| Maple Road Residents Association Limited | Households | 1980 |
| MAQ Logistics Ltd | Transport & logistics | 2024 |
| Marantony Ltd | Information & communication | 2026 |
| Marcas Asset Management Limited | Professional & scientific | 2019 |
| Marchmont Gate Ltd | Energy | 2011 |
| Marian Services Limited | Construction | 2015 |
| Marina Spice Lounge Ltd | Hospitality | 2010 |
| Marinade Digital Ltd | Professional & scientific | 2025 |
| Marion Wardlaw Consulting Services Ltd | Professional & scientific | 2024 |
| Mark Anthony Bywater Ltd | Other services | 2024 |
| Markate Ltd | Wholesale & retail | 2026 |
| Markwaterfield.Com Limited | Education | 2005 |
| Marleyroofingandbuilding Ltd | Construction | 2024 |
| Marlowes Grilled Limited | Hospitality | 2025 |
| Marlowes Holdings Limited | Real estate | 2021 |
| Marquess Point Property Management Limited | Households | 2005 |
| Mars Rigging Ltd | Construction | 2025 |
| Marsh Precision Plastering Ltd | Construction | 2019 |
| Marshall Bathrooms Ltd | Construction | 2015 |
| Marshment Ltd | Information & communication | 2018 |
| Marta Medical Service Ltd | Transport & logistics | 2025 |
| Martin M Limited | Construction | 2015 |
| Martin Mcleod Design Drafting Limited | Mining & quarrying | 2007 |
| Martin-Brower Scicoe United Kingdom, Ltd | Extraterritorial | 2012 |
| Martin-Brower UK Ltd | Transport & logistics | 1981 |
| Martinique Management Limited | Information & communication | 2022 |
| Martlink Trading and Business Limited | Wholesale & retail | 2024 |
| Marvin's Magic Holdings Limited | Financial services | 2013 |
| Marvin's Magic Limited | Administrative & support | 1999 |
| Marwood 252 Limited | Professional & scientific | 2012 |
| Masai Cultural Arts | Arts & recreation | 2011 |
| Masai Cultural Performance Arts Ltd | Arts & recreation | 2011 |
| Masco Doors Ltd | Construction | 2024 |
| Masco Facilities Management Limited | Construction | 2020 |
| Mascoprint Developments Limited | Manufacturing | 1972 |
| Mascoprint Holdings Ltd | Financial services | 2025 |
| Maskell Enterprise Solution Services Ltd | Information & communication | 2013 |
| Masom Associates Ltd | Information & communication | 2018 |
| Mass IT Consultancy Services Limited | Information & communication | 2004 |
| Master Marble Ltd | Construction | 2017 |
| Masterpieces by MAI Ltd | Wholesale & retail | 2025 |
| Mastone Ltd | Construction | 2015 |
| Masum Spice Limited | Hospitality | 2025 |
| MAT LUC Ltd | Construction | 2019 |
| MAT. Spedition Ltd | Transport & logistics | 2024 |
| Matchbox Design Limited | Professional & scientific | 2011 |
| Matchbox Experience Ltd | Professional & scientific | 2026 |
| Mathtastic Ltd | Administrative & support | 2016 |
| Matthew Fowles Productions Ltd | Information & communication | 2016 |
| Matty Walsh Rigging Ltd | Information & communication | 2019 |
| Matuta Consultancy Group Ltd | Professional & scientific | 2015 |
| MAV Pro Limited | Manufacturing | 2015 |
| MAV Signs Ltd | Construction | 2020 |
| Maverick Private Holdings Ltd | Financial services | 2026 |
| Maverix UK Trading Ltd | Transport & logistics | 2024 |
| Mavis Transport Limited | Transport & logistics | 2024 |
| Maxcatam Properties Ltd | Real estate | 2022 |
| Maxhldg Limited | Financial services | 2023 |
| Maximise Property Investments Limited | Real estate | 2017 |
| Maxis Retail Ltd | Wholesale & retail | 2021 |
| Maxvault Ltd | Wholesale & retail | 2025 |
| Maxwell Andrew Developments Ltd | Construction | 2020 |
| Maxwell Mortgages Ltd | Administrative & support | 2019 |
| Maxwell Properties Ltd | Real estate | 2020 |
| Maybank Properties Limited | Real estate | 2015 |
| Mayfair Estate Agents Limited | Real estate | 2015 |
| Mayfaire Properties Limited | Real estate | 2024 |
| Mayflower Ceiling Services Limited | Construction | 2003 |
| Mayflower Refurbishment Limited | Construction | 2019 |
| Mayhew Education Ltd | Education | 2023 |
| Maylands Car Sales Limited | Wholesale & retail | 2014 |
| Maylands HCW Ltd | Wholesale & retail | 2022 |
| Maylands Property Holdings Limited | Real estate | 2017 |
| Maynecol Services Limited | Construction | 1984 |
| Maytree Limited | Construction | 2002 |
| MAZ Glazing Ltd | Construction | 2023 |
| Maze Utilities Ltd | Construction | 2021 |
| Maziak Compressor Services Limited | Manufacturing | 1990 |
| Mazin ABU Sayf Ltd | Information & communication | 2017 |
| MB Healthcare Solutions Limited | Administrative & support | 2023 |
| MB Store Ltd | Wholesale & retail | 2014 |
| Mbantu Ltd | Administrative & support | 2025 |
| Mbiziz Ltd | Wholesale & retail | 2019 |
| MBM Concrete Limited | Manufacturing | 2020 |
| MBM Groundworks Limited | Construction | 2016 |
| MBM Properties London Limited | Real estate | 2019 |
| Mbome Limited | Public administration | 2025 |
| MC Delights Ltd | Hospitality | 2025 |
| MC Kenna Property Ltd | Financial services | 2017 |
| MC Rental Properties Ltd | Real estate | 2025 |
| MCB Admin Services Ltd | Extraterritorial | 2018 |
| Mcbirnie Ltd | Professional & scientific | 2024 |
| Mccollin Consulting Ltd | Information & communication | 2019 |
| Mcewan Manufacturing and Technical Solutions Ltd | Professional & scientific | 2019 |
| Mcfagin Holdings Ltd | Administrative & support | 2016 |
| Mcgill Homes Limited | Construction | 1993 |
| Mckenzie Design & Build Ltd | Construction | 2011 |
| Mclaren British Construction Limited | Construction | 2018 |
| Mclecare Ltd | Health & social care | 2023 |
| Mclupa Ltd | Transport & logistics | 2019 |