| Marchetti Stone Limited | Manufacturing | 2007 |
| Marcon Property Ltd | Real estate | 2021 |
| Marcus Coutts Ltd | Construction | 2026 |
| Marfam Holdings Ltd | Real estate | 2018 |
| Margots Limited | Hospitality | 2026 |
| Marllo Fire Ltd | Professional & scientific | 2023 |
| Marllo Ltd | Professional & scientific | 2013 |
| Marllo Medical Ltd | Health & social care | 2015 |
| Marney Construction Limited | Other services | 2008 |
| Marney Holdings Limited | Financial services | 2019 |
| Marney Plant Hire Limited | Administrative & support | 2015 |
| Marney Services Limited | Other services | 2022 |
| Marsdun Limited | Administrative & support | 2017 |
| Martian Sunrise Limited | Wholesale & retail | 2016 |
| Martillo Limited | Real estate | 2014 |
| Mascioni UK Limited | Wholesale & retail | 2020 |
| Maship Property Limited | Real estate | 2020 |
| Maske Strategy Software and Solutions Ltd | Information & communication | 2014 |
| Mason & ST John Ltd | Administrative & support | 2012 |
| Masters of MX Limited | Wholesale & retail | 2018 |
| Masters of Sports Limited | Wholesale & retail | 2017 |
| Mastro Ltd. | Other services | 2000 |
| Matfreale Limited | Other services | 2020 |
| Mather House Guest House Ltd | Hospitality | 2017 |
| Mathews Serjeant Architects Limited | Professional & scientific | 1999 |
| Matt's Solar Sales Limited | Wholesale & retail | 2016 |
| Mattacks Engineering & Design Limited | Professional & scientific | 1997 |
| Mavens Health Limited | Health & social care | 2017 |
| Maviswood Limited | Hospitality | 2002 |
| MAX Gray Security Ltd | Administrative & support | 2019 |
| MAX Hall Properties Ltd | Real estate | 2025 |
| MAX Motors (Southchurch) Limited | Real estate | 1946 |
| MAX Room Limited | Construction | 2016 |
| Maybury Properties Ltd | Real estate | 2024 |
| Mayflower Court Canvey Island Limited | Households | 2007 |
| Mayflower Ltd | Information & communication | 1999 |
| Mazlow Limited | Professional & scientific | 2015 |
| MB Fire Risk Limited | Professional & scientific | 2017 |
| Mbtmsc Limited | Real estate | 2023 |
| Mccarthy Plant Ltd | Other services | 2017 |
| MCM Property Developers Limited | Construction | 2017 |
| Mcmillan Construction Limited | Construction | 2023 |
| MCS AID Ltd | Information & communication | 2025 |
| Meadow Highlight Limited | Administrative & support | 2019 |
| Medic Footprints Ltd | Other services | 2014 |
| Medinspix Global Ltd | Health & social care | 2023 |
| Medira Limited | Wholesale & retail | 2008 |
| Meeracles UK Limited | Professional & scientific | 2010 |
| Mega Plumbing & Heating Services Limited | Construction | 2012 |
| Megannelly Catering Ltd | Manufacturing | 2023 |
| Menopause Training Ltd | Arts & recreation | 2025 |
| Mentality Mens Club C.I.C. | Health & social care | 2025 |
| Men’S Hair Rayleigh Ltd | Other services | 2025 |
| Merchant Connect Incorporations Limited | Administrative & support | 2017 |
| Merchant's of Spice Limited | Hospitality | 2016 |
| Merlin Circuit Technology Ltd. | Manufacturing | 1992 |
| Merlin Flex Limited | Manufacturing | 1996 |
| Merlin PCB Group Ltd | Professional & scientific | 1999 |
| Merlin Stevenage Limited | Manufacturing | 2010 |
| Mervad Electrical Ltd | Construction | 2012 |
| Metalsmith Steel Fabrications Limited | Construction | 2009 |
| Metatwin Limited | Other services | 2025 |
| MF Ventilation & Fans Limited | Construction | 2021 |
| MFK Trading Ltd | Wholesale & retail | 2026 |
| MFS Consulting Ltd | Administrative & support | 2025 |
| MGH Autocare Ltd | Wholesale & retail | 2025 |
| MGL Film & TV Ltd | Transport & logistics | 2025 |
| MHA Multi LAY Utilities Ltd | Construction | 2026 |
| MIA Pollock Ltd | Information & communication | 2025 |
| Michael HOY Ltd | Professional & scientific | 2024 |
| Michael Wigington Engineering Ltd | Professional & scientific | 2024 |
| Midas Accountancy Services Limited | Professional & scientific | 2024 |
| Mildmay Estates Limited | Real estate | 2007 |
| Miles Malone Limited | Manufacturing | 2019 |
| Mill Homes Limited | Construction | 1986 |
| Miller Advisory Ltd | Professional & scientific | 2024 |
| Miller Commercial Consulting Limited | Professional & scientific | 2013 |
| Millington Decor Limited | Construction | 2007 |
| Millmo Glazing Limited | Construction | 2020 |
| Mino Architects Limited | Professional & scientific | 2010 |
| Mirage Glass Design Limited | Construction | 2001 |
| Mirimar Limited | Information & communication | 2004 |
| Mispronounced Ltd | Professional & scientific | 2025 |
| Mission Element Limited | Professional & scientific | 2015 |
| Mitchell Property Group Ltd | Real estate | 2019 |
| Mithril Developments Limited | Construction | 2024 |
| MJH Essex Building Limited | Manufacturing | 2025 |
| MJS Training Solutions Ltd | Construction | 2018 |
| Mktwo Enterprises Limited | Manufacturing | 2021 |
| MM Motorcars Limited | Wholesale & retail | 2020 |
| MM Tyres Ltd | Wholesale & retail | 2023 |
| MMV Trans Limited | Transport & logistics | 2017 |
| MNP Property Ltd | Real estate | 2018 |
| MO & ELI Ltd | Real estate | 2026 |
| Mobile Barbers (Essex) Ltd | Other services | 2026 |
| Mobile Clutch Repair Ltd | Wholesale & retail | 2026 |
| Mobile Technical Staff Ltd | Administrative & support | 2001 |
| Mobilink South East Ltd | Other services | 2024 |
| Modern Super Coaches Limited | Real estate | 1930 |
| Modhwad Consultancy Ltd | Information & communication | 2009 |