| Lonsdale Eaglescliffe Ltd | Real estate | 2015 |
| Lord Roofing and Grounds Works Ltd | Administrative & support | 2018 |
| LRT Groundworks Ltd | Construction | 2023 |
| Luminar Group Ltd | Financial services | 2025 |
| Luminar Leisure Ltd | Professional & scientific | 2026 |
| M Barnes Trailer Hire Limited | Transport & logistics | 2017 |
| M D Property Solutions Limited | Construction | 2018 |
| M Dixon Interiors Ltd | Construction | 2020 |
| M H Ltd Ferry Hill Ltd | Hospitality | 2026 |
| M K CEE Limited | Professional & scientific | 2020 |
| MA Innovations Ltd | Real estate | 2025 |
| MA Wealth Ltd | Real estate | 2022 |
| Mabec CIC | Education | 2025 |
| Maddie Falcon Ltd | Agriculture & fishing | 2023 |
| Maddison Golf Shop Ltd | Manufacturing | 2022 |
| Madi Construction Management Ltd | Construction | 2024 |
| Magicpd Limited | Information & communication | 2013 |
| Malikon Wholesale Partners Ltd | Wholesale & retail | 2025 |
| Mamta Fast Foods Ltd | Hospitality | 2025 |
| Manor House Ferryhill Ltd | Hospitality | 2019 |
| Marinan Engineering Limited | Professional & scientific | 2007 |
| Marshall Delivery Ltd | Transport & logistics | 2025 |
| Martyn Wallbank Ltd | Professional & scientific | 2015 |
| Marylyn's Unisex Salon Ltd | Other services | 2003 |
| Mattisons Bakery Limited | Manufacturing | 1994 |
| Mcaulay Management Ltd | Professional & scientific | 2019 |
| MDJ Utilities Limited | Construction | 2025 |
| MDT Site Services Ltd | Agriculture & fishing | 2024 |
| ME Electrics Limited | Construction | 2003 |
| Meal Genie Ltd | Administrative & support | 2025 |
| Mel's Travel Ltd | Administrative & support | 2020 |
| Mendaphone (Galashiels) Ltd | Wholesale & retail | 2019 |
| Mendaphone (North East) Ltd | Wholesale & retail | 2022 |
| Mendaphone Ltd | Other services | 2019 |
| Merco (Tyre Management) Ltd | Wholesale & retail | 2006 |
| Middleham Management Company Limited | Administrative & support | 2002 |
| Mill Wood Classic Storage Ltd | Transport & logistics | 2022 |
| Miltop Wealth Ltd | Professional & scientific | 2018 |
| Mineworkings Remediation Specialists Ltd | Construction | 2014 |
| Mint Holdings (North) Limited | Financial services | 2023 |
| Mintpay Ltd | Administrative & support | 2022 |
| Mirror Finish Car Body Repairs Ltd | Wholesale & retail | 2020 |
| MLD Investments (NE) Ltd | Professional & scientific | 2024 |
| MMS Property Limited | Real estate | 2026 |
| Moes Muncher Ltd | Hospitality | 2024 |
| Moos Motors Ltd | Wholesale & retail | 2020 |
| Morgan Solar Ltd | Energy | 2024 |
| Morwick Properties (NE) Ltd | Real estate | 2025 |
| MP Contracting Services Ltd | Financial services | 2015 |
| MP Superior Designs Limited | Construction | 2009 |
| MR Techtrader Ltd | Wholesale & retail | 2025 |
| Munro Project Management Services Limited | Construction | 2014 |
| Mvista Ltd | Professional & scientific | 2010 |
| MWS Heating & Plumbing Limited | Construction | 2013 |
| Nathan Todd Telecoms Ltd | Information & communication | 2023 |
| National Rack Inspections Ltd | Professional & scientific | 2025 |
| Nattrass Logistics Ltd | Transport & logistics | 2025 |
| Nayyarsfoodhouse Ltd | Hospitality | 2025 |
| NDH Engineering Ltd | Manufacturing | 2023 |
| NE Building Services Ltd | Construction | 2021 |
| Neil Harrison Limited | Professional & scientific | 2012 |
| Nella Beauty Limited | Wholesale & retail | 2022 |
| Neovene Limited | Professional & scientific | 2023 |
| Neppem Associates Limited | Administrative & support | 2013 |
| Nesbit Property Ltd | Construction | 2021 |
| Newlands Haulage Ltd | Transport & logistics | 2019 |
| Ngage Racing Limited | Wholesale & retail | 2022 |
| Nick Forbes Consulting by Experience Ltd | Professional & scientific | 2023 |
| Niddry Developments Ltd | Real estate | 2016 |
| Nigel Allan Ltd | Transport & logistics | 2017 |
| Noble Engineering Ltd | Information & communication | 2019 |
| North East Musculoskeletal Society | Other services | 2018 |
| North East Residential Properties Ltd | Real estate | 2004 |
| North East Stairlifts Limited | Administrative & support | 2008 |
| North East Truck & Trailer Limited | Transport & logistics | 2013 |
| Norton Storage Solutions Ltd | Hospitality | 2021 |
| OB Events Craft and Artisan Community Events Limited | Hospitality | 2025 |
| Oldcairn Limited | Information & communication | 2024 |
| OLG Travel Ltd | Administrative & support | 2023 |
| Olivers Tree Services Limited | Agriculture & fishing | 2002 |
| OMT Group Ltd | Wholesale & retail | 2020 |
| ON Point Technologies Ltd | Information & communication | 2019 |
| Oneway Consultancy Ltd | Information & communication | 2024 |
| ORA Life Coaching Ltd | Health & social care | 2025 |
| OTS North East Ltd | Financial services | 2021 |
| Oxbridge Precision Engineers Ltd | Manufacturing | 2001 |
| O’Hare Property Services Limited | Households | 2026 |
| Parker Indian Restaurant Ltd | Hospitality | 2019 |
| Parnaby Holdings Ltd | Real estate | 2023 |
| Parnaby Surfacing & Groundworks Limited | Construction | 2017 |
| PAT Ritchie Associates Ltd | Professional & scientific | 2021 |
| Patcharins Aesthetics Limited | Other services | 2021 |
| PDA Courier Services Ltd | Transport & logistics | 2020 |
| Peer & Cath Co Ltd | Professional & scientific | 2024 |
| Pemspring Limited | Construction | 2013 |
| Perry Williams Ltd | Professional & scientific | 2022 |
| Peter Farish Commercial Sales Ltd | Wholesale & retail | 2023 |
| PHG Holdings Durham Limited | Real estate | 2000 |
| Pivotal Wellbeing Ltd | Information & communication | 2004 |
| Pizza Hot NE Ltd | Hospitality | 2022 |