| M&S Fried Chicken Limited | Hospitality | 2011 |
| M. Morina Builders Limited | Construction | 2007 |
| M. Rutter Paving Limited | Wholesale & retail | 2004 |
| M.C. Kershaw & Co. Limited | Professional & scientific | 1985 |
| M.G. Foods (London) Limited | Hospitality | 2023 |
| M.M. Property Services (UK) Limited | Administrative & support | 2005 |
| M1 Motors LDN Limited | Wholesale & retail | 2025 |
| M16M Construction Ltd | Construction | 2023 |
| MA Revolve Ltd | Wholesale & retail | 2021 |
| Maanick Construction Ltd | Construction | 2024 |
| MAC Lifting Ltd | Construction | 2022 |
| MAC Star Limited | Hospitality | 2024 |
| Macalino Group Ltd | Wholesale & retail | 2023 |
| Mach One Investments Ltd | Real estate | 2024 |
| Machine 4 Living LLP | | 2014 |
| Macintyre Media Limited | Professional & scientific | 2021 |
| MAD Inflatable Photo Booths Ltd | Professional & scientific | 2017 |
| Made by Roxana Style Limited | Other services | 2025 |
| Madeira Grove Management Company Limited | Households | 2007 |
| Madeline Ltd | Health & social care | 2014 |
| Madflo Building and Maintainance Ltd | Construction | 2024 |
| Madina MAX Care Ltd | Health & social care | 2024 |
| Maestrox Ltd | Wholesale & retail | 2024 |
| Magasa Ltd | Construction | 2014 |
| Magictouch Services Ltd | Administrative & support | 2024 |
| Magma Solutions Limited | Education | 2021 |
| Magnetic Property Limited | Real estate | 2016 |
| Mahar Staffing Ltd | Administrative & support | 2026 |
| Maindrive Ltd | Construction | 2017 |
| Maison Aurelius Ltd | Wholesale & retail | 2025 |
| Maison Noir Limited | Hospitality | 2008 |
| Majapi Ltd | Real estate | 2023 |
| Majha Construction 02 Limited | Construction | 2024 |
| MAK & Associates Ltd | Professional & scientific | 2021 |
| Makafui Enterprise Limited | Health & social care | 2009 |
| Malley 7 Ltd | Real estate | 2022 |
| Malligai Dental Academy Limited | Education | 2024 |
| Mallor-E Park Ltd | Arts & recreation | 2025 |
| Malmesbury House (South Woodford) Management Company Limited | Households | 1977 |
| MALOR0 Ltd | Arts & recreation | 2023 |
| Malph Holdings Limited | Administrative & support | 2025 |
| Malsom Ltd | Wholesale & retail | 2020 |
| Mammoth Buildings Ltd | Extraterritorial | 2020 |
| Manalishi Servcom Ltd | Professional & scientific | 2021 |
| Mandy's Little Hearts Limited | Health & social care | 2026 |
| Manifq UK Ltd | Wholesale & retail | 2025 |
| Manobtv Ltd | Information & communication | 2024 |
| Manolo Aurilia Ltd | Information & communication | 2023 |
| Manor Bricks Ltd | Real estate | 2026 |
| Manor Holdings Essex Limited | Other services | 2019 |
| Manzan Properties Limited | Real estate | 2025 |
| Mapsf Holdings Limited | Real estate | 2025 |
| Maptec Limited | Information & communication | 2017 |
| MAR Advisory Limited | Professional & scientific | 2021 |
| MAR Care Limited | Health & social care | 2015 |
| Marais Associates Limited | Health & social care | 2016 |
| Marathon Real Estates Ltd | Real estate | 2021 |
| Marcham Properties Limited | Real estate | 2026 |
| Marco DE Belen Ltd | Professional & scientific | 2013 |
| Marcufixings Ltd | Construction | 2025 |
| Maream Limited | Real estate | 2003 |
| Marie Middleton Limited | Wholesale & retail | 2017 |
| Marimor Estates Ltd | Real estate | 2022 |
| Mariya's Collection Ltd | Wholesale & retail | 2024 |
| Mark Reed Ltd | Information & communication | 2025 |
| Market Place Premium Finance Limited | Financial services | 2017 |
| Marketing Pro Solution Limited | Wholesale & retail | 2025 |
| Marks Driving School Ltd | Administrative & support | 2016 |
| Marla Properties Ltd | Real estate | 2017 |
| Marleys Hornchurch Ltd | Hospitality | 2026 |
| Marmora Limited | Health & social care | 1999 |
| Marmovest Ltd | Construction | 2013 |
| Maroof Management Service Limited | Real estate | 2021 |
| Marshall Developments London Ltd | Construction | 2023 |
| Marshall Shopfront Limited | Construction | 2019 |
| Martin Coster Construction Ltd | Professional & scientific | 2026 |
| Martisius Ltd | Construction | 2008 |
| Maru Proprties Limited | Real estate | 2023 |
| Marvellous Hope Ltd | Professional & scientific | 2026 |
| Masino Investments Ltd | Real estate | 2025 |
| Masons Roofing Limited | Construction | 2013 |
| Masood Gynaecology Ltd | Health & social care | 2024 |
| Massless Emea Ltd. | Manufacturing | 2016 |
| Master Maintenance Properties Ltd | Real estate | 2025 |
| Masterfair Ltd | Wholesale & retail | 2014 |
| Mat&Mat Ltd | Construction | 2025 |
| Matana & Co Limited | Real estate | 2014 |
| Material Recycling Solutions UK Ltd | Professional & scientific | 2018 |
| Matlocks Limited | Other services | 2007 |
| Matrix Flooring Ltd | Construction | 2019 |
| Matthew Hart Limited | Education | 2012 |
| Mauro Marino Ltd | Professional & scientific | 2010 |
| Mava Investments Ltd | Administrative & support | 2017 |
| Mavai Modern Medical LLP | | 2018 |
| Maverick Works Limited | Information & communication | 2015 |
| Mawney Security Limited | Administrative & support | 2009 |
| Maximum Drylining Ltd | Construction | 2017 |
| Maxq UK Ltd | Wholesale & retail | 2012 |
| MAY MAN Ltd | Hospitality | 2023 |
| Maybach Consultancy Limited | Professional & scientific | 2017 |