| Mooversuk Ltd | Construction | 2024 |
| MOR Rail Ltd | Construction | 2019 |
| More Than a Run C.I.C. | Health & social care | 2019 |
| Moremon Engineering Ltd | Professional & scientific | 2019 |
| Morgan Angus Inspection Services Ltd | Professional & scientific | 2026 |
| Morgan Painting Ltd | Construction | 2026 |
| Morris-Laverick Developments Limited | Real estate | 2022 |
| Morrison NDT Solutions Ltd | Professional & scientific | 2022 |
| Morrow Electrical Limited | Construction | 2001 |
| MOSSCO75 Ltd | Construction | 2026 |
| MOT Contractor Ltd | Wholesale & retail | 2023 |
| Motherland Gold Foods Ltd | Wholesale & retail | 2026 |
| Motivate Holdings Ltd | Financial services | 2025 |
| Motivate Project Ltd | Education | 2025 |
| Motivate Teesside Limited | Real estate | 2024 |
| Motor Plot Teesside Ltd | Wholesale & retail | 2022 |
| Motorhome Innovations Ltd | Manufacturing | 2024 |
| Mottram Commissioning Limited | Construction | 1995 |
| Mottram Instruments Limited | Professional & scientific | 2018 |
| Mount Farm Developments Ltd | Construction | 2025 |
| Mount Farm Group Ltd | Financial services | 2025 |
| Mountain Sheep Limited | Wholesale & retail | 2017 |
| Mousa's Supermarket Limited | Wholesale & retail | 2025 |
| Mousematco Ltd | Wholesale & retail | 2025 |
| Movek Services Ltd | Administrative & support | 2026 |
| Movira Ltd | Wholesale & retail | 2025 |
| MP HSE Consultancy Ltd | Other services | 2014 |
| MP Plant Assessments Limited | Education | 2021 |
| MP Plant Training Limited | Construction | 2018 |
| Mpft Property Ltd | Construction | 2024 |
| MPI Digital Limited | Manufacturing | 2025 |
| MPI Enterprises Limited | Manufacturing | 2017 |
| MPJ Lifting Solutions Limited | Professional & scientific | 2014 |
| MPK Properties Limited | Wholesale & retail | 2014 |
| MPK Scaffolding Ltd | Construction | 2024 |
| Mpmc (NE) Ltd | Wholesale & retail | 2020 |
| MPW Solutions Ltd | Construction | 2025 |
| MQ Engineering Ltd | Professional & scientific | 2025 |
| MR Cleaning Services Ltd | Administrative & support | 2023 |
| MR M (NE) Limited | Hospitality | 2025 |
| MR M Food Clarendon Ltd | Hospitality | 2026 |
| MR M Food Ltd | Wholesale & retail | 2024 |
| MR MOT Stockton on Tees Ltd | Wholesale & retail | 2026 |
| MR Online Store Ltd | Wholesale & retail | 2026 |
| MR Photobooths Limited | Professional & scientific | 2021 |
| MR Pizza Hartlepool Ltd | Hospitality | 2024 |
| MR Rocca Group Ltd | Wholesale & retail | 2025 |
| MR Shifter Bespoke Removals Limited | Transport & logistics | 2018 |
| MR Shifter Storage (Middlesbrough) Limited | Transport & logistics | 2018 |
| MR Vapes NE Ltd | Wholesale & retail | 2026 |
| MR Wang Takeaway Ltd | Hospitality | 2022 |
| MRB Design Engineering Limited | Professional & scientific | 2026 |
| MRB Structural Design Ltd | Professional & scientific | 2025 |
| MRB Technical Services Limited | Professional & scientific | 2012 |
| MRM Letting Property & Management Ltd | Real estate | 2019 |
| MRR Services Limited | Information & communication | 2025 |
| Mruff Ltd | Construction | 2020 |
| Mrvapour Redcar Ltd | Wholesale & retail | 2025 |
| MS Digital Solutions Ltd | Administrative & support | 2022 |
| MS Race Development Limited | Wholesale & retail | 2017 |
| MS Trade Ltd | Wholesale & retail | 2019 |
| MSB Property Solutions Ltd | Construction | 2025 |
| MSC Offshore Limited | Construction | 2019 |
| MSK Foods ( Stockton) Ltd | Hospitality | 2025 |
| MSK Taxis Ltd | Transport & logistics | 2025 |
| MSM Engineering Solutions Limited | Manufacturing | 2023 |
| MSP Packaging Ltd | Administrative & support | 2025 |
| MSS Access Support Ltd | Professional & scientific | 2025 |
| MSV International Limited | Wholesale & retail | 2004 |
| MSV Sport Limited | Wholesale & retail | 2011 |
| MSV Wholesale Ltd | Wholesale & retail | 2025 |
| MSW Farming Limited | Agriculture & fishing | 2020 |
| MT & J Ltd | Real estate | 2015 |
| MTG Fibre Connections Ltd | Information & communication | 2025 |
| MTH Engineering Ltd | Construction | 2025 |
| MTH Wind Limited | Construction | 2025 |
| MTP GAS Limited | Construction | 2014 |
| Mudgorilla Ltd | Wholesale & retail | 2025 |
| Mugginses Ltd | Wholesale & retail | 2023 |
| Muhommaid Ltd | Wholesale & retail | 2025 |
| Mulberry Yarn Limited | Wholesale & retail | 2010 |
| Multi Media Creative Limited | Professional & scientific | 2014 |
| Multicoat North East Limited | Manufacturing | 2003 |
| Multiploid Ltd | Manufacturing | 2016 |
| Multitrade Services NE Limited | Construction | 2026 |
| Munroe Access Limited | Construction | 2026 |
| Murali Properties Ltd | Real estate | 2024 |
| Murphy Communications Ltd | Information & communication | 2021 |
| Murphy Corporation Limited | Construction | 2018 |
| Murrays RIG Access Limited | Construction | 2019 |
| Murrell & Harland Limited | Real estate | 2024 |
| Musa NE Ltd | Hospitality | 2026 |
| Musaamir Ltd | Wholesale & retail | 2025 |
| Musah Services Ltd | Professional & scientific | 2024 |
| Music Makes ME Ltd | Education | 2017 |
| Musriq Ltd | Professional & scientific | 2019 |
| Musso Developments Ltd | Construction | 2024 |
| Muzdahir Private Limited | Health & social care | 2024 |
| MV Electrical Services Limited | Construction | 2025 |
| MV Event Services Limited | Information & communication | 2025 |