| Matto Properties Limited | Real estate | 2023 |
| MAX Shearer Investments Ltd | Real estate | 2023 |
| MAX Shearer Property Ltd | Real estate | 2023 |
| MAX Shearer Property Management Ltd | Real estate | 2023 |
| Maxfield Properties Ltd | Real estate | 2022 |
| Maxtom Design Limited | Professional & scientific | 2006 |
| MAY Electrical Services Ltd | Construction | 2024 |
| Mayfair Land and Property Holdings Ltd | Financial services | 2021 |
| MB Global Alliance Ltd | Extraterritorial | 2022 |
| Mbne Installations Ltd | Construction | 2026 |
| MBS Pharma Limited | Health & social care | 2023 |
| Mcbrooke Ltd | Construction | 2026 |
| Mccartie Services Limited | Manufacturing | 2015 |
| Mccm Developments Limited | Hospitality | 2022 |
| Mccm Land Limited | Real estate | 2022 |
| Mccm Supply Limited | Administrative & support | 2022 |
| Mccormick & Harrington Limited | Health & social care | 2019 |
| Mccredie Family Holdings Ltd | Real estate | 2023 |
| Mccredie Family Partnership LLP | | 2023 |
| Mcculloch Bloodstock Partnership LLP | | 2022 |
| Mcgivney Holdings Ltd | Real estate | 2019 |
| Mcgivney Partnership LLP | | 2019 |
| Mckenna Advanced Technology Ltd | Other services | 2015 |
| Mckenziee Limited | Wholesale & retail | 2025 |
| Mcnicholas Estates Ltd. | Real estate | 1998 |
| Mcnicholas Group (Holdings) Limited | Financial services | 1997 |
| Mcnicholas Homes Limited | Construction | 1983 |
| Mcnicholas Limited | Real estate | 2008 |
| MDL Metals Ltd | Manufacturing | 2020 |
| MDS Environmental Services Ltd | Construction | 2006 |
| Meadowvale Funeral Services Ltd | Other services | 2021 |
| Meadowvale Homecare Ltd | Health & social care | 2014 |
| Mech Enabling Ltd | Administrative & support | 2023 |
| Medical Therapies Ltd | Health & social care | 2012 |
| Medics Care UK Limited | Health & social care | 2024 |
| Medvantage Limited | Health & social care | 2025 |
| Meemaw Limited | Other services | 2021 |
| Meera Shaunak LLP | | 2019 |
| Mehra Family Partnership LLP | | 2020 |
| MEL Betsho Ltd | Professional & scientific | 2026 |
| Melissa's Solutions Limited | Wholesale & retail | 2026 |
| Melrose Medical Centre Limited | Health & social care | 2009 |
| Melt and Pickle Ltd | Hospitality | 2021 |
| Merstona Ltd | Other services | 2010 |
| Mesh Marketing Limited | Professional & scientific | 2004 |
| Mesh Supplies & Fabrications Limited | Manufacturing | 2015 |
| Metin Medical Limited | Health & social care | 2025 |
| Mets Services Limited | Construction | 2003 |
| MG Seller Ltd | Wholesale & retail | 2024 |
| Mglm (PI) Ltd | Real estate | 2022 |
| Mglm Limited | Administrative & support | 2013 |
| Mglx Partnership LLP | | 2023 |
| Mglx Rentals Ltd | Real estate | 2019 |
| MGR Electrical Services Ltd | Construction | 2020 |
| MGR Trade Limited | Wholesale & retail | 2024 |
| Mhbp Family Holdings Limited | Real estate | 2021 |
| Mhbp Family Partnership LLP | | 2021 |
| MHS Properties Partnership LLP | | 2019 |
| Michael Mitchell Developments Ltd | Construction | 2020 |
| Microtechnics Consultants Limited | Information & communication | 2011 |
| Mike Stone Properties Ltd | Real estate | 2019 |
| Mill House Property Holdings Ltd | Real estate | 2021 |
| Mill House Property Partnership LLP | | 2021 |
| Mill Lane (Billingham) Ltd | Wholesale & retail | 2024 |
| Millbrook Ltd | Real estate | 2023 |
| Millennium Nails Europe Limited | Wholesale & retail | 2017 |
| Millfield UK Properties Limited | Real estate | 2015 |
| Milligan Family Holdings Ltd | Real estate | 2023 |
| Milligan Family Partnership LLP | | 2023 |
| Milou Engineering Ltd | Professional & scientific | 2023 |
| Mima Brothers Ltd | Hospitality | 2025 |
| Mimos Billingham Ltd | Hospitality | 2020 |
| Mindey Ltd | Information & communication | 2022 |
| Mindflow Audio Ltd | Arts & recreation | 2025 |
| Mindset Counselling Services Ltd | Education | 2021 |
| Mini WAX Melts Ltd | Manufacturing | 2018 |
| Minnear Family Holdings Ltd | Real estate | 2019 |
| Minnear Family Partnership LLP | | 2019 |
| Mino-Md Limited | Health & social care | 2022 |
| Miracle Mansions Limited | Real estate | 2018 |
| Miracle Property Ltd | Real estate | 2014 |
| Miracle Property Partnership LLP | | 2020 |
| Mitchell's Family Partnership LLP | | 2020 |
| Mitchell's Rental Properties Ltd | Real estate | 2013 |
| Mitchells Freeholdings Ltd | Real estate | 2024 |
| Mixology Music Ltd | Arts & recreation | 2013 |
| MIY Developments Ltd | Construction | 2024 |
| MJC Services (NE) Ltd | Administrative & support | 2012 |
| Mjjh Contracts Limited | Professional & scientific | 2014 |
| MJN Burdon Ltd | Information & communication | 2015 |
| ML Civil ENG Ltd | Construction | 2015 |
| MLA Industrial Ltd | Manufacturing | 2023 |
| MLJ Lighting Limited | Wholesale & retail | 2017 |
| MLL Electrical Ltd | Construction | 2026 |
| MM Sisters Limited | Real estate | 2026 |
| MO Money Global Ltd | Professional & scientific | 2025 |
| Mogridgelettings Limited | Real estate | 2016 |
| Moli Properties Limited | Real estate | 2019 |
| Molihomes Family Partnership LLP | | 2020 |
| Mollisaa & George Ltd | Real estate | 2019 |