| Mentar Ltd | Information & communication | 2025 |
| Mercurio Investment Limited | Administrative & support | 2014 |
| Mercy Support Limited | Health & social care | 2018 |
| Meridian Health and Leisure Limited | Arts & recreation | 1979 |
| Meridian Mechanical Limited | Construction | 2026 |
| Merseyside Internet Services Limited | Professional & scientific | 1995 |
| Merson Silver Ltd | Administrative & support | 2017 |
| Merson Silver Properties Ltd | Real estate | 2018 |
| Mettal Consulting Limited | Extraterritorial | 2024 |
| Mettal Design Limited | Extraterritorial | 2024 |
| Mettal Group Limited | Extraterritorial | 2024 |
| Mettal Hire Limited | Extraterritorial | 2024 |
| Mettal Infrastructure Limited | Construction | 2020 |
| Meyer Property Investment Ltd | Real estate | 2023 |
| MF01 Properties Limited | Real estate | 2024 |
| MGF Property Management Ltd | Real estate | 2013 |
| MGK Family Ltd | Construction | 2025 |
| MI - PAD Solutions Limited | Administrative & support | 2015 |
| Mi-Tec Ltd | Administrative & support | 1998 |
| MIA Property Investments Ltd | Real estate | 2019 |
| Michael Glassock Coaching Limited | Administrative & support | 2024 |
| Micheal Drew Integrated Facilities Company Limited | Administrative & support | 2026 |
| Michelle Pauli Ltd | Arts & recreation | 2009 |
| Micro Minder Limited | Information & communication | 1984 |
| MID Glamorgan Internet Services Limited | Professional & scientific | 1995 |
| Midessex Holdings Limited | Real estate | 2016 |
| Midha Holdings Limited | Professional & scientific | 2020 |
| Midori Group Limited | Real estate | 2018 |
| Mike 668 Ltd | Hospitality | 2019 |
| Mill Pharm Limited | Wholesale & retail | 2008 |
| Millady Limited | Financial services | 2021 |
| Millard House Care Ltd | Administrative & support | 2015 |
| Millfield Contracts Limited | | 1992 |
| Millmate Ltd | Financial services | 2019 |
| Mimshak Limited | Health & social care | 2020 |
| Minerva Analytics Limited | Administrative & support | 2018 |
| Minerva Smile Limited | Health & social care | 2024 |
| Mings Witham Ltd | Hospitality | 2024 |
| Mini Marvels Nursery Limited | Health & social care | 2014 |
| Minston Green Limited | Manufacturing | 2025 |
| Mintek UK Ltd | Information & communication | 2003 |
| Mirosa Ltd | Real estate | 2024 |
| Missi&Ros Limited | Health & social care | 2023 |
| Missy-Tank Limited | Construction | 2007 |
| Mitrovic Ltd | Real estate | 2025 |
| MJH Airconditioning and Refrigeration Ltd | Construction | 2022 |
| MJR Business Services Ltd | Administrative & support | 2017 |
| MK Plant Ltd | Administrative & support | 2021 |
| MKS Kitchen Installations Limited | Other services | 2011 |
| MM Global Holdings Limited | Financial services | 2025 |
| MME Landscape and Gardening Limited | Administrative & support | 2025 |
| MOA Holdings Ltd | Health & social care | 2022 |
| Moba Property Investments Limited | Real estate | 2024 |
| Molmac Fire & Security Limited | Administrative & support | 2010 |
| Mond Medical Consulting Ltd | Health & social care | 2025 |
| Moneylocation Limited | Professional & scientific | 1999 |
| Monkeyjunk Ltd | Arts & recreation | 2025 |
| Monks Green Farm Limited | Real estate | 1961 |
| Montgo Biotech Limited | Professional & scientific | 2014 |
| Morenike Investments Ltd | Real estate | 2015 |
| Morgan Goodwood Investments Limited | Real estate | 2025 |
| Mortgage Syndicate Holdings Limited | Financial services | 2021 |
| Mortgage Syndicate PLC | Financial services | 2021 |
| Mortlake Capital Limited | Real estate | 2019 |
| Mosdak Ltd | Other services | 2019 |
| Motek (Vehicle Contracts) Limited | Transport & logistics | 1995 |
| MPM Construction Ltd | Construction | 2014 |
| MPW Consulting Ltd | Administrative & support | 2012 |
| MS Financial Limited | Information & communication | 2015 |
| MT Build Ltd | Construction | 2005 |
| Mthd Performance Systems Ltd | Arts & recreation | 2026 |
| Mtima Care Services Ltd | Health & social care | 2023 |
| Mtima Property Services Limited | Real estate | 2023 |
| Multipipe Limited | Wholesale & retail | 2012 |
| Multitubo Limited | Wholesale & retail | 2015 |
| Murfinn Ltd | Wholesale & retail | 2015 |
| Murton Enterprises UK Limited | Wholesale & retail | 2006 |
| MW Power Services Ltd | Professional & scientific | 2025 |
| My Local Cleaner Limited | Administrative & support | 2025 |
| Myals Consulting Services Limited | Professional & scientific | 2019 |
| Myers Jewellers Limited | Other services | 2024 |
| Mi̇tko Ltd | Hospitality | 2025 |
| N&L Drylining & Facades Limited | Construction | 2025 |
| N. Harrington Ltd | Health & social care | 2009 |
| Nacco Accounting Limited | Wholesale & retail | 2012 |
| Naendo UK Ltd | Information & communication | 2018 |
| Nails Salon Central Witham Ltd | Other services | 2024 |
| Napoli’S Finest Limited | Hospitality | 2025 |
| Natasha Corbin-Stewart Ltd | Professional & scientific | 2012 |
| Nathan Carr Consulting Limited | Professional & scientific | 2017 |
| National FPS Limited | Administrative & support | 2022 |
| National Performing Arts Summer Schools Limited | Education | 2024 |
| National Vehicle Traders Limited | Wholesale & retail | 2021 |
| Navara Group Limited | Professional & scientific | 2025 |
| Navidatum Limited | Information & communication | 2011 |
| Navigation Web Ltd | Information & communication | 2011 |
| Ndrive Automotive Ltd | Wholesale & retail | 2025 |
| Nedging SPV Ltd | Administrative & support | 2021 |
| Negotium Development Ltd | Professional & scientific | 2019 |
| Neil Smith Accountancy Limited | Professional & scientific | 2014 |