| Marketing Intuition Limited | Education | 2010 |
| Markets Direct Investments Limited | Other services | 2024 |
| Markets Direct Limited | Other services | 2013 |
| Marketsforce Limited | Financial services | 2018 |
| Marris Investments Ltd | Real estate | 2025 |
| Marshall Consult Ltd | Professional & scientific | 2016 |
| Marshall Pension & Financial Planning Ltd | Financial services | 2017 |
| Marshall Wind Solutions Ltd | Energy | 2024 |
| Marson Offshore Services Limited | Manufacturing | 2015 |
| Martin Clubb Development Limited | Professional & scientific | 2009 |
| Marvel Hall Limited | Administrative & support | 2021 |
| Mascalzone Limited | Hospitality | 2016 |
| Masonic Hall (Seaton Delaval) Limited | Other services | 1999 |
| Mass Engineering Ltd | Professional & scientific | 2018 |
| Mathology Ltd | Education | 2024 |
| Matrix Offshore Ltd | Professional & scientific | 2026 |
| Matt Ingram Structural Design Limited | Professional & scientific | 2007 |
| Maurell Projects Ltd | Real estate | 2023 |
| MBL Build Limited | Financial services | 2024 |
| Mc-Offshore Ltd | Manufacturing | 2014 |
| MCB Letting Ltd | Real estate | 2025 |
| MCB Wind Ltd | Energy | 2023 |
| Mccormick Access Solutions Ltd | Manufacturing | 2021 |
| Mcfarlane Tiling Services Limited | Construction | 2010 |
| MCH Electrics (North East) Ltd | Construction | 2007 |
| MCH Fitting Services Limited | Construction | 2006 |
| Mchugh & Co Financial Services Ltd | Financial services | 2025 |
| Mcla Productions Limited | Arts & recreation | 2025 |
| Mcqueen Medical Limited | Health & social care | 2022 |
| Mdst Consulting Ltd | Information & communication | 2019 |
| Mdstraining Limited | Education | 2020 |
| ME Global Resources Limited | Professional & scientific | 2021 |
| ME Project Management Limited | Professional & scientific | 2021 |
| ME Project Payroll Solutions Limited | Professional & scientific | 2021 |
| ME Property Holdings Ltd | Real estate | 2018 |
| Meadow View Property Limited | Financial services | 2021 |
| Meat Premier Outlet Limited | Wholesale & retail | 2019 |
| Medicines Manufacturing Centre LLP | | 2025 |
| Meghancare Ltd | Health & social care | 2024 |
| Melita Dental Practice Limited | Health & social care | 2012 |
| Melluna Ltd | Wholesale & retail | 2019 |
| Melrose Funeral Services Limited | Other services | 2007 |
| Mended Made Studios Ltd | Manufacturing | 2025 |
| Merry Events Catering Ltd | Hospitality | 2026 |
| Merrywell Care (Belmont Grange) Limited | Health & social care | 2021 |
| Merse Holdings Ltd | Financial services | 2025 |
| Merwave Limited | Wholesale & retail | 2020 |
| Messy Barber Ltd | Other services | 2024 |
| Metcalfes Wind Management Ltd | Administrative & support | 2025 |
| Metro Freight Services (U.K.) Limited | Transport & logistics | 1989 |
| MF Communications Rigging Services Ltd | Information & communication | 2019 |
| MG Financial Solutions NE Limited | Financial services | 2011 |
| MG Properties (NE) Limited | Real estate | 2025 |
| MGS - Mawdsley’S Gardening Services Ltd | Agriculture & fishing | 2026 |
| MH Highway & Transportation Services Ltd | Professional & scientific | 2007 |
| Mhbc Ltd | Hospitality | 2020 |
| Mhlweni Ltd | Information & communication | 2023 |
| Michael Ashburn Limited | Professional & scientific | 2009 |
| Middleton Court Management Company Limited | Real estate | 1997 |
| Mighty Lime Limited | Professional & scientific | 2015 |
| Mile Tavern Limited | Hospitality | 2025 |
| Milerose Limited | Professional & scientific | 1986 |
| Mill Gate (Wallsend) Management Company Limited | Households | 2007 |
| Miller Dragon Services Ltd | Professional & scientific | 2022 |
| Miller Family Farming Limited | Wholesale & retail | 2025 |
| Miller Family Investco Limited | Professional & scientific | 2014 |
| Minibit Limited | Information & communication | 2025 |
| Minoan Projects Ltd | Administrative & support | 2016 |
| Mint Finance (NE) Limited | Financial services | 2002 |
| Minvest Limited | Financial services | 2020 |
| Miomni Holdings Limited | Financial services | 2010 |
| Mistral Sailing Ltd | Arts & recreation | 2017 |
| Mitra Properties Ltd | Real estate | 2015 |
| MJ Wholesale Ltd | Wholesale & retail | 2023 |
| MJH Services NE Ltd | Health & social care | 2022 |
| MKJ Window Cleaning Ltd | Administrative & support | 2025 |
| MKW Electrical Contractors Ltd | Construction | 2017 |
| ML Fire Safety Solutions Ltd | Financial services | 2025 |
| ML2 Promotions Ltd | Professional & scientific | 2010 |
| MLC Wholesale Ltd | Hospitality | 2005 |
| MLJ Installations Holdings Limited | Extraterritorial | 2018 |
| MLQ Creative Solutions Ltd | Arts & recreation | 2013 |
| MM Bakery Ltd | Hospitality | 2025 |
| MNB Beauty Ltd | Other services | 2022 |
| MNM Estates Newcastle Ltd | Real estate | 2021 |
| Modera Bathrooms Ltd | Construction | 2025 |
| Modmo Ltd | Administrative & support | 2025 |
| Modrec Holdings Limited | Professional & scientific | 2007 |
| Modrec International Limited | Wholesale & retail | 1987 |
| Modulate Management Ltd | Professional & scientific | 2025 |
| Moor Court (Gosforth) Freehold Limited | Households | 2024 |
| Moore Hydraulic Services Limited | Extraterritorial | 2024 |
| More Movement Limited | Arts & recreation | 2018 |
| Morley Systems Limited | Information & communication | 1988 |
| Moss (North East) Limited | Real estate | 2024 |
| Motech Development Ltd | Information & communication | 2019 |
| Motoglaze Limited | Wholesale & retail | 2012 |
| MR BO Investments Limited | Financial services | 2021 |
| MR Property Investments Ltd | Hospitality | 2022 |
| MR Residential Holdings Limited | Households | 2022 |