| Masterclass Tiling and Plumbing Ltd | Construction | 2026 |
| MAT NAT Ltd | Arts & recreation | 2018 |
| Matchsaver Limited | Extraterritorial | 2025 |
| Materials Processing Institute | Professional & scientific | 2014 |
| Maths & Science Academy Limited | Education | 2022 |
| Matrix Process Ltd | Professional & scientific | 2026 |
| Mattertest Ltd | Professional & scientific | 2025 |
| Matthew Brown Blacksmiths Limited | Manufacturing | 2003 |
| Matthew Fletcher Golf Ltd | Education | 2024 |
| Matthew Ridley Ltd | Transport & logistics | 2026 |
| Matthew Thirlwall Technical Services Limited | Professional & scientific | 2013 |
| Matthew Webb Knowledge Limited | Extraterritorial | 2018 |
| Matthew Wilkinson Solicitors Limited | Professional & scientific | 2011 |
| Matthews Property (NE) Ltd | Real estate | 2022 |
| Maval Electrical and Mechanical Engineering Company Limited | Construction | 1972 |
| Maval Holdings Limited | Financial services | 2023 |
| Mavas Foods Limited | Hospitality | 2020 |
| Mavurayi SG Ltd | Health & social care | 2020 |
| Mawg Consulting Limited | Professional & scientific | 2015 |
| MAX Gibb Building Services Limited | Construction | 2022 |
| MAX Rigging Ltd | Construction | 2017 |
| MAX Training Academy Ltd | Arts & recreation | 2013 |
| Maxam Industries Ltd | Manufacturing | 2023 |
| Maxi Site Services Limited | Construction | 2025 |
| Maxi Taxi Limited | Professional & scientific | 2011 |
| Maxi Taxi NE Ltd | Transport & logistics | 2024 |
| Maxisoft Tech Ltd | Information & communication | 2025 |
| Maxscaff Solutions Ltd | Construction | 2025 |
| Maxt Site Services Ltd | Professional & scientific | 2018 |
| Maxtread Tyre & Autocare Ltd | Extraterritorial | 2018 |
| Maxwell Motors North East Limited | Wholesale & retail | 2025 |
| Mayas Living Ltd | Hospitality | 2025 |
| Mayor AJ Couture Limited | Professional & scientific | 2025 |
| Mayq Tech Ltd | Wholesale & retail | 2022 |
| Maythorne Properties (Stokesley) Limited | Financial services | 2015 |
| Mazetaverna Greek Ltd | Hospitality | 2026 |
| MB Commercial Properties Ltd | Construction | 2022 |
| MB Contract Solutions Ltd | Professional & scientific | 2026 |
| MB Flooring Contractors Ltd | Construction | 2021 |
| MB Holdco Ltd | Financial services | 2022 |
| MB Offshore Consultants Ltd | Other services | 2013 |
| MB Plating Services Limited | Construction | 2012 |
| Mb-Cindstrial Limited | Professional & scientific | 2026 |
| MBA Wholesale Ltd | Wholesale & retail | 2025 |
| MBAOK01 Limited | Construction | 2025 |
| MBAOK02 Limited | Hospitality | 2025 |
| Mbc.Supplies Ltd | Professional & scientific | 2025 |
| Mbgroupamz Ltd | Wholesale & retail | 2025 |
| Mborocars Ltd | Wholesale & retail | 2025 |
| Mbro Top Class Cars Ltd | Wholesale & retail | 2025 |
| Mbro Traders Ltd | Hospitality | 2026 |
| Mbro Trading Ltd | Wholesale & retail | 2021 |
| Mbuksrock Group Ltd | Transport & logistics | 2026 |
| MC Carpentry Services Ltd | Manufacturing | 2022 |
| MC Rooftec Home Improvements Limited | Construction | 2021 |
| MC Trade Center Ltd | Wholesale & retail | 2026 |
| Mcavoy LGS Limited | Professional & scientific | 2024 |
| MCB Mechanical Inspection Limited | Professional & scientific | 2011 |
| Mcblakeley Ltd | Wholesale & retail | 2025 |
| Mcbride Heavy Lifting Ltd | Construction | 2025 |
| Mcculloch Engineering Services Limited | Professional & scientific | 2020 |
| Mcdonald Maritime Ltd | Transport & logistics | 2023 |
| Mcdonnell Mechanical Design Limited | Professional & scientific | 2007 |
| Mcgee and Rizon Ltd | Real estate | 2022 |
| Mcgee Mcgee Agar Law Limited | Professional & scientific | 2018 |
| Mcgee Mcgee Agar Properties Limited | Real estate | 2025 |
| Mcginley Financial Ltd | Professional & scientific | 2019 |
| Mcguinness ROV Services Ltd | Other services | 2023 |
| Mcivor Longdon Surplus Solutions Ltd | Wholesale & retail | 2025 |
| MCK 247 Ltd | Administrative & support | 2025 |
| Mckenna Access Ltd | Construction | 2022 |
| Mcla Developments Ltd | Manufacturing | 2024 |
| Mclaney Developments Limited | Construction | 2002 |
| Mclaney Lettings Limited | Real estate | 2008 |
| Mclb Developments Ltd | Households | 2024 |
| Mclb Leases Ltd | Real estate | 2024 |
| Mcleod Access Solutions Ltd | Construction | 2026 |
| Mcnice Creations Ltd | Information & communication | 2024 |
| Mcquilling Engineering Solutions Ltd | Professional & scientific | 2018 |
| MCR Personal Ltd | Administrative & support | 2023 |
| MCW UK Solutions Ltd | Professional & scientific | 2025 |
| Mcwood Property Management & Lettings Limited | Real estate | 2020 |
| MD Lifting Services Ltd | Construction | 2022 |
| MD5 Forensics Ltd | Professional & scientific | 2012 |
| MD5 Ltd | Professional & scientific | 2003 |
| MD5 Software Ltd | Information & communication | 2024 |
| Mdaggett Ltd | Professional & scientific | 2023 |
| MDD Motorsport Limited | Administrative & support | 2026 |
| MDD UK Group Ltd | Administrative & support | 2025 |
| MDG Instruments Ltd | Professional & scientific | 2017 |
| Mdjb (UK) Ltd | Construction | 2018 |
| Mdjd Property Limited | Real estate | 2021 |
| MDM Carpentry Ltd | Construction | 2024 |
| MDM Joinery NE Ltd | Construction | 2023 |
| Mdmbro Ltd | Construction | 2026 |
| Mdobs Ltd | Financial services | 2022 |
| Mdolly Limited | Wholesale & retail | 2026 |
| MDP21 Ltd | Health & social care | 2019 |
| MDS Energy Ltd | Wholesale & retail | 2019 |
| MDW Diamond Housing Ltd | Real estate | 2021 |