| Mark Gilbert Antiques Limited | Wholesale & retail | 2026 |
| Mark's Sharks Swim School Limited | Education | 2024 |
| MARKWICK16 LLP | | 2013 |
| Martinsley Management Company Limited | Households | 2014 |
| Martinsthorpe Utilities Limited | Construction | 2012 |
| Maruma Companionship Care Limited | Health & social care | 2026 |
| MAS DES PIC Ltd | Real estate | 2006 |
| Mashumba Limited | Hospitality | 2008 |
| Masida Solutions Ltd | Information & communication | 2021 |
| Mathias-Edmunds Properties Ltd | Real estate | 2023 |
| Mathshubx Ltd | Education | 2021 |
| Mawbrook Ltd | Construction | 2010 |
| MAX Accountants Ltd. | Professional & scientific | 2007 |
| MAX Wealth Accountants Ltd | Professional & scientific | 2020 |
| Maximist Limited | Administrative & support | 2022 |
| Mb-Ab Consulting Ltd | Professional & scientific | 2023 |
| MBO Performance Limited | Manufacturing | 2026 |
| MCA Salons Ltd | Other services | 2013 |
| Mcgeough Millinery Couture LLP | | 2018 |
| Mcgill Wealth Management Limited | Financial services | 2014 |
| Mchj Limited | Real estate | 2023 |
| Mcintoshmedia Ltd | Information & communication | 2013 |
| MCS Projects Limited | Education | 2003 |
| MD Spencer Limited | Health & social care | 2014 |
| Meadow View Dog Training and Paddock Ltd | Other services | 2023 |
| Meadows Executive Cars Limited | Transport & logistics | 1999 |
| Meadowsweet Farm Ltd | Hospitality | 2023 |
| Mecc Alte (UK) Limited | Manufacturing | 1997 |
| Mediatheme Limited | Arts & recreation | 2002 |
| Medichief Ltd | Extraterritorial | 2020 |
| Melton Mowbray Property Limited | Financial services | 2022 |
| Mercurius Operations Ltd | Financial services | 2026 |
| Meteor Impact Sockets Ltd | Wholesale & retail | 2013 |
| Metron F.M.C. Limited | Wholesale & retail | 2004 |
| MHR Estates Limited | Professional & scientific | 1997 |
| MHR International Emea Limited | Information & communication | 2012 |
| MHR International Holdings Limited | Information & communication | 2012 |
| MHR International Limited | Information & communication | 2012 |
| MHR Treasury Services Limited | Financial services | 2015 |
| Midlands Cabling and IT Services Ltd | Manufacturing | 2009 |
| Midwood Wines Ltd | Other services | 2019 |
| Mike Gould Sports Therapy Limited | Health & social care | 2020 |
| Miles Ahead Media Ltd | Information & communication | 2015 |
| Millington (Gallops Farm) Limited | Agriculture & fishing | 2004 |
| Millington Developments Limited | Real estate | 2004 |
| Millington Holdings Limited | Professional & scientific | 2003 |
| Mills 123 Holdings Limited | Financial services | 2025 |
| Mills Agricultural Limited | Agriculture & fishing | 2011 |
| Milne Property Management Ltd | Real estate | 2025 |
| Mini Monsters Soft Play Limited | Arts & recreation | 2010 |
| Mircare Ltd | Health & social care | 2015 |
| Mishka Creative Ltd | Administrative & support | 2020 |
| MJB Enterprises Limited | Professional & scientific | 2023 |
| MJW Rutland Limited | Health & social care | 2014 |
| MK 71 Management Limited | Hospitality | 2012 |
| Mlpj Holdings Ltd | Professional & scientific | 2023 |
| MMT Ltd | Information & communication | 1998 |
| MOA Consulting Ltd | Professional & scientific | 2023 |
| Mogara Ltd | Hospitality | 2023 |
| Moida Limited | Administrative & support | 2023 |
| Moonbase Holdings Ltd | Information & communication | 2025 |
| Moondrop Hotel Limited | Hospitality | 2020 |
| Moonfire Group Ltd | Real estate | 2026 |
| Moonflower Guitars Limited | Wholesale & retail | 2020 |
| Moore V Limited | Real estate | 2005 |
| Moresave Limited | Agriculture & fishing | 1997 |
| Morriss Motors Ltd | Wholesale & retail | 2020 |
| Morton Media Services Limited | Information & communication | 2017 |
| Mosdorfer CCL Systems Limited | Manufacturing | 1988 |
| Moss Architecture.Interiors Limited | Professional & scientific | 2003 |
| Mossbeath Commercial Holdings Ltd | Real estate | 2022 |
| Mowbray Workspace Solutions Ltd | Extraterritorial | 2024 |
| Mozir (UK) Limited | Professional & scientific | 2018 |
| MP Coaching Ltd | Education | 2022 |
| MP Mortgages Ltd | Financial services | 2016 |
| Mpcl Holding Company Limited | Financial services | 2022 |
| MPT Technical Engineering Ltd | Transport & logistics | 2016 |
| MRM Motors Ltd | Wholesale & retail | 2025 |
| MTK Vitality Limited | Health & social care | 2026 |
| MTP Mortgages Ltd | Financial services | 2026 |
| Multi Electrical Services Ltd | Manufacturing | 2020 |
| Multum GIN Parvo Limited | Professional & scientific | 1989 |
| Multum in Parvo Pubs Limited | Hospitality | 2025 |
| Multum in Parvo Ventures Limited | Professional & scientific | 2022 |
| Multum Limited | Extraterritorial | 2021 |
| Music Tour Services Ltd | Arts & recreation | 2022 |
| Myza Limited | Wholesale & retail | 2017 |
| N & P Travel Ltd | Transport & logistics | 2023 |
| N.C.T. & S. Limited | Manufacturing | 1973 |
| Nailspro 1 Ltd | Other services | 2024 |
| Nakota Tuwa UK Ltd | Wholesale & retail | 2022 |
| Namgrass UK Limited | Professional & scientific | 2009 |
| Nanev Holdings Limited | Financial services | 2023 |
| Naomiross Ltd | Professional & scientific | 2019 |
| Nathaniel Oliver & Associates Limited | Construction | 1976 |
| National Alliance Ltd | Other services | 2020 |
| Neema People CIC | Administrative & support | 2025 |
| Neptune Instrumentation Services Limited | Professional & scientific | 2007 |
| NET Zero Data Solutions Ltd | Extraterritorial | 2021 |
| NET Zero Reporting Ltd | Extraterritorial | 2021 |