| JR Property Maintenance Ltd | Real estate | 2025 |
| JRD Fleet Services Ltd | Wholesale & retail | 2024 |
| JS Medi Clinic Ltd | Health & social care | 2024 |
| JT Wind/Rope Services Ltd | Construction | 2026 |
| Jubilee Stores (Seaham) Limited | Wholesale & retail | 2014 |
| JWC Construction Services Limited | Professional & scientific | 2021 |
| K Hall Properties Ltd | Real estate | 2019 |
| Karisma Holistic and Sound Therapist Ltd | Extraterritorial | 2025 |
| KB Wind Ltd | Manufacturing | 2023 |
| Keal Homes Limited | Real estate | 2018 |
| Keepsakes & Gifts by Alison Ltd | Wholesale & retail | 2022 |
| Kelmec Limited | Manufacturing | 2013 |
| Kenneth M Barrow & Co Limited | Professional & scientific | 2012 |
| Kevin Crabtree Builders Limited | Construction | 2013 |
| Kevs Couriers Limited | Transport & logistics | 2017 |
| Kieder Housing Ltd | Real estate | 2019 |
| KLW Digital Media Ltd | Information & communication | 2026 |
| Kolanot Limited | Information & communication | 2009 |
| Konect Consult Ltd | Professional & scientific | 2022 |
| Konect Tenancy Services (NE) Ltd | Real estate | 2025 |
| Kraftwerx Ltd | Construction | 2016 |
| KS Brickwork NE Ltd | Construction | 2020 |
| KSH (North East) Limited | Construction | 2024 |
| KT Financial Solutions Limited | Professional & scientific | 2006 |
| KWC Engineering Limited | Manufacturing | 2010 |
| L T Thomas Transport Limited | Transport & logistics | 2011 |
| L&S Brickwork North East Ltd | Construction | 2021 |
| L.Brunning Inspection Services Ltd | Construction | 2022 |
| L3 Group Services Ltd | Professional & scientific | 2026 |
| L3 Infra Ltd | Construction | 2024 |
| L3 Optics Ltd | Information & communication | 2016 |
| L3 Property Developments Ltd | Construction | 2024 |
| L3 Resi Ltd | Real estate | 2025 |
| LA Clique Studio Ltd | Other services | 2026 |
| Lady Locks Hair Extensions Ltd | Wholesale & retail | 2013 |
| LAH Fabrication Ltd | Manufacturing | 2021 |
| Langholm Dalton LLP | | 2008 |
| Lascaris Limited | Professional & scientific | 2003 |
| Laura Scribbles Ltd | Professional & scientific | 2023 |
| Lavera Pizza Express Ltd | Hospitality | 2024 |
| Lavera Pizza NE Ltd | Hospitality | 2025 |
| Lavera Pizza Sunderland Ltd | Hospitality | 2018 |
| LC Energize Ltd | Professional & scientific | 2026 |
| LC Recovery Ltd | Transport & logistics | 2017 |
| LCH Renewables Limited | Energy | 2014 |
| Lcham Ltd | Other services | 2024 |
| Legendz Barberz Ltd | Other services | 2023 |
| Leiabu Ltd | Manufacturing | 2025 |
| Leisurespace Limited | Hospitality | 2002 |
| LET IT BEE Bistro Ltd | Hospitality | 2024 |
| Lickety Split Creamery Ltd | Hospitality | 2013 |
| Lighthouse View Holdings Ltd | Professional & scientific | 2022 |
| Linden Fabrication & Engineering Limited | Manufacturing | 1993 |
| Little Waves Day Nursery Limited | Education | 2015 |
| LKB Product Consultancy Ltd | Information & communication | 2025 |
| LM Courier Services Ltd | Transport & logistics | 2020 |
| Local Transport Limited | Transport & logistics | 2003 |
| Londonderry Group Ltd | Hospitality | 2022 |
| Loop-D-Loop Ltd | Wholesale & retail | 2022 |
| Loved by Jacob Limited | Wholesale & retail | 2021 |
| LOW Bros Property Ltd | Real estate | 2024 |
| LOW Carbon Materials Limited | Manufacturing | 2019 |
| LOW Tide Coffee House Ltd | Hospitality | 2026 |
| LR Comms Ltd | Information & communication | 2023 |
| LTG (North East) Limited | Health & social care | 2020 |
| Luke Capital Limited | Real estate | 1991 |
| Luke Homes Ltd | Real estate | 2019 |
| Luke Stays Limited | Real estate | 2019 |
| Luke Wood Holdings Ltd | Real estate | 2025 |
| Lumiere Health Beauty and Aesthetics Ltd | Health & social care | 2025 |
| Lumineux Skin Ltd | Other services | 2025 |
| Lunar Automation Ltd | Professional & scientific | 2023 |
| M English Limited | Construction | 2012 |
| M L Properties Limited | Construction | 2003 |
| M&L Offshore Limited | Mining & quarrying | 2014 |
| M.E. D.P. Limited | Real estate | 2014 |
| Macieira Engineering Limited | Professional & scientific | 2024 |
| Mackwillicious Limited | Hospitality | 2012 |
| Mahakal & Khodiyar Ltd | Wholesale & retail | 2025 |
| Maiden Mother and Crone (Northeast) Ltd | Wholesale & retail | 2026 |
| Maiden, Mother and Crone Ltd | Wholesale & retail | 2025 |
| MAJ Paints 2 Ltd | Wholesale & retail | 2008 |
| Mangat Enterprises 1 Ltd | Hospitality | 2025 |
| Mangatandco Ltd | Hospitality | 2020 |
| Mani Mani Pizza Ltd | Hospitality | 2021 |
| Marine Walk Ltd | Hospitality | 2023 |
| Mark MAW Electrical Ltd | Construction | 2026 |
| Marley Offshore Management Company Limited | Professional & scientific | 2015 |
| Maroon Thunder Limited | Administrative & support | 2017 |
| Maskell Holdings Limited | Financial services | 2026 |
| MB Removal Solutions Ltd | Transport & logistics | 2025 |
| MB Training Services Limited | Construction | 2018 |
| MCM Parcelnet Ltd | Transport & logistics | 2025 |
| MD Improvements Limited | Construction | 2022 |
| Melanie Aesthetics Ltd | Other services | 2022 |
| Melbury Construction Management Ltd | Professional & scientific | 2015 |
| Metcalfe's (NE) Ltd | Construction | 2023 |
| Metro Virtual Assistants Ltd | Administrative & support | 2022 |
| Mhcrar Ltd | Administrative & support | 2024 |
| Mhhcw Ltd | Administrative & support | 2024 |