(The) | Hospitality | 1947 |
| Mercury Microwave Ovens Limited | | 1969 |
| Merritt-Harrison Catering Consultancy Limited | Professional & scientific | 1995 |
| Merrivale Marketing Limited | Professional & scientific | 1999 |
| Merstham Football and Social Club Ltd | Arts & recreation | 2003 |
| Metcomp Limited | Information & communication | 1985 |
| Metric Property Management Ltd | Real estate | 2025 |
| Metro Security (UK) Limited | Administrative & support | 1993 |
| Metsuke (Property Developments) Limited | | 1974 |
| Metta Logic Limited | Information & communication | 1996 |
| Metzer Consulting Limited | Professional & scientific | 2007 |
| Meybush Finance Limited | Wholesale & retail | 1971 |
| MFX Capital Ltd | Financial services | 2020 |
| MG Precision Engineering (UK) Limited | Manufacturing | 2003 |
| MG Tyres Ltd | Wholesale & retail | 2023 |
| MGC (Contracts) Limited | Construction | 1998 |
| MGK Enterprises Limited | Hospitality | 2003 |
| MGM Residentials Limited | Households | 2007 |
| MGW Holdings Limited | Real estate | 1968 |
| MI Amor Beauty Limited | Other services | 2025 |
| MI1LION Ltd | Information & communication | 2025 |
| Miadork Limited | | 1979 |
| MIC Developments Limited | Construction | 1995 |
| Micaela Cianci Limited | Arts & recreation | 2002 |
| Michael Burke & Company Limited | Professional & scientific | 2005 |
| Michael Byrd Violins Limited | Wholesale & retail | 2006 |
| Michael C. Doughty Limited | Financial services | 1974 |
| Michael Everett & Co. Limited | Real estate | 2001 |
| Michael Lane Decorative Services Limited | Construction | 2003 |
| Michael Mccarthy Sound Design Limited | Information & communication | 2008 |
| Michael Melia & Company Limited | | 1976 |
| Michael Rogers (Surveyors) Limited | Extraterritorial | 1990 |
| Michael Rogers Property Management Limited | Real estate | 1999 |
| Micklefield School (Reigate) Limited | Extraterritorial | 1960 |
| Micret Property Co.Limited | Real estate | 1954 |
| Micro Minerva Consultants Limited | Information & communication | 1990 |
| Microwave Kitchen Limited | | 1980 |
| Midas Wealth Management Ltd | Financial services | 2003 |
| Middle Farm Place Management Company Limited | Households | 1989 |
| Middleton Mount Property Company Limited | Households | 1984 |
| Midsummer Court Harrow RTM Company Limited | Households | 2025 |
| Mightclaim Limited | Professional & scientific | 1991 |
| Mikifin Limited | Professional & scientific | 2005 |
| Mikisha Subs Ltd | Hospitality | 2025 |
| Milan Patel Limited | Health & social care | 2005 |