| M&N Electrical & General Maintenance Ltd | Manufacturing | 2020 |
| M.A.P Property Development Limited | Real estate | 2017 |
| M.D. Tank Services Ltd | Other services | 2023 |
| M.D.C Investments Ltd | Real estate | 2018 |
| M.J. Performing Arts Ltd | Education | 2023 |
| M.T.Porter Electrical Ltd | Construction | 2021 |
| MA Electrical Wholesale Ltd | Wholesale & retail | 1997 |
| MAB Plus 3 Consulting Ltd | Financial services | 2024 |
| MAB Property Solutions Ltd | Real estate | 2025 |
| Mabrook Advisory Ltd | Wholesale & retail | 2025 |
| MAC Education Limited | Education | 2022 |
| Mack 1 Design & Build Limited | Construction | 2018 |
| Mackie Contracts Essex Ltd | Construction | 2012 |
| Mackie Transport Limited | Transport & logistics | 2003 |
| MAD Fire & Security Consulting Limited | Professional & scientific | 2017 |
| MAD Management Limited | Administrative & support | 2002 |
| Maer Automation Limited | Construction | 2023 |
| Maer Consulting Limited | Professional & scientific | 2021 |
| Maer Engineering Limited | Professional & scientific | 2020 |
| Mage Developments Ltd | Real estate | 2025 |
| Mage Motors Ltd | Wholesale & retail | 2025 |
| Mage Services Ltd | Construction | 2022 |
| Magrath Consulting Limited | Administrative & support | 2014 |
| Maha Benfleet Ltd | Hospitality | 2024 |
| Mahsez Limited | Hospitality | 2016 |
| Mainstay Holdings Limited | Financial services | 2017 |
| Mainstay International Limited | Professional & scientific | 2020 |
| Mainstay Partners Limited | Professional & scientific | 2000 |
| Mainstream Networks Limited | Construction | 2018 |
| Majestic D&B Limited | Construction | 2020 |
| Make One Aquisitions Ltd | Other services | 2015 |
| Make One Holdings Ltd | Financial services | 2019 |
| Make One London Ltd | Construction | 2004 |
| Make One Specialist Works Ltd | Construction | 2019 |
| Make-Me-Well Ltd | Public administration | 2024 |
| Maker Consultants Ltd | Professional & scientific | 2017 |
| Makers of Fine Things Ltd | Manufacturing | 2025 |
| Making the Most Ltd | Wholesale & retail | 2022 |
| Malax Properties Ltd | Real estate | 2022 |
| Maldon Gift Company Limited | Real estate | 2012 |
| Maldon Roofing Services Ltd | Construction | 2020 |
| Malevelon Consulting Ltd | Professional & scientific | 2024 |
| Malisa Care Ltd | Health & social care | 2012 |
| Malyan Property Maintenance Limited | Construction | 2019 |
| MAM Productions Ltd | Information & communication | 2012 |
| MAN CAN DO Ltd | Construction | 2024 |
| Manage My Admin Ltd | Households | 2023 |
| Managing Solutions Ltd | Professional & scientific | 2012 |
| Mandy's Ice's Limited | Hospitality | 2009 |
| Maneo Ltd | Professional & scientific | 2010 |
| Manor Building Supplies Ltd | Extraterritorial | 2011 |
| Manor Reclaim Ltd | Wholesale & retail | 2011 |
| Manor Road Drycleaners Limited | Other services | 2021 |
| Manor Service Centre Limited | Wholesale & retail | 2021 |
| Manor Sterling Properties Ltd | Real estate | 2021 |
| Manor Timber Supplies Ltd | Extraterritorial | 2017 |
| Mans Cave Ltd | Other services | 2022 |
| Mansion Construction Limited | Construction | 2010 |
| Manson Tree Services Ltd | Administrative & support | 2025 |
| Mansons Tree Services Ltd | Administrative & support | 2023 |
| Maplebridge Properties Ltd | Real estate | 2020 |
| Maprock Ltd | Real estate | 2022 |
| Marc's Star Motors Ltd | Wholesale & retail | 2020 |
| Marchants & Co Ltd | Construction | 2013 |
| Marchants Developments Ltd | Construction | 2013 |
| Marchants Investments Ltd | Real estate | 2020 |
| Marcs Consulting Limited | Administrative & support | 2016 |
| Margot Lombaert Limited | Professional & scientific | 2015 |
| Marine Bathrooms & Kitchens of Leigh on Sea Ltd | Construction | 2012 |
| Marine Garage Services LLP | | 2008 |
| Mariners Farm (Caravan) Limited | Real estate | 2009 |
| Mariners Farm (Marine) Limited | Real estate | 2009 |
| Mark Bessell Engineering & Consultancy Limited | Mining & quarrying | 2016 |
| Mark Latter (Services) Ltd | Construction | 2013 |
| Mark Spear Limited | Financial services | 2016 |
| Mark Steel Fabrication Ltd | Manufacturing | 2021 |
| Market Footprint Limited | Information & communication | 2010 |
| Marketing & Events Solutions Ltd | Professional & scientific | 2026 |
| Marks Carpet Shop Limited | Wholesale & retail | 2010 |
| Marlan Events Ltd | Administrative & support | 2025 |
| Marlin Property Ltd | Professional & scientific | 2015 |
| Marloweville Limited | Wholesale & retail | 2024 |
| Marmik Consultancy Limited | Professional & scientific | 2025 |
| Marshall North Ltd | Wholesale & retail | 2023 |
| Martin Brothers Properties Limited | Real estate | 2017 |
| Martin Claisse Associates LLP | | 2018 |
| Martine Care Limited | Health & social care | 2012 |
| Maryam Management Limited | Real estate | 2015 |
| Maso Apps Ltd | Information & communication | 2014 |
| Mason Projects Limited | Construction | 2017 |
| Masterplan G2 Ltd | Transport & logistics | 2021 |
| Masterplan Investments Limited | Real estate | 2023 |
| Masters 4 Stone Limited | Construction | 2012 |
| Mastic Guys Limited | Construction | 2015 |
| Matchfit Strength & Conditioning Ltd | Wholesale & retail | 2012 |
| Matrix Groundwork Consultancy Ltd | Professional & scientific | 2024 |
| Matt Atkins Training and Development Ltd | Education | 2015 |
| Mattell Social Limited | Real estate | 2022 |
| Matthews Builders Rayleigh LLP | | 2015 |
| Max&Company Ltd | Other services | 2026 |