| LOW Waskerley Management Limited | Households | 2001 |
| LRE Holdings Ltd | Households | 2021 |
| LS Carr Electrical Limited | Manufacturing | 2019 |
| Luke a Heffernan Investments Ltd | Financial services | 2025 |
| Lumen Group (North East) Limited | Construction | 2021 |
| Luna Lark Ltd | Manufacturing | 2018 |
| Luxe Automotive Ltd | Wholesale & retail | 2021 |
| Luxe Bricks & Mortar Ltd | Real estate | 2024 |
| Luxe Campers Ltd | Wholesale & retail | 2024 |
| LVV Associates Ltd | Administrative & support | 2016 |
| Lynnhurst Lynton Limited | Professional & scientific | 2023 |
| Lyons Music Supplies Ltd | Wholesale & retail | 2025 |
| Lyredene Management Limited | Professional & scientific | 2025 |
| LYS Psychology Limited | Health & social care | 2026 |
| M J & a Gordon Limited | Wholesale & retail | 2005 |
| M K T Services Ltd | Administrative & support | 2015 |
| M N Ward Ltd | Hospitality | 2025 |
| M Nursey Consulting Ltd | Administrative & support | 2013 |
| M&S Roofing Ltd | Construction | 2023 |
| M.A.D. Flooring Solutions Limited | Construction | 2015 |
| M.D. (NE) Ltd | Real estate | 2014 |
| M.L.C (North East) Limited | Construction | 2025 |
| MAC Properties Ltd | Real estate | 2020 |
| MAC Security and Fire Limited | Construction | 2012 |
| Mack Contracts Ltd | Other services | 2017 |
| Mack Living Limited | Construction | 2024 |
| Mackey Engineering Limited | Administrative & support | 2014 |
| Macs Agri & Commercial Services Limited | Wholesale & retail | 2026 |
| Macs-Couriers Ltd | Transport & logistics | 2026 |
| Mactwo Education Ltd | Education | 2021 |
| Madanai - the Pants People Ltd | Wholesale & retail | 2025 |
| Maddisons Cafe & Bistro Ltd | Hospitality | 2024 |
| Magic Carpets Cleaning Services Ltd | Administrative & support | 2017 |
| Magpie Training Ltd | Administrative & support | 2011 |
| Maid 2 Sparkle C&Hh Limited | Administrative & support | 2025 |
| Maine FM Ltd | Energy | 2025 |
| Maintain Fire and Security Ltd | Construction | 2024 |
| Malsss Ltd | Administrative & support | 2024 |
| Managing Macs Ltd | Wholesale & retail | 2017 |
| Mango (North East) Ltd | Professional & scientific | 2024 |
| Mannat Family Shopper Limited | Wholesale & retail | 2024 |
| Manor Park Limited | Hospitality | 1981 |
| Mansard Properties Ltd | Real estate | 2004 |
| Maritsave Limited | Real estate | 1998 |
| Mark Cant Surveying Ltd | Professional & scientific | 2023 |
| Mark David HR Limited | Professional & scientific | 2009 |
| Mark Emery North East Ltd | Administrative & support | 2013 |
| Mark Harrop Racing (on Course) Limited | Arts & recreation | 2012 |
| Mark Stanley Accountants Limited | Professional & scientific | 2004 |
| Marmitt UK Ltd | Hospitality | 2019 |
| Marvel Digital Trading Ltd | Financial services | 2025 |
| Maskery Property Consultants Limited | Real estate | 2024 |
| Matilda Hope Property Ltd | Real estate | 2022 |
| Matrixlloyd Limited | Professional & scientific | 2009 |
| Matthew Henderson Creative Ideas and Solutions Ltd | Arts & recreation | 2022 |
| Mavsphere Limited | Information & communication | 2026 |
| MBC Renewables Ltd | Professional & scientific | 2022 |
| MC3=E Limited | Manufacturing | 2015 |
| MCN Commercial Repairs Limited | Manufacturing | 2007 |
| Mcnicholas Transport Limited | Transport & logistics | 2019 |
| MD Bookkeeping & Financial Services Ltd | Professional & scientific | 2019 |
| MDM Housing Limited | Real estate | 2022 |
| Mdrs Automotive LRS Limited | Wholesale & retail | 2022 |
| Mdrs Group Holdings Limited | Financial services | 2026 |
| Mdrs Rentals Ltd | Administrative & support | 2022 |
| Mdrs Workshop Limited | Wholesale & retail | 2026 |
| Media Arts Productions Limited | Information & communication | 2026 |
| Media Mayhem Services Limited | Administrative & support | 2016 |
| Mekam Properties Ltd | Real estate | 2025 |
| MER Fleet Services Limited | Professional & scientific | 2014 |
| Merchx Ltd | Wholesale & retail | 2024 |
| Merlin Facilities Limited | Agriculture & fishing | 1993 |
| Mersey Sound Studios Ltd | Extraterritorial | 2026 |
| Meta Holdings Gateshead Ltd | Financial services | 2024 |
| Meta Limited | Construction | 2008 |
| Metal Cloud Limited | Information & communication | 2012 |
| Metro Retail Ltd | Wholesale & retail | 2022 |
| MG Electrical Energy Ltd | Construction | 2025 |
| Miah & Co Accountants Ltd | Professional & scientific | 2023 |
| Micer Ltd | Construction | 2023 |
| Michael James Artworks Limited | Wholesale & retail | 2013 |
| Michael James Joinery (NE) Ltd | Construction | 2021 |
| Michael William Recruitment Limited | Professional & scientific | 2024 |
| Middleheads Limited | Agriculture & fishing | 2012 |
| Middlemast Business Consultants Limited | Information & communication | 2023 |
| Milburn Renwick Joinery Ltd | Construction | 2022 |
| Mill House Consultants Ltd | Professional & scientific | 2018 |
| Millard Food Company Limited | Manufacturing | 2024 |
| Millennium Joinery Ltd | Construction | 2026 |
| Millfab Ltd | Professional & scientific | 2021 |
| Millhouse Developments Limited | Construction | 1985 |
| Millhouse Group Holdings Limited | Financial services | 1990 |
| Millou Training Academy Ltd | Education | 2023 |
| Mine Sure Ltd | Professional & scientific | 2024 |
| Mini-Moon.Co.Uk Limited | Hospitality | 2020 |
| Minjp Ltd | Hospitality | 2024 |
| Minova Services Ltd | Administrative & support | 2016 |
| Minsteracres Retreat Centre | Other services | 2011 |
| Mint Investments Group Ltd | Real estate | 2024 |
| Mirlcan Limited | Professional & scientific | 2015 |