| Mark Reed Building Services Limited | Construction | 2003 |
| Market Bosworth Personal Training Services Limited | Other services | 2011 |
| Marketing IQ Limited | Professional & scientific | 2005 |
| Marlen Ltd | Real estate | 2026 |
| Marnie Property Ltd | Real estate | 2022 |
| Maroon London Management Limited | Professional & scientific | 2015 |
| Marriott Group Limited | Financial services | 2001 |
| Marriott Haulage Limited | Transport & logistics | 2007 |
| Marriott Land & Estate Ltd | Real estate | 2001 |
| Marriott Leisure Limited | Extraterritorial | 2022 |
| Marriott Plant Limited | Extraterritorial | 2012 |
| Marriott Real Estate Ltd | Real estate | 2020 |
| Marriott Rental Ltd | Extraterritorial | 2001 |
| Marriott Services Limited | Manufacturing | 2024 |
| Martial Arts Licensing Ltd | Professional & scientific | 2021 |
| Martin John Engineering Services Limited | Professional & scientific | 2019 |
| Martin Logue Limited | Health & social care | 2006 |
| Marula Consultancy Ltd | Education | 2018 |
| Masterflow UK Limited | Manufacturing | 2009 |
| Match Supplies Ltd | Wholesale & retail | 2022 |
| Mateo Transped Ltd | Transport & logistics | 2018 |
| Material Barn Ltd | Extraterritorial | 2020 |
| Mathi OLI Ltd | Health & social care | 2020 |
| Matthew H Robinson Ltd | Construction | 2009 |
| Maya Medicine Ltd | Other services | 2011 |
| Mayband Lettings Limited | Real estate | 2003 |
| Mayband Property Limited | Real estate | 1997 |
| Mayke Limited | Extraterritorial | 2013 |
| Mayoak Properties Limited | Real estate | 2014 |
| MBF Group Ltd | Professional & scientific | 2020 |
| Mbrc Medical Ltd | Health & social care | 2016 |
| Mcashwey Stud Limited | Agriculture & fishing | 2017 |
| Mccarthy Medical Limited | Other services | 2012 |
| Mcgavin Consulting Ltd | Professional & scientific | 2025 |
| MD Digital Solutions Ltd | Information & communication | 2026 |
| MDD Developments Ltd | Financial services | 2015 |
| MED Group Incorporated Limited | Wholesale & retail | 2005 |
| MED Race Technologies Limited | Administrative & support | 2007 |
| Medeor Surgery Ltd | Health & social care | 2022 |
| Medi Praise Aesthetics Ltd | Health & social care | 2020 |
| Medi-Laser Solutions Limited | Health & social care | 2005 |
| Media Duplication Limited | Manufacturing | 2008 |
| Media Film Productions Limited | Information & communication | 2021 |
| Medical Design Solutions Limited | Other services | 2021 |
| Melior Golf Limited | Professional & scientific | 2016 |
| Melm Care Solutions Ltd | Health & social care | 2018 |
| Melm Properties Ltd | Real estate | 2020 |
| Mercia Evolution General Partner LLP | | 2025 |
| Mercia Evolution Holdco Limited | Financial services | 2025 |
| Meta Displays Ltd | Professional & scientific | 2024 |
| Metal Adder Ltd | Information & communication | 2025 |
| Metalways Agriculture Ltd | Agriculture & fishing | 2013 |
| Mewp Finder Ltd | Information & communication | 2025 |
| Meyrick Smithson Limited | Professional & scientific | 2020 |
| Mezes Imaging Ltd | Wholesale & retail | 2016 |
| MF Contractors Ltd | Construction | 2014 |
| Mfcube Consulting Limited | Information & communication | 2015 |
| MH Controls Ltd | Information & communication | 2026 |
| Michael a FOX Associates Ltd | Professional & scientific | 2015 |
| Michael Fairfield Limited | Other services | 2009 |
| Michael Stuart Upholstery Limited | | 1987 |
| Michal C Motors Ltd | Wholesale & retail | 2025 |
| Mickleburgh and Rutland Limited | Wholesale & retail | 1961 |
| Microserve Ltd | Information & communication | 2024 |
| Midaset Separates (Leicester) Limited | | 1980 |
| Middle Farm Crafts Ltd | Other services | 2020 |
| Midland Domestic Services Ltd | Construction | 1999 |
| Midland Engineering Ltd | Professional & scientific | 2024 |
| Midland GUN Company Limited | Extraterritorial | 2016 |
| Midland Philatelics Ltd | Wholesale & retail | 2010 |
| Midland Window Maintenance Limited | Other services | 2007 |
| Midlands Cooling Services Ltd | Other services | 2014 |
| Midlands Lets Limited | Real estate | 2013 |
| Midtech Control Systems Limited | Professional & scientific | 2024 |
| Mike Norwood Ltd | Health & social care | 2018 |
| Miles Brothers Motors Ltd | Wholesale & retail | 2022 |
| Miles Getaways Ltd | Hospitality | 2025 |
| Miles Patisserie Ltd | Manufacturing | 2024 |
| Miles's Ltd | Hospitality | 2025 |
| Military Mail Limited | Wholesale & retail | 2012 |
| Millbrook Conferences and Events Limited | Administrative & support | 2022 |
| Miller Mckenna Ltd | Professional & scientific | 2016 |
| Millwood Rubber Co. Limited | | 1947 |
| Mindful Here and There Limited | Health & social care | 2024 |
| Minerva Medical Ltd | Manufacturing | 2019 |
| Mini Healthcare Heroes Limited | Arts & recreation | 2023 |
| Mini Minds Childminding Limited | Health & social care | 2025 |
| Mintblue Properties Limited | Real estate | 2004 |
| Mirengo Developments Limited | Real estate | 2025 |
| Mirengo Limited | Professional & scientific | 2015 |
| Misterton Modelling Services Limited | Other services | 2002 |
| Mitchellwest Group Ltd | Extraterritorial | 2006 |
| Mitchellwest Ltd | Manufacturing | 2003 |
| Mitchellwest Technical Services Ltd | Extraterritorial | 2006 |
| MJC Chen Ltd | Hospitality | 2016 |
| MK Kitchens and Bathrooms Ltd | Manufacturing | 2019 |
| MKT Trading Limited | Construction | 2024 |
| Mlma Properties Ltd | Real estate | 2024 |
| Mmmm & Co Limited | Health & social care | 2019 |
| Mobile Hydraulics Limited | Other services | 1997 |