| Mister Plug Ltd | Wholesale & retail | 2018 |
| Mitchell Auto Repairs Ltd | Wholesale & retail | 2025 |
| Mithil Property Ltd | Real estate | 2024 |
| Mitosis Retreats Limited | Hospitality | 2026 |
| MJB Property Group Ltd | Real estate | 2023 |
| MJC Promotions Limited | Professional & scientific | 2024 |
| MJD Plastics Ltd | Professional & scientific | 2013 |
| Mjdc (North East) Limited | Construction | 2016 |
| MJE Auto Tech and Recovery Ltd | Wholesale & retail | 2016 |
| MJM Grand Limited | Wholesale & retail | 2022 |
| MJS Motor Group Ltd | Wholesale & retail | 2025 |
| MK 2 JAF Barber Limited | Other services | 2024 |
| MK Properties (Sunderland) Ltd | Real estate | 2020 |
| Mk&Ds Kontrols Ltd | Manufacturing | 2026 |
| MKA Group Ltd | Administrative & support | 2025 |
| Mktconsult Ltd | Professional & scientific | 2025 |
| MLB (NE) Plumbing and Heating Ltd | Construction | 2021 |
| MLF Cages Ltd | Agriculture & fishing | 2024 |
| Mlse Ltd | Wholesale & retail | 2025 |
| MM Squared Holdings Limited | Financial services | 2025 |
| MMC Research & Marketing Ltd | Professional & scientific | 2016 |
| MNF Services Limited | Health & social care | 2017 |
| MNH Builders Ltd | Construction | 2025 |
| MO Integrated Service Ltd | Real estate | 2025 |
| Mobility Care Solutions Limited | Wholesale & retail | 2005 |
| Mobys Healthcare Ltd | Wholesale & retail | 2025 |
| Mocas Services Limited | Real estate | 2022 |
| Model Maker Space CIC | Arts & recreation | 2025 |
| Modern Property Investing Ltd | Education | 2024 |
| Modest Hijabz Ltd | Wholesale & retail | 2024 |
| Moduskills Ltd | Information & communication | 2024 |
| Molabido Fashion Ltd | Wholesale & retail | 2025 |
| Molloy Joinery & Construction Limited | Construction | 2015 |
| Molly's Tailored Trims Community Interest Company | Health & social care | 2025 |
| Momand Pizza Ltd | Hospitality | 2025 |
| Monarch Security Ltd | Administrative & support | 2026 |
| Monbu Ltd | Real estate | 2024 |
| Monbu Property Limited | Real estate | 2024 |
| Moncks Ltd | Manufacturing | 2024 |
| Mondita Ltd | Wholesale & retail | 2025 |
| Mondo Pizza North East Ltd | Hospitality | 2019 |
| Monkwearmouth Motor Company Limited | Wholesale & retail | 2025 |
| Monteirocruz Limited | Households | 2024 |
| Moorpark Limited | Extraterritorial | 1994 |
| Mordew Property Investments Ltd | Real estate | 2015 |
| Moretta Limited | Wholesale & retail | 2025 |
| Morharv Properties Limited | Real estate | 2005 |
| Morii Media Ltd | Professional & scientific | 2024 |
| Morni Ltd | Wholesale & retail | 2020 |
| Morpho Fitness Ltd | Other services | 2022 |
| Mortons Law Limited | Professional & scientific | 2014 |
| Mortons Law Nominees (NO. 1) Ltd | Professional & scientific | 2018 |
| Mortons Law Nominees (NO. 2) Ltd | Professional & scientific | 2018 |
| Moryson Consulting Ltd | Wholesale & retail | 2005 |
| Mosirham Limited | Manufacturing | 2022 |
| Motionfx Trading Ltd | Education | 2026 |
| Motiraj Limited | Hospitality | 2019 |
| Motrox Limited | Wholesale & retail | 2017 |
| Mount Daisy Ltd | Manufacturing | 2026 |
| Mouriél Ltd | Wholesale & retail | 2025 |
| Mouse's Industries Limited | Professional & scientific | 2021 |
| MP 1200 Limited | Real estate | 2022 |
| MP1201 Limited | Real estate | 2023 |
| MPC Sunderland Ltd | Hospitality | 2024 |
| MPL Property and Lettings Limited | Real estate | 2018 |
| MPS Homes Ltd | Real estate | 2018 |
| MR BIT Carpet and Upholstery Cleaning Ltd | Administrative & support | 2024 |
| MR Blue (NE) Ltd | Wholesale & retail | 2026 |
| MR Fonetastic Limited | Administrative & support | 2013 |
| MR Jacks Limited | Hospitality | 2019 |
| Mr.Munich Food Ltd | Hospitality | 2026 |
| Mreload PAY Ltd | Wholesale & retail | 2026 |
| MRH Properties (NE) Ltd | Real estate | 2024 |
| MRS Doubtflower Ltd | Wholesale & retail | 2025 |
| MS Khan Ltd | Wholesale & retail | 2025 |
| MS Organisation Ltd | Extraterritorial | 2024 |
| MTS Offshore Surveying Limited | Mining & quarrying | 2012 |
| Mullen Properties Limited | Real estate | 2003 |
| Mullers Limited | Manufacturing | 2006 |
| Mumbai Ashbrooke Ltd | Hospitality | 2018 |
| Mummy Mezze Limited | Hospitality | 2026 |
| Muni Ltd | Wholesale & retail | 2021 |
| Munlin Jopa Ltd | Health & social care | 2025 |
| Munster Developments Limited | Construction | 2018 |
| Murphys Leasure Limited | Hospitality | 2023 |
| Murton Pizza Ltd | Hospitality | 2022 |
| Musafari Ltd | Hospitality | 2021 |
| Mushben Ltd | Wholesale & retail | 2019 |
| Musi Prime Security Ltd | Transport & logistics | 2022 |
| Music City Ltd | Professional & scientific | 2024 |
| Mustardacc Ltd | Transport & logistics | 2022 |
| MVK Ltd | Hospitality | 2021 |
| Mvrk Properties Ltd | Real estate | 2025 |
| MW Properties NE Ltd | Real estate | 2024 |
| MW17 Consult Limited | Professional & scientific | 2025 |
| MWB Renewables Ltd | Manufacturing | 2025 |
| MWS Leisure Ltd | Arts & recreation | 2026 |
| My Delhi Sunderland Ltd | Hospitality | 2021 |
| My Games Ltd | Information & communication | 2025 |
| My Little Kingdom Day Nursery Limited | Health & social care | 2018 |