| Mandale Mills Management Company Limited | Households | 2002 |
| Mandeville Place (ELY) Management Company Limited | Households | 2000 |
| Manford Park Management Company Limited | Households | 1999 |
| Manifestinfr Ltd | Information & communication | 2026 |
| Manor Court (Cheshunt) Property Management Company Limited | Households | 1994 |
| Manor Gardens Residents Company Limited | Households | 2001 |
| Manor Park Sprowston Residents Management Company Limited | Households | 2015 |
| Manor Place Management Company (Angmering) Limited | Real estate | 2023 |
| Manor Woods (Kirkbymoorside) Management Company Limited | Households | 2020 |
| Maple 10 Ltd | Financial services | 2019 |
| Maple 4 Ltd | Financial services | 2018 |
| Maple Court White Moss Management Company Limited | Real estate | 2007 |
| MAR Property Investments Ltd | Real estate | 2022 |
| Marble House (Ebbsfleet) Management Company Limited | Households | 2025 |
| Marcello TYE (Felsted) Management Company Limited | Households | 2004 |
| Marco Impex Ltd | Wholesale & retail | 2019 |
| Marcus Bohn Associates Limited | Other services | 2016 |
| Mare Terra Limited | Wholesale & retail | 2014 |
| Maridin Investments Limited | Real estate | 2019 |
| Marine Details Ltd | Manufacturing | 2021 |
| Mariners Point (Hartlepool) Management Company Limited | Households | 2002 |
| Maritime House (Woolwich) RTM Company Limited | Households | 2013 |
| Maritime House Residents Association Limited | Households | 1997 |
| Mark House (Poundbury) Management Company Limited | Households | 2016 |
| Mark Thomas Services Ltd | Construction | 2024 |
| Market Court Management Hoddesdon Ltd | Households | 2015 |
| Marmoran (UK) Limited | Construction | 2009 |
| Martello Lakes (Barratt) Resident Management Company Limited | Households | 2016 |
| Martello Lakes (Hythe) Residents Management Company Limited | Households | 2022 |
| Martin Lukac Ltd | Construction | 2012 |
| Martingale Chase (Newbury) Management Company Limited | Households | 2004 |
| Martini Mandate Limited | Professional & scientific | 2014 |
| Martorana Fighetto Ltd | Wholesale & retail | 2019 |
| Martorana Investments Limited | Real estate | 2017 |
| Mary & Petry Ltd | Transport & logistics | 2025 |
| Maskan Limited | Professional & scientific | 2011 |
| Masterclassing Limited | Administrative & support | 2014 |
| Matcham Signs Limited | Manufacturing | 2004 |
| Matinicus Pharma Limited | Professional & scientific | 2022 |
| Mavin Communications Ltd | Professional & scientific | 2025 |
| MAX Investment Group Limited | Real estate | 2022 |
| MAX Metal Works Limited | Administrative & support | 2020 |
| MAX My BIZ Limited | Professional & scientific | 2016 |
| Maxall Ltd | Construction | 2023 |
| Maxi Travel Ltd | Transport & logistics | 2014 |
| Maxibus Travel Ltd | Transport & logistics | 2019 |
| Maxicad Limited | Administrative & support | 2014 |
| Maya Building Construction Limited | Construction | 2019 |
| Mayfair International Realty Limited | Extraterritorial | 2005 |
| Mayfair Media & Marketing Limited | Extraterritorial | 1998 |
| Mayfair Office Limited | Real estate | 1995 |
| Mayflower Court (Flats) Management Company Limited | Households | 2001 |
| Mayhem Creative Ltd | Administrative & support | 2025 |
| Maypole Green Residents Company Limited | Households | 2001 |
| Mbcb Property Holdings Ltd | Real estate | 2024 |
| MBE Property Services Limited | Administrative & support | 2017 |
| MBG Logistics Ltd | Transport & logistics | 2016 |
| Mbsc Asset Management Ltd | Administrative & support | 2025 |
| MC Brothers Ltd | Construction | 1995 |
| MCA Distribution and Storage Limited | Transport & logistics | 2025 |
| Mccorquodale Gardens Management Company Limited | Households | 2015 |
| Mcdm Group Limited | Wholesale & retail | 2023 |
| Mckinney's TE & Coffi Ltd | Hospitality | 2024 |
| Mcpestcontrol Limited | Administrative & support | 2024 |
| Mcrae's Building and Maintenance Limited | Real estate | 2025 |
| Mcrae's Sales and Lettings Limited | Real estate | 2025 |
| ME 2 U Logistics Ltd | Transport & logistics | 2015 |
| ME Oils Limited | Other services | 2022 |
| Mead (Merton) Management Company Limited | Households | 1986 |
| Meadow Brook Chalgrove Development Limited | Households | 2025 |
| Meadow View (Oldham) Management Company Limited | Households | 2015 |
| Meadows Green (Mundella Centre) Management Company Limited | Households | 2021 |
| Meadowside (East Ardsley) Management Limited | Households | 2005 |
| Meads (NO 2) Residents Company Limited | Households | 2002 |
| Mechanical Control Ltd | Energy | 2010 |
| Mectric Holdings Ltd | Financial services | 2024 |
| Mectric Services Ltd | Construction | 2024 |
| Mectric Solutions Ltd | Construction | 2006 |
| Medinova Consulting Ltd | Professional & scientific | 2024 |
| Mega at the Café Limited | Hospitality | 2015 |
| MEK Design Engineers Ltd | Professional & scientific | 2006 |
| Melder Consulting Limited | Professional & scientific | 2023 |
| Melford Court Management Company Limited | Households | 2004 |
| Melly CNZ Ltd | Other services | 2026 |
| Mems of Enfield Limited | Wholesale & retail | 2024 |
| Memur Foods Ltd | Hospitality | 2024 |
| Mercantile MET Tech Limited | Manufacturing | 2003 |
| Mesgana Property Services Ltd | Hospitality | 2025 |
| Messages of Herts Limited | Wholesale & retail | 2003 |
| Metal Roofing Recruitment Company Limited | Administrative & support | 2005 |
| Metra Non-Ferrous Metals Limited | Wholesale & retail | 1973 |
| MFB Osteopathy Limited | Health & social care | 2025 |
| MGD Archive Limited | Transport & logistics | 2009 |
| MGS Trans Limited | Transport & logistics | 2019 |
| Mgs-Stana Trans Ltd | Transport & logistics | 2019 |
| MGT Miroslaw Gebalik Transport Ltd | Transport & logistics | 2014 |
| MHH Proconstruct Ltd | Construction | 2017 |
| Miafreshorganics Ltd | Wholesale & retail | 2023 |
| Michael Spires Limited | Construction | 2017 |
| Michal Levin Ltd | Administrative & support | 2015 |