| Meadow Croft Developments Ltd | Construction | 2025 |
| Mean Green Promotions Ltd | Administrative & support | 2026 |
| Meat Business Women Ltd | Administrative & support | 2019 |
| Mech-Tool Engineering Limited | Manufacturing | 2000 |
| Mech-Tool Holdings Limited | Professional & scientific | 2014 |
| Mech-Tool Investments Ltd | Real estate | 2013 |
| Mech-Tool Limited | Extraterritorial | 2023 |
| Mech-Tool Ventures Limited | Professional & scientific | 2014 |
| Media Creative Limited | Information & communication | 2007 |
| Mediavantage Limited | Professional & scientific | 2012 |
| Medic 4U Ltd | Education | 2024 |
| Medical Services Northern Limited | Health & social care | 2011 |
| Mediwell Services Ltd | Administrative & support | 2025 |
| Medrano Haste Ltd | Information & communication | 2017 |
| Medtec Consulting Limited | Professional & scientific | 2011 |
| MEE & BEE Ltd | Manufacturing | 2020 |
| Meera JO Ltd | Wholesale & retail | 2025 |
| Meet N Marrow Ltd | Hospitality | 2025 |
| Mel's Sandwich Vans Limited | Hospitality | 2024 |
| MEM Motors Ltd | Wholesale & retail | 2012 |
| Mendes Management Ltd | Arts & recreation | 2017 |
| Mercia Court Residents Management Company Limited | Households | 1988 |
| Mercury Asset Finance Limited | Administrative & support | 2010 |
| Mercury International Solutions Limited | Professional & scientific | 2009 |
| Mercury Metals London Limited | Wholesale & retail | 2010 |
| Mercy TEE Ltd | Hospitality | 2025 |
| Meribel 85 Ltd | Real estate | 2023 |
| Merriam Engineering & Design Limited | Professional & scientific | 2016 |
| Merriam Investments Limited | Real estate | 2022 |
| Merry Concepts Limited | Administrative & support | 2026 |
| Merrybent Imports Ltd | Wholesale & retail | 2023 |
| Merrybent Project Management Ltd. | Construction | 2004 |
| Metal Dog Limited | Extraterritorial | 2025 |
| Metarave Limited | Information & communication | 2024 |
| Metcalfe Water Services Ltd | Administrative & support | 2019 |
| Method Property Ltd | Real estate | 2020 |
| Metro Ceramics Limited | Construction | 2006 |
| Metro Furniture North East Ltd | Manufacturing | 2017 |
| Meze Multimedia Ltd | Professional & scientific | 2022 |
| MGB Signalling Limited | Construction | 2003 |
| Mgfa Future Pathways Ltd | Education | 2020 |
| MGH Property Maintenance Ltd | Construction | 2023 |
| MGI Properties (North East) Limited | Real estate | 2017 |
| MHH Salons Limited | Other services | 2026 |
| MHP (Darlington) Limited | Other services | 2025 |
| MHW Services Ltd | Professional & scientific | 2025 |
| MHZ Logistics Ltd | Transport & logistics | 2025 |
| Miah Hickerson Ltd | Hospitality | 2026 |
| Miao Sheng Kitchen Ltd | Hospitality | 2025 |
| Michael James Holdings Ltd | Real estate | 2025 |
| Michael James Partnership LLP | | 2025 |
| Michael John Limited | Wholesale & retail | 2025 |
| Michael Martin Car Sales Limited | Wholesale & retail | 2010 |
| Michael Walker Ltd | Education | 2023 |
| Michaelam Limited | Wholesale & retail | 2026 |
| Michaels Jewellers Limited | Wholesale & retail | 2015 |
| Michal Delkowski Ltd | Transport & logistics | 2018 |
| Mick and Daughters Limited | Wholesale & retail | 2026 |
| Middle East Holding Limited | Construction | 1893 |
| Middle Oak Management Limited | Other services | 1993 |
| Middlesbrough Powder Coating Ltd | Manufacturing | 2024 |
| Middlestone Homes Ltd | Construction | 2021 |
| Middleton Chef Limited | Hospitality | 2023 |
| Middleton Coal Limited | Mining & quarrying | 2018 |
| Middleton GEM Properties Ltd | Real estate | 2018 |
| Middleton Hall Limited | Hospitality | 1900 |
| Middleton Hall Retirement Village Trustees Limited | Administrative & support | 2019 |
| Midland Hand Clinic Limited | Health & social care | 2016 |
| Midland Plumbing Supplies Ltd | Construction | 2019 |
| Midnight Business Limited | Information & communication | 2016 |
| Midtown Properties Ltd | Real estate | 2020 |
| Miiko Solutions Ltd | Information & communication | 2019 |
| Mijorugra Limited | Transport & logistics | 2017 |
| Mikaela Wright's Marketing & Service Limited | Other services | 2019 |
| Mike Boddy Limited | Energy | 2021 |
| Mike Guest Facilities Management Mgfm Limited | Professional & scientific | 2018 |
| Mike Matthews Business Consulting Limited | Professional & scientific | 2019 |
| Mike Thorne and Associates Limited | Professional & scientific | 2001 |
| Mikjoe Ventures Limited | Information & communication | 2025 |
| Mikussowa Trans Ltd | Transport & logistics | 2018 |
| Milan-Ghinea Ltd | Transport & logistics | 2025 |
| Mill Consulting Limited | Professional & scientific | 2026 |
| Mill Lock Investments Ltd | Construction | 2021 |
| Millennial Market 23 Ltd | Wholesale & retail | 2020 |
| Millennium Legal Limited | Administrative & support | 2023 |
| Miller Finserv Ltd | Financial services | 2025 |
| Miller Law (U.K.) Ltd | Professional & scientific | 2021 |
| Miller Properties & Real Estate Ltd | Real estate | 2018 |
| Miller Property (North) Limited | Real estate | 2022 |
| Millerspropertysearch Ltd | Real estate | 2023 |
| Millman Enterprises (UK) Ltd | Wholesale & retail | 2020 |
| Mills Lettings Limited | Real estate | 2019 |
| Millward Holdings Group Ltd | Financial services | 2024 |
| Minara Estates Limited | Real estate | 2024 |
| Mind Body Balance Ltd | Health & social care | 2015 |
| Minerva Growth (North East) | Financial services | 2024 |
| Ming Chef (TS) Ltd | Hospitality | 2018 |
| Minibakes Ltd | Manufacturing | 2025 |
| Minimental Limited | Wholesale & retail | 2024 |
| Minimix (Northeast) Limited | Construction | 2000 |