| Matthews-Cowan Associates Limited | Professional & scientific | 2022 |
| Mayfair Psychiatrists Limited | Health & social care | 2020 |
| Mayfairfowler Ltd. | Other services | 2011 |
| Mayrose Consulting Limited | Professional & scientific | 2022 |
| Mcdonogh, Small and Associates Ltd. | Health & social care | 2008 |
| Mciver Consulting Limited | Professional & scientific | 2025 |
| Mckay Cleaning Services Limited | Other services | 2010 |
| Mckenzie's IT Services Limited | Professional & scientific | 1992 |
| Mckenzie-Smart Holdings Limited | Financial services | 2011 |
| Mckenzie-Smart Nominees Limited | Professional & scientific | 2013 |
| Mckenzies Accountancy Limited | Professional & scientific | 1967 |
| Mckenzies ATS Limited | Professional & scientific | 2018 |
| Mckenzies Group Ltd | Financial services | 2022 |
| Mckg Hold Co Ltd | Financial services | 2023 |
| Mckg Ltd | Professional & scientific | 2022 |
| Mclaren Investments Limited | Extraterritorial | 2018 |
| Mcnally Engineering Management Limited | Professional & scientific | 2005 |
| MDB Therapy Ltd | Professional & scientific | 2024 |
| MDH Business Solutions Limited | Professional & scientific | 2008 |
| Mediavault Digital Ltd | Information & communication | 2026 |
| Medical Logic Ltd | Professional & scientific | 2013 |
| Mela-Nu Consulting Limited | Administrative & support | 2023 |
| Melville Advisory Ltd | Administrative & support | 2023 |
| Mema Capital Limited | Professional & scientific | 2020 |
| Menaphar Property Management Limited | Construction | 2023 |
| Meredith Corporation Limited | Administrative & support | 2022 |
| Meridian Treatment Centre Ltd | Health & social care | 2020 |
| Meridian VR Limited | Professional & scientific | 2020 |
| Merlewood Property Solutions (Middlesbrough) Limited | Real estate | 2023 |
| Merlewood Property Solutions Limited | Real estate | 2017 |
| Merlin Gym Limited | Arts & recreation | 2025 |
| Merlin Property (Kingston) Ltd | Real estate | 2019 |
| Merritt and Melrose Limited | Professional & scientific | 2026 |
| Mesher Consulting Limited | Professional & scientific | 2023 |
| Metis Strategy Group Ltd | Professional & scientific | 2025 |
| Metro Security (UK) Holdings Limited | Financial services | 2026 |
| Mettle & Bond Care Ltd. | Health & social care | 2016 |
| Meyricke Family Holdings Limited Liability Partnership | | 2021 |
| Meyricke Holdings Limited | Financial services | 2021 |
| MHC Legal Limited | Administrative & support | 2015 |
| MID Kent Breakers Limited | Water & waste | 2008 |
| MID Kent Metals Recycling Limited | Water & waste | 2002 |
| Midas Global Holdings Limited | Real estate | 2026 |
| Mike Bliss Architecture Limited | Professional & scientific | 2013 |
| Milamei Ltd | Wholesale & retail | 2019 |
| Militao Carpentry Ltd | Construction | 2021 |
| Minerva Nursing Ltd | Health & social care | 2013 |
| Mitzi Property Ltd | Real estate | 2021 |
| MJ & M Consulting Limited | Professional & scientific | 2014 |
| Mldigitech Ltd | Administrative & support | 2016 |
| MLG Music Ltd | Information & communication | 2022 |
| Mndw Property Ltd | Construction | 2025 |
| Moat Farm Properties Limited | Real estate | 2013 |
| Moaty & Crow Ltd | Manufacturing | 2021 |
| Monwell Limited | Wholesale & retail | 2016 |
| Moonberry London Limited | Wholesale & retail | 2021 |
| Moor Foliage Limited | Agriculture & fishing | 2026 |
| Moorgate Accountancy Ltd | Professional & scientific | 2012 |
| Moorgate Accountancy Services Ltd | Professional & scientific | 2017 |
| Moorgate R&D Tax Claims Ltd | Professional & scientific | 2022 |
| Moorhouse Recruitment Limited | Administrative & support | 2021 |
| Morgan Consulting (Surrey) Limited | Construction | 2003 |
| Morgan Homes (Surrey) Limited | Real estate | 2005 |
| Morgan Owen Developments Limited | Construction | 2004 |
| Morgan Stark Events Ltd | Arts & recreation | 2015 |
| Morton-Smith RPC Ltd | Professional & scientific | 2023 |
| Moss James Limited | Professional & scientific | 2001 |
| Mount View Consulting Limited | Professional & scientific | 2020 |
| Mowling Limited | Real estate | 1962 |
| MR T Productions Limited | Professional & scientific | 2017 |
| MRW Group Limited | Professional & scientific | 2022 |
| MS Digital Marketing Limited | Professional & scientific | 2023 |
| MSR Heating & Plumbing Limited | Administrative & support | 2010 |
| Multiplex Store Limited | Wholesale & retail | 2025 |
| Muse Global Master Fund Limited | Financial services | 2014 |
| Musteco Ltd | Transport & logistics | 2022 |
| MV Nails & Beauty Ltd | Other services | 2017 |
| Mvine Limited | Information & communication | 2004 |
| MW Contracts (Roofing) Limited | Construction | 1989 |
| Mwab Limited | Real estate | 2018 |
| My Club Europe PLC | Wholesale & retail | 2019 |
| My Club Funding Limited | Arts & recreation | 2019 |
| My Club Global Limited | Wholesale & retail | 2024 |
| My Club Group Limited | Financial services | 2017 |
| My Club Limited | Information & communication | 2018 |
| My Club Lottery Limited | Arts & recreation | 2019 |
| My Club Lotto Limited | Arts & recreation | 2019 |
| My Club Patents Limited | Professional & scientific | 2022 |
| My Club United States Limited | Information & communication | 2019 |
| My Club World Limited | Information & communication | 2018 |
| My Teamwear Limited | Information & communication | 2024 |
| Mycodiie Ltd | Information & communication | 2026 |
| Mylton Consultancy Ltd | Administrative & support | 2017 |
| Mystic Capital Advisors Limited | Professional & scientific | 2014 |
| NA Events Ltd | Arts & recreation | 2019 |
| Naomi Gayler Limited | Information & communication | 2016 |
| National AI Matching Service Limited | Information & communication | 2025 |
| National Meats Limited | Transport & logistics | 1999 |
| Nationwide Roofing Products Ltd | Construction | 2020 |
| Native Natural Wines Ltd | Wholesale & retail | 2025 |