| Mars Anaesthesia Ltd. | Health & social care | 2019 |
| Mart and Mall Ltd | Professional & scientific | 2023 |
| Martin Phelps Music Limited | Wholesale & retail | 1995 |
| Martin's Mill Management Company Ltd | Households | 1998 |
| Masdaq Ltd | Real estate | 2018 |
| Mason Design & Research Studio Limited | Professional & scientific | 2024 |
| Masons Microbars LLP | | 2014 |
| Master Hand Services Ltd | Manufacturing | 2021 |
| Mastercam UK Limited | Wholesale & retail | 2022 |
| Mastermind Electronics Limited | Other services | 2011 |
| Masters Wood Working Ltd | Manufacturing | 2021 |
| Mat's Windows Ltd | Construction | 2023 |
| Match Fit Property Services Ltd | Administrative & support | 2023 |
| Matchen Ltd | Information & communication | 2026 |
| Matharu Delivery Service Ltd | Transport & logistics | 2012 |
| Matthew Partridge Ltd | Hospitality | 2016 |
| Matthews Education Consulting Ltd | Education | 2026 |
| Mattress Wholesale Limited | Wholesale & retail | 2016 |
| Mawandis Ltd | Health & social care | 2011 |
| Maws (Services) Ltd | Water & waste | 2016 |
| MAX Empire Capitals Ltd | Financial services | 2025 |
| MAX Empire Properties Ltd | Construction | 2025 |
| Maxair Ltd | Construction | 2017 |
| Maxgrace Property Ltd | Real estate | 2018 |
| Maxipay Ltd | Professional & scientific | 2021 |
| Maxitron Limited | Wholesale & retail | 1997 |
| Maxpower Services Limited | Manufacturing | 2016 |
| Maxrock Studios Limited | Arts & recreation | 2020 |
| Mayfair Fine Watches Limited | Wholesale & retail | 2023 |
| Mazari Investments Ltd | Real estate | 2024 |
| MB Bikes Ltd | Wholesale & retail | 2011 |
| MB Installation & Sons Ltd | Construction | 2025 |
| Mcarpenters Ltd | Construction | 2022 |
| Mccamley UK Limited | Manufacturing | 2011 |
| Mccarron Enterprises Carlisle Limited | Real estate | 2010 |
| Mccarron Enterprises Domestic Ltd | Households | 2021 |
| Mccarthy Stewart Ltd | Professional & scientific | 2024 |
| MCD Project Management Ltd | Information & communication | 2010 |
| Mckalias Health Professionals Limited | Health & social care | 2015 |
| MCN Steel Fixing Limited | Construction | 2019 |
| Mcr&A Limited | Professional & scientific | 2023 |
| Mcrs (Midlands) Limited | Manufacturing | 2023 |
| MCT Heating Services Ltd | Construction | 2006 |
| MD Building Group Ltd | Construction | 2020 |
| MDB Ceilings & Partitions Limited | Construction | 2008 |
| MDB Developments & Construction Limited | Construction | 2021 |
| Mdvcoding Ltd | Information & communication | 2020 |
| Mecovia Ltd | Manufacturing | 2026 |
| Medi RX Ltd | Health & social care | 2021 |
| Mediahut Limited | Real estate | 2000 |
| Mediaid Care Services Ltd | Education | 2014 |
| Mediamedica Ltd | Education | 2020 |
| Medicolegal Expert Reports Limited | Health & social care | 2021 |
| Mediease Ltd | Wholesale & retail | 2024 |
| Meds Online 247 Limited | Wholesale & retail | 2019 |
| Mega Scaffold (UK) Limited | Construction | 2008 |
| Megwheat Ltd | Hospitality | 2025 |
| Melanie Unwin Independent Funeral Directors Limited | Other services | 2025 |
| Melimatic Limited | Manufacturing | 1982 |
| Meliora Aesthetics Ltd | Health & social care | 2026 |
| Mellow Accountants LLP | | 2009 |
| Mellow Designs Limited | Construction | 2002 |
| Memluk Property Ltd | Real estate | 2026 |
| Mena Engineering Limited | Manufacturing | 2002 |
| Mendicant Consultancy Services Ltd | Professional & scientific | 2020 |
| Mercado Central Limited | Hospitality | 2018 |
| Mercer Knight Limited | Real estate | 2025 |
| Merchandise Store Ltd | Wholesale & retail | 2022 |
| Merchants Premium Food Ltd | Wholesale & retail | 2024 |
| Merchantsdise Ltd | Wholesale & retail | 2024 |
| Mercia Innovation Partners Ltd | Administrative & support | 2023 |
| Mercury Bearings Limited | Wholesale & retail | 1998 |
| Mercury Holdings (London) Limited | Professional & scientific | 2009 |
| Merry Hill QSR (NO. 1) Limited | Hospitality | 2019 |
| Merry Hill QSR (NO. 2) Limited | Hospitality | 2019 |
| Mersona Limited | Manufacturing | 1968 |
| Metal Fusion Technology Limited | Manufacturing | 2003 |
| Metering and Leak Detection Services Ltd | Professional & scientific | 2023 |
| Metrium Special Metals Limited | Wholesale & retail | 2020 |
| Metro Alloys & Residues Limited | Water & waste | 1985 |
| MEW Utilities Ltd | Professional & scientific | 2026 |
| MEX Hustles Limited | Wholesale & retail | 2025 |
| MFS Holdings Limited | Real estate | 2019 |
| MG Steels Limited | Wholesale & retail | 1990 |
| MGA Financial Planning Limited | Financial services | 2000 |
| Mgwp Holdings Limited | Financial services | 2012 |
| MH Camps Limited | Health & social care | 2024 |
| MHA Europe Limited | Wholesale & retail | 2016 |
| Mhprime View Ltd | Wholesale & retail | 2026 |
| MHQ Properties Ltd | Real estate | 2025 |
| Michelle Hair Salon Limited | Other services | 2025 |
| Michelle Penelope Consulting Limited | Professional & scientific | 2021 |
| Midco Limited | Real estate | 1991 |
| Midland Accountancy Group Limited | Professional & scientific | 2009 |
| Midland Audio X-Change Limited | Wholesale & retail | 2003 |
| Midland Auto Craft Ltd | Wholesale & retail | 2004 |
| Midland Digital Ltd | Information & communication | 2025 |
| Midland Drivers Limited | Administrative & support | 2014 |
| Midland Environmental LLP | | 2009 |
| Midland Fittings Limited | Wholesale & retail | 1985 |