| M.Mozooni Ltd | Health & social care | 2022 |
| Mabea Investments Limited | Households | 2022 |
| Mach Auto Trading Limited | Wholesale & retail | 2024 |
| Made Entertainment UK Limited | Arts & recreation | 2022 |
| Madein Trading Ltd | Financial services | 2019 |
| Magda Fernandez EP Ltd | Education | 2025 |
| Magic Glass Ltd | Other services | 2017 |
| Magna Global Limited | Wholesale & retail | 2019 |
| Magnificat Partners Ltd | Professional & scientific | 2025 |
| Mahraz Limited | Real estate | 2007 |
| Mais Security Limited | Administrative & support | 2022 |
| Maliks Investments Limited | Financial services | 2024 |
| Mallmore UK Limited | Other services | 2016 |
| Mallu SOC Limited | Wholesale & retail | 2025 |
| Mandalay Apartments Management Limited | Real estate | 2020 |
| Mandalay Management Group Limited | Households | 2023 |
| Maniben LLP | | 2008 |
| Manifeston Ltd | Transport & logistics | 2023 |
| Mann and SON Property Limited | Real estate | 2017 |
| Mann Property Ventures Ltd | Real estate | 2025 |
| Mapal Limited | Manufacturing | 1993 |
| Mapna Properties Ltd | Real estate | 2021 |
| Mar-Ion Ltd | Construction | 2024 |
| Marco Polo International Limited | Administrative & support | 1996 |
| Mardi Landscape Services Ltd | Professional & scientific | 2019 |
| Margaret’S Accounting Ltd | Professional & scientific | 2018 |
| Mark Csit Ltd | Information & communication | 2020 |
| Mark International ED Consultancy UK Ltd | Education | 2025 |
| Markazi Imam Hussain Association | Professional & scientific | 2012 |
| Martin Mucha Ltd | Construction | 2019 |
| Massilia Properties Limited | Professional & scientific | 2006 |
| MAT LO Holdings Limited | Financial services | 2023 |
| Matale Service Limited | Construction | 2025 |
| Mater Design Limited | Wholesale & retail | 2022 |
| Materialize Zone Limited | Wholesale & retail | 2002 |
| Matthew's Healthcare Group Ltd | Other services | 2016 |
| Mattix Limited | Professional & scientific | 2021 |
| Mava Lifting Ltd | Construction | 2017 |
| MAX Robson Design Ltd | Professional & scientific | 2017 |
| Maximus Works Limited | Information & communication | 2014 |
| Maxtfs Limited | Professional & scientific | 2010 |
| Maxwell-Zak Ltd | Health & social care | 2020 |
| Maya Estates Ltd | Real estate | 2021 |
| Mbla Limited | Information & communication | 2017 |
| Mborio Ltd | Wholesale & retail | 2024 |
| Mbrg Limited | Professional & scientific | 2022 |
| MC Innovations Ltd | Professional & scientific | 2024 |
| MC Prime Developments Ltd | Construction | 2026 |
| Mcbride Maintenance Ltd | Construction | 2026 |
| Mckat Care Homes Ltd | Health & social care | 2020 |
| Mddx Ltd | Administrative & support | 2023 |
| MDZ Ltd | Real estate | 2020 |
| ME2A Happy Homes Limited | Real estate | 2021 |
| Mealplanme Group Ltd | Health & social care | 2019 |
| Mechanistic Labs Ltd | Information & communication | 2024 |
| Medisono Diagnostics Limited | Health & social care | 2026 |
| Melfort Ltd | Real estate | 2026 |
| Memotech Limited | Wholesale & retail | 1999 |
| Merabs Ltd | Hospitality | 2020 |
| Merrywood Ltd | Health & social care | 2023 |
| Metawoods Limited | Real estate | 2004 |
| Metro Management Services Limited | Construction | 2001 |
| MEW MMJ Holdings Ltd | Education | 2023 |
| MFT Film Limited | Information & communication | 2024 |
| MIC Construction Services Ltd | Construction | 2019 |
| Milford Blake London Ltd | Professional & scientific | 2020 |
| Million Foods Ltd | Wholesale & retail | 2023 |
| Millpit Furlong Management Company Limited | Households | 1988 |
| Milton Grange Limited | Wholesale & retail | 2004 |
| Mind Awareness Ltd | Health & social care | 2017 |
| Mind Tools for Kids Ltd | Education | 2015 |
| Minds Vision Ltd | Wholesale & retail | 2022 |
| Mindscape London Ltd | Public administration | 2024 |
| Mindwell Practice Ltd | Health & social care | 2026 |
| Minnie Media Limited | Information & communication | 2014 |
| Minutiae IT Ltd | Information & communication | 2023 |
| Mira's Beauty HUT Limited | Other services | 2025 |
| Miras Estates Limited | Real estate | 2022 |
| Mirava Education Ltd | Administrative & support | 1986 |
| Mirlees International Limited | Information & communication | 1985 |
| Miss LIZ Tutoring Ltd | Education | 2020 |
| Mitre Consult Limited | Professional & scientific | 2024 |
| MK Home Improvements Ltd | Other services | 2014 |
| Mmcy Business Solutions Ltd | Information & communication | 2018 |
| Mmotors JSC Limited | Wholesale & retail | 2009 |
| Mmvr Limited | Other services | 2024 |
| MOB 1 UK Ltd | Wholesale & retail | 2023 |
| Modern Bench Ltd | Manufacturing | 2022 |
| Modeva Studio Limited | Information & communication | 2024 |
| Momus Limited | Real estate | 2010 |
| Monetary Solutions Limited | Administrative & support | 2002 |
| Moneywise Financial Services Limited | Financial services | 2023 |
| Monisade Investments Limited | Real estate | 2018 |
| Montpelier Rosemont Management Limited | Real estate | 2008 |
| Moorexplore Group Ltd | Information & communication | 2026 |
| Morethan-Hr Ltd | Professional & scientific | 2014 |
| Moss Fresh UK Ltd | Manufacturing | 2022 |
| Motorvation UK Limited | Administrative & support | 2008 |
| Moyo Creative Ltd | Professional & scientific | 2018 |
| MS Atta Ltd | Health & social care | 2019 |