| MM Security Limited | Administrative & support | 2022 |
| MM Surrey Construction Limited | Construction | 2021 |
| MM Tech Consulting Ltd | Information & communication | 2026 |
| MM2 Global Limited | Professional & scientific | 2020 |
| Mmaak Consultancy Ltd | Professional & scientific | 2025 |
| Mmarrs Developments Limited | Real estate | 2010 |
| Mmarrs Investments Ltd | Financial services | 2015 |
| Mmgeraghty Consulting Limited | Information & communication | 2005 |
| MMQ Consultancy Ltd | Transport & logistics | 2023 |
| Mnag Fleet Solutions Ltd | Wholesale & retail | 2026 |
| MNL Logistics Ltd | Transport & logistics | 2019 |
| MNR Holdings Ltd | Households | 2021 |
| MO Care Prestige Limited | Health & social care | 2025 |
| Mo'Araola Classics Ltd | Transport & logistics | 2026 |
| Moab Resolutions Limited | Professional & scientific | 2016 |
| Moat House Property Management Limited | Administrative & support | 1996 |
| Moatenden Investments Limited | Real estate | 2015 |
| Moatenden Property Investment LLP | | 2015 |
| Mobicell Blue Ocean Wireless Ltd. | Information & communication | 2011 |
| Mobile Auto Repairs (Laleham) Limited | Wholesale & retail | 2011 |
| Mobile Biitz Ltd | Other services | 2019 |
| Mobile Catering Ashford Ltd | Hospitality | 2025 |
| Mobile Mechanic Group Ltd | Wholesale & retail | 2026 |
| Mobile Repair 'N' Paint Ltd | Wholesale & retail | 2018 |
| Mobmodz Limited | Wholesale & retail | 2018 |
| Mockford and Hunt Limited | Real estate | 2020 |
| Moda Frankfurt Ltd | Other services | 2019 |
| Moderation Public House Ltd | Hospitality | 2010 |
| Modern Structure Building Contractors Ltd | Construction | 2021 |
| Modernus Living Ltd | Construction | 2020 |
| Modrofit Ltd | Construction | 2015 |
| Modus Airtech (Thermodynamics) Limited | Administrative & support | 1985 |
| Modus Consultancy Ltd | Public administration | 2018 |
| Modus Film Productions Limited | Information & communication | 2014 |
| Modvic Group of Companies Ltd | Information & communication | 2011 |
| Moid Kitchens Limited | Hospitality | 2025 |
| Moid Motors Ltd | Wholesale & retail | 2025 |
| Molesey Property Ltd | Real estate | 2008 |
| Molloy Advisory Limited | Professional & scientific | 2017 |
| Moments Made Clean Ltd | Manufacturing | 2025 |
| Momentum Accounting Ltd | Professional & scientific | 2022 |
| Momentum Building Co Ltd | Construction | 2023 |
| Momentum CBS Ltd | Real estate | 2021 |
| Momoh Olajumoke Deborah Limited | Health & social care | 2023 |
| Mona-Madhav Company Limited | Health & social care | 2017 |
| Mondee Limited | Other services | 2010 |
| Money Mapping Financial Services Ltd | Professional & scientific | 2025 |
| Money Mindful Group Ltd | Information & communication | 2022 |
| Money Sense IFA Ltd | Financial services | 2022 |
| Money U Ltd | Professional & scientific | 2025 |
| Moneytree Network Ltd | Information & communication | 2025 |
| Monkey Fuse Ltd | Information & communication | 2025 |
| Monks Facilities Management Limited | Construction | 2020 |
| Monopoly Homes Limited | Professional & scientific | 2007 |
| Montague London Limited | Construction | 2018 |
| Montra Invicta Limited | Real estate | 2017 |
| Montrose Landscape Gardening Ltd | Administrative & support | 2022 |
| Monviso Property Ltd | Real estate | 2021 |
| Moodl Ltd | Administrative & support | 2019 |
| Moody Care Ltd | Health & social care | 2018 |
| Mooji Foundation Ltd | Education | 2009 |
| Mooji Media Ltd | Education | 2009 |
| Moon Bear Publishing Ltd | Information & communication | 2024 |
| Moon Investments Ltd | Real estate | 2021 |
| Moonbridge Air and Project Services Limited | Transport & logistics | 1986 |
| Moore Rail Limited | Construction | 2015 |
| Moore Storage Ltd | Construction | 2003 |
| Moorgate Asset Management Ltd | Professional & scientific | 2016 |
| Moorhouse Property Management Ltd | Real estate | 2018 |
| Mootinvest Limited | Construction | 2006 |
| Moovi Group Limited | Information & communication | 2026 |
| Mopane Tree Ltd | Wholesale & retail | 2015 |
| More Than Cancer Limited | Financial services | 2023 |
| More Than Diabetes Limited | Financial services | 2022 |
| More Than Money Limited | Financial services | 2018 |
| More Than Property (SE) Limited | Real estate | 2021 |
| Morecare Services International Ltd | Health & social care | 2026 |
| Moreton George Limited | Professional & scientific | 2017 |
| Morghew Park Estate Limited | Agriculture & fishing | 2001 |
| Mori Investments Ltd | Financial services | 2025 |
| Mori Property Ltd | Real estate | 2026 |
| Morlais Ridge Fields Limited | Financial services | 2024 |
| Morley Bespoke Ltd | Manufacturing | 2022 |
| Morphy Builds Ltd | Real estate | 2025 |
| Morris Dobbs Property Limited | Real estate | 2017 |
| Morris Merryweather Limited | Real estate | 1967 |
| Morrison Holdings Ltd | Real estate | 2025 |
| Morse Systems Engineering Ltd | Manufacturing | 2002 |
| Morsson Pyper Limited | Professional & scientific | 2019 |
| Mortgage AI Toolkit Ltd | Information & communication | 2016 |
| Mortgagx Ltd | Information & communication | 2024 |
| Mortimer Street LLP | | 2009 |
| Morviqa Technologies Ltd | Information & communication | 2026 |
| Mosaic Apartments RTM Company Limited | Households | 2026 |
| Moseley Property Investments Ltd | Construction | 2021 |
| Moses Equity Group Ltd | Financial services | 2025 |
| Moss Fabrications Ltd | Manufacturing | 2009 |
| Moss Landscapes Limited | Administrative & support | 2006 |
| Moss Quaye Health Ltd | Health & social care | 2019 |
| Motion Health & Fitness Ltd | Health & social care | 2023 |