| Mantrix Solutions Ltd | Information & communication | 2009 |
| Marco Driving Ltd | Transport & logistics | 2017 |
| Marford Group Ltd | Construction | 2025 |
| Margyver Property Development & Design Limited | Real estate | 2013 |
| Marilise DE Villiers Basson Consulting Ltd | Professional & scientific | 2017 |
| Marint (Offshore Services) Limited | Transport & logistics | 1987 |
| Marint OS Management Limited | Financial services | 2012 |
| Marint Properties Limited | Real estate | 2012 |
| Marint Property Management Limited | Financial services | 2012 |
| Mark Barwick Consulting Limited | Information & communication | 2015 |
| Marston Medical Consulting Ltd | Public administration | 2026 |
| Martin P Mulryan & Associates Limited | Professional & scientific | 2001 |
| Marvel Facilities Management Ltd | Administrative & support | 2013 |
| Mary Waring Associates Ltd | Professional & scientific | 2003 |
| Matthew Elliott Bespoke Ltd | Wholesale & retail | 2025 |
| Mawu Films Ltd | Wholesale & retail | 2021 |
| Maxilion Ltd | Construction | 2010 |
| Maxim Legal Services Ltd | Professional & scientific | 2015 |
| Maximilian Bespoke Carpentry and Joinery Ltd | Construction | 2017 |
| MAY Day Consultancy and Training Limited | Professional & scientific | 2024 |
| MAY London Ltd | Professional & scientific | 2012 |
| Mayfield Associates Limited | Real estate | 2006 |
| Mayford Innovation Limited | Professional & scientific | 2020 |
| MD & SON Limited | Other services | 2018 |
| MD Inns Ltd | Hospitality | 2025 |
| MD Learning Support Ltd | Education | 2025 |
| Mdf@Services Ltd | Other services | 2018 |
| Mdrc Consulting Ltd | Financial services | 2023 |
| Meadowbrook Developments Limited | Administrative & support | 2005 |
| Mealwiz Limited | Hospitality | 2016 |
| Meany-Bo-Beany Limited | Manufacturing | 2016 |
| Mehar MM Traders Ltd | Transport & logistics | 2022 |
| Melbourne Grove Limited | Real estate | 2020 |
| Melcro Ltd | Professional & scientific | 2009 |
| Melody MIX Media Ltd | Information & communication | 2024 |
| Memi Group Limited | Financial services | 2019 |
| Mercer Keeble Limited | Professional & scientific | 2010 |
| Metafós Ltd | Information & communication | 2012 |
| Metametrics Limited | Professional & scientific | 2005 |
| Metropolitan Financial Planning Limited | Professional & scientific | 1992 |
| Mgillett Consulting Limited | Public administration | 2014 |
| MH Legal Resourcing Ltd | Administrative & support | 2025 |
| MHB Projects Limited | Professional & scientific | 2016 |
| Mike Dixon Enterprises Ltd | Wholesale & retail | 2024 |
| Mike Solinger Limited | Administrative & support | 2006 |
| Mikee LOU SHI Limited | Financial services | 2018 |
| Mikk Studio Limited | Administrative & support | 2024 |
| Millcroft Construction Services Limited | Construction | 2020 |
| Millcroft Holdings Limited | Financial services | 2019 |
| Millcroft Services P.L.C. | Construction | 1972 |
| MIM Consultant Ltd | Health & social care | 2026 |
| Mindset Plus Limited | Health & social care | 2015 |
| Minerva Pharmaceutical Consulting Limited | Other services | 2001 |
| MINT.345 Ltd | Professional & scientific | 2016 |
| MIR Consulting Ltd | Information & communication | 2024 |
| MJA Tech Ltd | Information & communication | 2026 |
| MJK Advisory Limited | Professional & scientific | 2024 |
| MJM Assets Limited | Construction | 1962 |
| MLC Consulting Limited | Professional & scientific | 2016 |
| MLO Properties Ltd | Real estate | 2020 |
| Mobile Concepts Ltd | Information & communication | 2007 |
| Moliere West END Ltd | Arts & recreation | 2019 |
| Molloy Creative Ltd | Professional & scientific | 2015 |
| Mondo Technical Services Ltd | Information & communication | 2022 |
| Montemares Investments Limited | Real estate | 2016 |
| Moomi Ltd | Real estate | 2023 |
| Moonlit Tipis Ltd | Other services | 2022 |
| Moral Homes Ltd | Real estate | 2017 |
| Morden Living Ltd | Wholesale & retail | 2025 |
| Morph Design Studio Ltd | Professional & scientific | 2020 |
| Morton PR (UK) Limited | Information & communication | 2009 |
| Moss Data Strategy Ltd | Professional & scientific | 2020 |
| MSE Medical UK Ltd | Wholesale & retail | 2020 |
| MSJ Associates Limited | Administrative & support | 2009 |
| MSJ Design Limited | Administrative & support | 2013 |
| MSJ Studios Limited | Administrative & support | 2020 |
| MST West Ltd | Construction | 2011 |
| Mstar Consulting Ltd | Information & communication | 2024 |
| Mudroch Ltd | Professional & scientific | 2010 |
| Muffin Worship Ltd | Information & communication | 2024 |
| Mumme Mojo Limited | Wholesale & retail | 2019 |
| Munchkins Soft Play Cafe Ltd | Hospitality | 2022 |
| Musicincite Ltd | Information & communication | 2013 |
| Musters Court Limited | Real estate | 1957 |
| MW & WL Company Ltd | Real estate | 2025 |
| My Alchemy Ltd | Health & social care | 2025 |
| My Passion Boutique Ltd | Wholesale & retail | 2025 |
| Myse&Vast Group Ltd | Administrative & support | 2019 |
| Nadine Van Biljon Photography Limited | Arts & recreation | 2013 |
| Ncwts Limited | Information & communication | 2026 |
| Neatabooks Limited | Professional & scientific | 2024 |
| Nelson Derry Consulting Limited | Professional & scientific | 2024 |
| Nest Property Consultants Ltd | Construction | 2019 |
| Netpitts Limited | Information & communication | 2024 |
| Next Page Consultancy Ltd | Professional & scientific | 2020 |
| NIC Harry London Ltd | Administrative & support | 2016 |
| Nichol Properties Ltd | Real estate | 2026 |
| Nicki Young Consulting Ltd | Extraterritorial | 2017 |
| NJL - Solutions Limited | Professional & scientific | 2011 |
| NK Global Ltd | Administrative & support | 2013 |