| Mason Port Properties Ltd | Real estate | 2022 |
| Match Tees Valley CIC | Manufacturing | 2024 |
| Matiya Site Solutions Limited | Professional & scientific | 2025 |
| Maverick Decorators Ltd | Construction | 2021 |
| Mayfair Suite Limited | Hospitality | 2019 |
| Mayfield Insurance Brokers Limited | Financial services | 2017 |
| MBS Property & Investments Ltd | Real estate | 2025 |
| MC Completions Ltd | Construction | 2023 |
| MC Massages Ltd | Health & social care | 2025 |
| MCB Retail Limited | Wholesale & retail | 2020 |
| Mcconnell Roofing Limited | Construction | 2014 |
| Mccullagh Security Consultancy Ltd | Administrative & support | 2018 |
| Mcdonald HSE Consultancy Limited | Professional & scientific | 2013 |
| Mcintosh Structural Design Limited | Professional & scientific | 2012 |
| Mcklean Limited | Real estate | 2019 |
| MCS Construction (NE) Ltd | Construction | 2019 |
| MDC Landscaping Ltd | Construction | 2021 |
| MDC UK Property Ltd. | Real estate | 2021 |
| MDE Installations Ltd | Construction | 2026 |
| MDS (North East) Limited | Professional & scientific | 2019 |
| ME Hopkins Logistics Ltd | Transport & logistics | 2025 |
| Meadow Box Properties Ltd | Real estate | 2023 |
| Meadowcrest Homes Limited | Construction | 2018 |
| Meals on Wheels Hartlepool Community Interest Company | Manufacturing | 2021 |
| Medical Explants Ltd | Transport & logistics | 2019 |
| Medics Lodge Ltd | Wholesale & retail | 2019 |
| Meetas Store Ltd | Wholesale & retail | 2022 |
| Melton Wind Limited | Energy | 2014 |
| MEP Management Services Limited | Professional & scientific | 2020 |
| Mera Technical Services Ltd | Construction | 2024 |
| Mercilord Electrical & Trade Co Ltd | Wholesale & retail | 2025 |
| Meredith Futures Limited | Financial services | 2024 |
| Merlin Food and Beverages Limited | Hospitality | 2023 |
| Merlinpub Ltd | Hospitality | 2019 |
| MET Building Ltd | Construction | 2025 |
| MF Fibre Solutions Ltd | Construction | 2023 |
| Mfibre Ltd | Information & communication | 2022 |
| MG Inns Ltd | Hospitality | 2024 |
| MGC. Agency Limited | Information & communication | 2014 |
| MGT Trading Management Ltd | Households | 2021 |
| Mhgroupuk Ltd | Wholesale & retail | 2026 |
| Michael J D Services Limited | Professional & scientific | 2016 |
| Michael Weeks Ltd | Manufacturing | 2023 |
| Michalski Trans Ltd | Transport & logistics | 2018 |
| Middleton House Ltd | Real estate | 2018 |
| Milano Hpool Limited | Hospitality | 2025 |
| Mill Lane Interiors Limited | Financial services | 2020 |
| Mill Lane Laundrette Ltd | Wholesale & retail | 2009 |
| Millers Services Ltd | Construction | 2026 |
| Milliways Studio Limited | Professional & scientific | 2026 |
| Mills Family Group Holding Ltd | Financial services | 2023 |
| Millston Postcards Ltd | Professional & scientific | 2009 |
| Milo Flower Limited | Wholesale & retail | 2025 |
| Milu Technologies Limited | Information & communication | 2026 |
| Milu Technology Limited | Information & communication | 2016 |
| Mims Editorial CIC | Professional & scientific | 2026 |
| Minch Offshore Services Limited | Construction | 2017 |
| Minhstry Ltd | Information & communication | 2020 |
| Minkon Ltd. | Manufacturing | 1982 |
| Miramar Staindrop Limited | Real estate | 2025 |
| MJ Structures Ltd | Construction | 2006 |
| Mjbinspectionservices Ltd | Other services | 2016 |
| MJC Material Solutions Ltd | Construction | 2026 |
| MJC Mechanical Services Ltd | Construction | 2024 |
| MJD Contractors Ltd | Construction | 2024 |
| MJE Technical Services Limited | Construction | 2012 |
| MJG E&I Services Ltd | Construction | 2025 |
| MJR Commercial Consultants Ltd | Professional & scientific | 2016 |
| Mjss Ltd | Administrative & support | 2026 |
| MK Joinery and Building Limited | Construction | 2023 |
| MK Wilson Roofing Limited | Construction | 2019 |
| MKE Chauffeurs Ltd | Transport & logistics | 2016 |
| MKP Transport Limited | Administrative & support | 2020 |
| Mksjs Properties Limited | Real estate | 2024 |
| MKT Property Services Ltd | Real estate | 2025 |
| MLI Electrical Ltd | Mining & quarrying | 2015 |
| MLS1 Logistics Ltd | Transport & logistics | 2022 |
| MM Carlill House Limited | Hospitality | 2021 |
| MM Investments NE Ltd | Financial services | 2025 |
| MMM Fast Foods Ltd | Hospitality | 2023 |
| MN Qhsse Services Limited | Construction | 2019 |
| MO & Sons (NE) Ltd | Other services | 2025 |
| Modified Detailing & Customs Limited | Administrative & support | 2025 |
| Moflol Limited | Real estate | 2025 |
| Mohan Instrumentation Services Limited | Professional & scientific | 2013 |
| Mohan Property Ltd | Real estate | 2025 |
| Molly Minton Ltd | Administrative & support | 2023 |
| Monk MD Ltd | Real estate | 2021 |
| Monkey Hangers Ltd | Construction | 2025 |
| Monster Stunt and Firework Shows Ltd | Arts & recreation | 2009 |
| Monsur Enterprise Limited | Administrative & support | 2016 |
| Montana Pizza Hartlepool Ltd | Hospitality | 2024 |
| Moondowner Holdings UK Ltd | Professional & scientific | 2012 |
| Morepour North Limited | Other services | 2017 |
| Morgan Associates Facilities Management Ltd | Administrative & support | 2014 |
| Morley Park Limited | Financial services | 2025 |
| Morphill Interiors Ltd | Manufacturing | 2026 |
| Morphill Properties Ltd | Real estate | 2024 |
| Morphill Services Ltd | Manufacturing | 2024 |
| Morrison Solutions (North) Limited | Construction | 2025 |