| MGB Teesside Ltd | Wholesale & retail | 2018 |
| MGD Engineering Services Ltd | Professional & scientific | 2024 |
| MGF Asset Finance Ltd | Financial services | 2013 |
| MGL Wind Services Ltd | Manufacturing | 2025 |
| Mhtech Engineering Ltd | Professional & scientific | 2017 |
| Miami Holdings Limited | Real estate | 2017 |
| Miatech Services Ltd | Manufacturing | 2020 |
| Micasesucasa Ltd | Hospitality | 2026 |
| Michael Adamson & Co Limited | Professional & scientific | 2023 |
| Michael Cartwright Photography Ltd | Professional & scientific | 2019 |
| Michael J. Graham (Instrumentation) Limited | Professional & scientific | 1990 |
| Michael Lord Chef Ltd | Hospitality | 2025 |
| Michael Wearmouth Ltd | Professional & scientific | 2023 |
| Mick Harding Ltd | Hospitality | 2024 |
| Mickfeatherstonematerials Ltd | Construction | 2023 |
| Middlefield Farm Limited | Agriculture & fishing | 2025 |
| Middlefield Homes Ltd | Real estate | 2021 |
| Middlers Ltd | Professional & scientific | 2013 |
| Middlesbrough Development Company Limited | Construction | 2019 |
| Middlesbrough Girls FC Limited | Arts & recreation | 2025 |
| Middlesbrough Roller Derby Ltd | Arts & recreation | 2013 |
| Middleton ST George Day Nursery Ltd | Health & social care | 2018 |
| Mike's Tax Emporium Ltd | Professional & scientific | 2019 |
| Milburn EMI Ltd | Professional & scientific | 2025 |
| Milburn Thrive Limited | Education | 2026 |
| Miles Watkins Consulting Ltd | Professional & scientific | 2024 |
| Mill House Tack Shop Limited | Wholesale & retail | 2013 |
| Mill Lane (Norton) Management Company Ltd | Households | 2020 |
| Millennia Engineering Ltd | Wholesale & retail | 2026 |
| Million Likes Ltd | Wholesale & retail | 2019 |
| Million Pugs Ltd | Information & communication | 2019 |
| Mind Clear Ltd | Health & social care | 2019 |
| Mini MOO Publishing Ltd | Information & communication | 2025 |
| Mini Muckshift Limited | Construction | 2005 |
| Minifigs Trading Company Limited | Wholesale & retail | 2025 |
| Minster Court (Durham City) Limited | Professional & scientific | 1991 |
| Mintttw Ltd | Other services | 2025 |
| Mirpur UK Limited | Hospitality | 2023 |
| Misin Group Logistics Ltd | Wholesale & retail | 2025 |
| Miski Coffee Ltd | Hospitality | 2025 |
| Miss Marmalade Clothing Ltd | Wholesale & retail | 2020 |
| Misson Management Services Limited | Professional & scientific | 1992 |
| Mist 101 Ltd | Real estate | 2021 |
| Mitch Financial Ltd | Professional & scientific | 2022 |
| Mitchells Cozy Stoves Ltd | Construction | 2020 |
| Mitchell’S Lifting Limited | Construction | 2022 |
| Mithu Limited | Wholesale & retail | 2019 |
| MJ Hospitality Services Limited | Hospitality | 2020 |
| MJD Business Solutions Ltd | Professional & scientific | 2025 |
| MJF Estates (Stockton) Ltd | Real estate | 2024 |
| MJH & AW Holdings Ltd | Financial services | 2022 |
| MJH Instruments Ltd | Professional & scientific | 2026 |
| MJM Lifting Limited | Construction | 2025 |
| MJN Transport Ltd | Transport & logistics | 2025 |
| MJR Power & Automation Limited | Financial services | 2015 |
| Mjuvs Limited | Administrative & support | 2018 |
| MK EYE Health Ltd | Health & social care | 2026 |
| MK Integrity NDT Ltd | Professional & scientific | 2025 |
| MKE Group Limited | Professional & scientific | 2021 |
| MKY Developments Ltd | Real estate | 2022 |
| ML Funerals Ltd | Other services | 2019 |
| Ml&R Services Limited | Health & social care | 2018 |
| MLD High Voltage Power Services Ltd | Construction | 2025 |
| MLD Properties Ltd | Real estate | 2026 |
| MLD Property Developments (NE) Ltd | Households | 2026 |
| MLG Upholstery Ltd | Other services | 2023 |
| MLJ Teeside Properties Ltd | Real estate | 2024 |
| MLR Coaching Ltd | Education | 2023 |
| MM Civil & Structural Enginnering Ltd | Professional & scientific | 2025 |
| MM Consultancy Services Ltd | Information & communication | 2026 |
| MM Design and Restoration Limited | Other services | 2025 |
| MM Design Direction Ltd. | Administrative & support | 2010 |
| MM Marketing Ltd | Other services | 2024 |
| MMC Specialist Cars Limited | Wholesale & retail | 2004 |
| Mmhd Properties Ltd | Real estate | 2024 |
| MMM Curry Curry Limited | Hospitality | 2015 |
| MMM Housing Ltd | Real estate | 2022 |
| MMS Accountancy Services Limited | Professional & scientific | 2010 |
| MMS Contracting Ltd | Construction | 2026 |
| MMZ Property Ltd | Real estate | 2024 |
| MN Commissioning Services Ltd | Professional & scientific | 2024 |
| Mnmc Investments Ltd | Other services | 2020 |
| MNP (Electrical Services) Limited | Construction | 2002 |
| MNP Services Ltd. | Construction | 2001 |
| MNS Rental Solutions Limited | Real estate | 2025 |
| MO Regency Ltd | Real estate | 2018 |
| MO Wind Services Ltd | Professional & scientific | 2026 |
| Mobile Mechanic 2 U Ltd | Wholesale & retail | 2020 |
| Modd Consulting Limited | Professional & scientific | 2018 |
| Mode Homes Limited | Construction | 2016 |
| Modelbase Limited | Professional & scientific | 2026 |
| Modern Maid Ltd | Administrative & support | 2022 |
| Moderna Surface Design Ltd | Construction | 2019 |
| Modular Engineering Solutions Ltd | Professional & scientific | 2022 |
| MOG Medilogz Limited | Health & social care | 2023 |
| Moja Delivery and Takeaway Ltd | Manufacturing | 2020 |
| Mokase Becke Limited | Professional & scientific | 2014 |
| Momentum Escapes Ltd | Hospitality | 2025 |
| Momos Tula Limited | Wholesale & retail | 2024 |
| Monpizza Ltd | Wholesale & retail | 2025 |