| Mercury Forecourts Ltd | Professional & scientific | 2008 |
| Methodraise Limited | Wholesale & retail | 1991 |
| MF Management Solutions Limited | Professional & scientific | 2000 |
| MFG EV Power Limited | Financial services | 2021 |
| Mglovin Ltd | Wholesale & retail | 2018 |
| MGS Trades Limited | Construction | 2006 |
| MI7 Music Limited | Information & communication | 2005 |
| Michael Anthony (Hemel Hempstead) Limited | Real estate | 1997 |
| Microtec Solutions Limited | Professional & scientific | 2001 |
| MID Herts Executive Relocation Ltd | Real estate | 2003 |
| Midas Group Consultancy Ltd | Professional & scientific | 2021 |
| Middeys Saltgrass (Cockfosters) Ltd | Hospitality | 2018 |
| Mike Breese Limited | Administrative & support | 2003 |
| Mike Goddard Limited | Wholesale & retail | 2002 |
| Mila Kebab Ltd | Hospitality | 2022 |
| Milk & Black Ltd | Wholesale & retail | 2025 |
| Millennium Solutions (Herts) Ltd | Construction | 2006 |
| Milliellen Limited | Real estate | 2003 |
| Milltech Solutions Limited | Information & communication | 1998 |
| Millwood Medical Limited | Professional & scientific | 1995 |
| Miltonica Garb Private Limited | Wholesale & retail | 2023 |
| Mimi@Nails Ltd | Real estate | 2026 |
| Mimosa Developments Limited | Construction | 1987 |
| Mind Body Wellness Limited | Health & social care | 2019 |
| Mind Management Consultancy Ltd | Professional & scientific | 2008 |
| Mine of Information Limited | Information & communication | 1977 |
| Ministry of I.T. Ltd | Administrative & support | 2003 |
| Minshull Architectural Design Ltd | Professional & scientific | 2000 |
| Mishpacha (E9) Limited | Real estate | 2025 |
| Mission Impossible Hospitality Ltd | Wholesale & retail | 2000 |
| Mister MOW Ltd | Other services | 2025 |
| Mitsubishi Electric Finance Europe PLC | Financial services | 1990 |
| Mixed Images Limited | Professional & scientific | 1985 |
| MJG Property Maintenance Limited | Construction | 1997 |
| MJL Advertising Limited | Professional & scientific | 2002 |
| Mjwr Property Ltd | Real estate | 2022 |
| MK Auto Hub Ltd | Wholesale & retail | 2025 |
| MK Healthcare Communications Ltd | Professional & scientific | 2015 |
| MKF Management Services Limited | Professional & scientific | 2003 |
| MLC Advisors Ltd | Professional & scientific | 2025 |
| MMI Solutions Limited | Information & communication | 2018 |
| MN HLD Ltd | Information & communication | 2020 |
| MNT Estates Ltd | Real estate | 2020 |
| Mobile Stationery & Printing Centre Limited | Manufacturing | 1998 |
| Mobile Xpertz Limited | Wholesale & retail | 2021 |
| Modd Architects Ltd | Professional & scientific | 2024 |
| Mode Electronics Limited | Extraterritorial | 1987 |
| Mode Lighting Limited | Manufacturing | 1987 |
| Modgraph Consultants Limited | Information & communication | 1993 |
| Monarchs View Management Company Limited | Households | 2026 |
| Money Tree Investment & Properties Limited | Real estate | 2024 |
| Moor Park Estates Limited | Real estate | 2004 |
| Moor Park Golf Club Limited | Arts & recreation | 1937 |
| Moorgate Services Limited | Professional & scientific | 1958 |
| Morannedd Limited | Professional & scientific | 2003 |
| Morganism Limited | Information & communication | 2000 |
| Morrisroe Limited | Construction | 1977 |
| Mortgage Solutions (CRE) Limited | Financial services | 2006 |
| Mortoo Homes Ltd | Real estate | 2015 |
| Motivelectronics Limited | Manufacturing | 1998 |
| Motor Fuel (NO.1) Limited | Extraterritorial | 2008 |
| Motor Fuel (NO.2) Limited | Extraterritorial | 2015 |
| Motor Fuel (NO.3) Limited | Wholesale & retail | 2011 |
| Motor Fuel (NO.4) Limited | Real estate | 2016 |
| Motor Fuel (NO.5) Limited | Wholesale & retail | 2007 |
| Motor Fuel (NO.6) Limited | Wholesale & retail | 2010 |
| Motor Fuel Group Limited | Extraterritorial | 2007 |
| Motor Fuel Limited | Wholesale & retail | 2004 |
| Motorhome and Caravan Habitation Service and Repair Ltd | Manufacturing | 2020 |
| Motorsport World Limited | Arts & recreation | 2002 |
| Mountway Property Company Limited | Real estate | 1987 |
| Movies Video Limited | | 1991 |
| Moyomichelle Medical Consult Limited | Real estate | 2012 |
| Mparsec Limited | Information & communication | 2020 |
| MPL Training Solutions Limited | Professional & scientific | 2004 |
| MPM Interiors Limited | Administrative & support | 1999 |
| MR Kent Construction Ltd | Construction | 2021 |
| MR Keys & Shoes Ltd | Manufacturing | 2013 |
| MR. H Enterprises Limited | Professional & scientific | 2006 |
| MRH (GB) Limited | Professional & scientific | 2007 |
| MS Diva Limited | Other services | 2016 |
| MSS Consultancy Services Limited | Information & communication | 2018 |
| Much Hadham Square Management Company Limited | Households | 1993 |
| Muddy Lane Sports Ground Ltd | Arts & recreation | 2004 |
| Mulla Properties Ltd | Real estate | 2023 |
| Mullucks Wells Ltd | Real estate | 2003 |
| Multilayer Tech Limited | Information & communication | 2013 |
| Murgatroyds Limited | Real estate | 1998 |
| Musley Grove Management Company Limited | Households | 1987 |
| MW East Anglia Ltd | Real estate | 2003 |
| My GRC Partner Ltd | Professional & scientific | 2024 |
| Myivista Ltd | Real estate | 2024 |
| Mymoni Limited | Financial services | 2016 |
| Myriad Security Limited | Administrative & support | 2005 |
| N a Marlow Dairy Produce Limited | Administrative & support | 2005 |
| N Ferguson Consulting Services Limited | Professional & scientific | 2020 |
| N W London Property Maintenance Limited | Construction | 2025 |
| N.C. Engineering Limited | Extraterritorial | 2007 |
| N.E.M. Co. Limited | Manufacturing | 1983 |
| N.J. Akers & Co Limited | Information & communication | 2004 |