| Mansonk Limited | Wholesale & retail | 2025 |
| Mantis Media Ltd | Professional & scientific | 2014 |
| Mar-Haulage Limited | Transport & logistics | 2017 |
| Marc Powsey Services Ltd | Professional & scientific | 2017 |
| Marfen Homes Limited | Construction | 2015 |
| Marfen Scarborough Limited | Construction | 2016 |
| Mark Lockey Site Services Ltd | Construction | 2013 |
| Martin Royce Geddes Limited | Extraterritorial | 2022 |
| Maximus Embedded Ltd | Professional & scientific | 2021 |
| May-Ko Finance Ltd | Financial services | 2026 |
| MCC (2022) Holdings Limited | Financial services | 2022 |
| Mckay Property Services Limited | Real estate | 2019 |
| Mckay Rental Ltd | Real estate | 2024 |
| Mckenzie Music Limited | Arts & recreation | 2008 |
| Mcpherson Joinery Services Limited | Construction | 2015 |
| Mcpherson Rope Access (MRA) Ltd | Construction | 2024 |
| MDH Commerce Ltd | Wholesale & retail | 2026 |
| Mech Mentor Solutions Training Ltd | Education | 2025 |
| Meowve - Teesside Ltd | Professional & scientific | 2022 |
| MEP BID Management Ltd | Professional & scientific | 2020 |
| Merciful Care Ltd | Health & social care | 2025 |
| Mercury Fuel Systems Limited | Manufacturing | 2008 |
| Meridian Upholstery (Group) Ltd | Real estate | 2019 |
| Meridian Upholstery Limited | Manufacturing | 2013 |
| Metrick Limited | Real estate | 2021 |
| MFM Tyres Ltd | Wholesale & retail | 2026 |
| Middleton Waters Management Company Limited | Households | 2021 |
| Middridge Manufacturing Limited | Construction | 2016 |
| Midland Structural Services (Northern) Limited | Professional & scientific | 1996 |
| Mike's Fish Bar Ltd | Hospitality | 2019 |
| Millbrand Music Limited | Extraterritorial | 2015 |
| Mint Barbers Limited | Other services | 2014 |
| Missedabeat Services Limited | Manufacturing | 2024 |
| MJ Armstrong Associates Ltd | Information & communication | 2010 |
| MJ Lifestyle Vans Ltd | Wholesale & retail | 2023 |
| MJK Holdings Ltd | Real estate | 2026 |
| MJR Classic Cars Ltd | Wholesale & retail | 2024 |
| MK Plant & Machinery Sales (UK) Ltd | Wholesale & retail | 2017 |
| Mmm&E Limited | Financial services | 2021 |
| Mobile Rocket Limited | Information & communication | 2010 |
| Modern Facade Solutions Ltd | Manufacturing | 2024 |
| Modevine Ltd | Health & social care | 2022 |
| Molekula Limited | Wholesale & retail | 2009 |
| Montana Systems Ltd | Wholesale & retail | 2025 |
| Moodie Financial Consulting Ltd | Professional & scientific | 2017 |
| Moreburger Ltd | Hospitality | 2021 |
| Motion Airsports Ltd | Arts & recreation | 2026 |
| Motorfix Auto Repairs Limited | Wholesale & retail | 2021 |
| Movix Logistics Ltd | Transport & logistics | 2025 |
| MR Glass Replacements Ltd | Construction | 2026 |
| MRM Properties (Newton Aycliffe) LLP | | 2014 |
| MSC Rope Technician Ltd | Construction | 2024 |
| MT Holdings NE Ltd | Financial services | 2019 |
| MTM Transport Limited | Construction | 2016 |
| Mucker Swan Ltd | Administrative & support | 2022 |
| Multi Tech Limited | Manufacturing | 2017 |
| Multi-Surface Fabrications Limited | Manufacturing | 2001 |
| MVP Performance and Well-Being Limited | Other services | 2020 |
| Myla 17 Limited | Administrative & support | 2022 |
| N.P Fleet Services Ltd | Wholesale & retail | 2022 |
| Nails by Abbi Ltd | Other services | 2023 |
| NAM Site Engineering Limited | Administrative & support | 2014 |
| Nanorisk Limited | Information & communication | 2021 |
| NAS Group Durham Limited | Transport & logistics | 2003 |
| NAS Recruitment Services Limited | Extraterritorial | 2014 |
| NAS Transport Services Limited | Extraterritorial | 2014 |
| Nationwide Leisure Homes Limited | Construction | 2018 |
| Nbellwood Ltd | Professional & scientific | 2023 |
| NC Group Ltd | Professional & scientific | 2017 |
| NC Holdings (North East) Ltd | Financial services | 2022 |
| NC Properties (North East) Ltd | Real estate | 2022 |
| Neesam Properties Ltd | Households | 2022 |
| Neilz Ltd | Wholesale & retail | 2024 |
| Nestiq Properties Ltd | Real estate | 2025 |
| Newton Aycliffe Sports Club Limited | Arts & recreation | 2023 |
| Newton Aycliffe Workwear Supplies Ltd | Wholesale & retail | 2017 |
| Newton Fast Foodd Ltd | Hospitality | 2026 |
| Next Level Building & Joinery Services Ltd | Construction | 2025 |
| NFI Developments Limited | Real estate | 2025 |
| Niloc Property Services Ltd | Construction | 2018 |
| Nima's Barbers Ltd | Other services | 2026 |
| NK Solution Ltd | Manufacturing | 2025 |
| Nkit Build Ltd | Construction | 2025 |
| Non-Destructive-Testing.Com Limited | Manufacturing | 2017 |
| North East Development Group Ltd. | Wholesale & retail | 2015 |
| North East Joiners Ltd | Construction | 2017 |
| North East Pizza Ltd | Hospitality | 2022 |
| North East Property & Maintenance Services Limited | Administrative & support | 2018 |
| North East Psychology Services Limited | Health & social care | 2007 |
| North East Sealants Limited | Construction | 2022 |
| North East Truck and Driver Ltd. | Transport & logistics | 2017 |
| North England Laboratory Supplies Ltd | Administrative & support | 2000 |
| Northcote Holdings (SE) Ltd | Financial services | 2024 |
| Northern Counties Business Services Limited | Transport & logistics | 2004 |
| Northern Music Centre Ltd | Education | 2009 |
| Northern Power Clean Limited | Administrative & support | 1989 |
| Northern Property Services NE Limited | Real estate | 2018 |
| Northern Structural Solutions Ltd | Professional & scientific | 2025 |
| Northern Waste Recycling Ltd | Water & waste | 2016 |
| Northgate Signature Ltd | Real estate | 2015 |