| Millavi Ltd | Wholesale & retail | 2022 |
| Millie Miles Event Hire Limited | Administrative & support | 2005 |
| Mills & Beau Limited | Manufacturing | 2025 |
| Milo Machines Ltd | Wholesale & retail | 2022 |
| Milton Blairgowrie Hotel Limited | Hospitality | 2019 |
| Milton Hotel and Leisure Group Limited | Hospitality | 2019 |
| MIM Project Services Limited | Construction | 2016 |
| Mindful Consultant Services Ltd | Professional & scientific | 2020 |
| Mindfunc Ltd | Information & communication | 2024 |
| Mindmosaic Limited | Professional & scientific | 2024 |
| Miologic Ltd | Wholesale & retail | 2023 |
| Mirada Studios Limited | Health & social care | 2025 |
| Miriam Vivian Ltd | Health & social care | 2012 |
| Miti Cook Ltd | Manufacturing | 2020 |
| Miyakawa Ltd | Professional & scientific | 2019 |
| Mizu Izakaya Limited | Hospitality | 2025 |
| Mizu Oxford Limited | Real estate | 2023 |
| Mizu Star Limited | Hospitality | 2026 |
| MJE Electrical Services Limited | Construction | 2014 |
| Mkgh Consulting Ltd | Health & social care | 2016 |
| Mkmortgages Ltd | Financial services | 2014 |
| Mlas Consulting Ltd | Information & communication | 2025 |
| Mlhj Building Services Limited | Construction | 2024 |
| Mmsio Ltd | Information & communication | 2019 |
| Mobiworks Limited | Information & communication | 2004 |
| MOCAP4 Ltd | Manufacturing | 2025 |
| Modal VR Ltd | Information & communication | 2021 |
| Modellaw Ltd | Information & communication | 2020 |
| Modern Butler Ltd | Administrative & support | 2024 |
| Modern Flat Roof Systems Ltd | Wholesale & retail | 2023 |
| Mohan Holdings Ltd | Real estate | 2020 |
| Moles Media Limited | Information & communication | 2020 |
| Momentum Mind Ltd | Administrative & support | 2024 |
| Monsuta Technology Limited | Wholesale & retail | 2026 |
| Montessori North Oxford Limited | Education | 2009 |
| Montys Burger Bars Ltd | Hospitality | 2021 |
| Moodle Design Limited | Manufacturing | 2023 |
| Moody Lighting Limited | Information & communication | 2012 |
| Moonshadow Farm Ltd | Agriculture & fishing | 2021 |
| Moral Kickboxing Ltd | Wholesale & retail | 2025 |
| Morban Limited | Professional & scientific | 2000 |
| Moreable Limited | Manufacturing | 2009 |
| Moreton Bathrooms Limited | Construction | 2009 |
| Morgan Accountancy Solutions Ltd | Professional & scientific | 2021 |
| Morris Perrin Insurance Consultants Limited | Financial services | 2019 |
| Morrison Property Consultants Ltd | Construction | 2010 |
| Morrison Property Holdings Ltd | Financial services | 2017 |
| Mortimore Electrical Services Limited | Construction | 2006 |
| Mossdale Ltd | Financial services | 2025 |
| Motion Asset Investors Limited | Financial services | 2021 |
| Motor Spirit Limited | Wholesale & retail | 2009 |
| Motorsport UK Association Limited | Arts & recreation | 1977 |
| Move in Matters Storage Solutions Ltd | Transport & logistics | 2019 |
| Movers NOT Shakers Ltd | Extraterritorial | 2006 |
| Moving Matters (National) Ltd | Transport & logistics | 2025 |
| Movocast Ltd | Information & communication | 2020 |
| Mowland Holdings Limited | Financial services | 2023 |
| Mowland Limited | Administrative & support | 2009 |
| MPA Property Investments Ltd | Real estate | 2024 |
| MPC Surveying Limited | Administrative & support | 2014 |
| MPE Tutors Limited | Education | 2018 |
| MPH Logistics Ltd | Transport & logistics | 2011 |
| MPL Technology Group Limited | Information & communication | 2004 |
| MPS Construction and Consultancy Ltd | Manufacturing | 2021 |
| MR FIX IT Limited | Construction | 2024 |
| MRB & Associates Ltd | Real estate | 2023 |
| MRB Martial Arts Ltd | Education | 2018 |
| Mrchntpymnts Limited | Other services | 2013 |
| MS Group Holdings Limited | Financial services | 2026 |
| MSF Properties Limited | Real estate | 2002 |
| MSJ Industries Ltd | Administrative & support | 2010 |
| MSW Design Limited | Professional & scientific | 2012 |
| MT Cargo Ltd | Transport & logistics | 2021 |
| MT Industrial Products Ltd | Wholesale & retail | 2019 |
| MTD (Great Britain) Limited | Extraterritorial | 1996 |
| MTD (UK) Limited | Extraterritorial | 1996 |
| MTD Corporation Limited | Extraterritorial | 1996 |
| MTD Europe Limited | Extraterritorial | 1996 |
| MTD Products Limited | Extraterritorial | 1996 |
| Mtech Access Holdings Limited | Professional & scientific | 2021 |
| Mtech Access Limited | Professional & scientific | 2015 |
| Mtech Analytics Limited | Financial services | 2015 |
| Mtkuk Ltd | Transport & logistics | 2014 |
| Muda Consulting Limited | Professional & scientific | 2007 |
| Mukwa Agricultural Limited | Professional & scientific | 2026 |
| Mulo Ltd | Education | 2023 |
| Mumma Sue's Limited | Hospitality | 2020 |
| Munin Property Ventures Ltd | Real estate | 2024 |
| Murimi Investment Group Ltd | Real estate | 2024 |
| Mushy Media Group Ltd | Professional & scientific | 2023 |
| Music at Your Service Limited | Arts & recreation | 2006 |
| Mvmt Collective Ltd | Wholesale & retail | 2025 |
| MW Audiotech Ltd | Manufacturing | 2018 |
| Mwesige Limited | Real estate | 2008 |
| MWH Elite Performance Centre Ltd | Arts & recreation | 2025 |
| MWH Interiors Limited | Construction | 2004 |
| MWP Construction Ltd | Construction | 2026 |
| My Lunchbox Meal Prep Ltd | Hospitality | 2019 |
| Mykaa Ltd | Wholesale & retail | 2022 |
| Mytex Limited | Information & communication | 2009 |