| Level UP Training Limited | Education | 2023 |
| LHD Automations Limited | Information & communication | 2025 |
| Libaas by Nazish Ltd | Wholesale & retail | 2024 |
| Libertypatt Ltd | Real estate | 2018 |
| Lifestyle Computing Limited | Information & communication | 1999 |
| Lile Properties Ltd | Real estate | 2024 |
| Limetree Analytics Ltd | Information & communication | 2017 |
| Lingobelle Limited | Education | 2026 |
| Linx Business Limited | Professional & scientific | 2018 |
| Lion Birtley Ltd | Hospitality | 2025 |
| Little Acorns OUT of School Club Limited | Health & social care | 2012 |
| Little Palaces Cleaning Services Limited | Administrative & support | 2018 |
| Little Paws Dog Walking Ltd | Other services | 2021 |
| Little WIN Competitions Ltd | Arts & recreation | 2026 |
| Littlelovesbabywear Ltd | Wholesale & retail | 2023 |
| Liulu Limited | Hospitality | 2021 |
| Livefit 14 Ltd | Health & social care | 2023 |
| LJL Services Limited | Professional & scientific | 2018 |
| Ljll Utilities Ltd | Energy | 2017 |
| LJS Industrial Services Ltd | Manufacturing | 2019 |
| LL Candles Ltd | Manufacturing | 2020 |
| Llfa Solutions Ltd | Professional & scientific | 2022 |
| Lltb Limited | Manufacturing | 2024 |
| LMW & SON Investment’S Limited | Real estate | 2021 |
| LNE Road Transport Ltd | Transport & logistics | 2015 |
| Local Glass & Glazing Limited | Construction | 2013 |
| Loch-Glen Associates Ltd | Administrative & support | 2017 |
| Lock & Key Investments Ltd | Real estate | 2022 |
| Lockhaugh Stable Limited | Health & social care | 2016 |
| Longacre Farm Management Company Limited | Professional & scientific | 1999 |
| Lood Developments Ltd | Construction | 2022 |
| Louise Landscapes Limited | Administrative & support | 2021 |
| LOW Fell EA Limited | Real estate | 2019 |
| LOW Investments Limited | Real estate | 2017 |
| Lowes Cleaning Ltd | Administrative & support | 2019 |
| LSH Energy Ltd | Manufacturing | 2023 |
| Luca Construct Limited | Construction | 2025 |
| Lucie Holland Mediation Services Limited | Administrative & support | 2025 |
| Lucy ANN Fitness Ltd | Arts & recreation | 2024 |
| Lumley Snooker & Social Club Limited | Arts & recreation | 2011 |
| Lumsdon Wood Partnership Limited | Professional & scientific | 2009 |
| Lush Locks by Tracy Hollingsworth Ltd | Other services | 2018 |
| LUV Bridal Ltd | Wholesale & retail | 2024 |
| LUX Tanning Salon Ltd | Manufacturing | 2022 |
| LW Developments NE Ltd | Construction | 2024 |
| Lynmar Property Limited | Real estate | 2024 |
| M & G Lumley Ltd | Hospitality | 2023 |
| M a Brooks and Sons Rendering Ltd | Construction | 2023 |
| M B E T Limited | Construction | 2011 |
| M J Harkness & Co Ltd | Professional & scientific | 2016 |
| M J Protective Coatings Limited | Construction | 2016 |
| M Proctor Electrical Limited | Construction | 2014 |
| M R Hvac Solutions Ltd | Construction | 2021 |
| M&D Building & Construction (North East) Ltd | Construction | 2020 |
| M&D Lettings (North East) Ltd | Real estate | 2024 |
| M&D Operations Ltd | Professional & scientific | 2023 |
| M&D Patrick Motor Co. Limited | Wholesale & retail | 2009 |
| M&D Properties (North East) Ltd | Real estate | 2022 |
| M&D Specialist Cleaning Services Ltd | Other services | 2020 |
| M&M Premier Joinery and Building Ltd | Manufacturing | 2020 |
| M&M Property North East Ltd | Real estate | 2024 |
| M.A. Flooring N.E. Ltd | Construction | 2025 |
| M.A.A.D. Limited | Information & communication | 1996 |
| M.R. Cherry Services Limited | Manufacturing | 2009 |
| MA Builders NC Ltd | Construction | 2023 |
| MAC at Baxters Ltd | Hospitality | 2018 |
| Madhouse Media Ltd | Professional & scientific | 2018 |
| Mads and Wils Limited | Financial services | 2024 |
| Mads B Limited | Financial services | 2024 |
| MAG Utilities Limited | Construction | 2022 |
| Magic Cups Ltd | Construction | 2018 |
| Magpie Fashion Limited | Wholesale & retail | 2019 |
| Maine Engineering Limited | Professional & scientific | 2008 |
| Makinen Consulting Ltd | Professional & scientific | 2025 |
| Malayan Ltd | Hospitality | 2024 |
| Malman Technologies Ltd | Manufacturing | 2024 |
| MAM Fleet Solutions Limited | Transport & logistics | 2021 |
| Mane Fella's Limited | Other services | 2025 |
| Mane Tailor Limited | Other services | 2024 |
| Manjot S Limited | Hospitality | 2024 |
| Manorhouse Estates Limited | Real estate | 1999 |
| Marino Foods Partnership LLP | | 2021 |
| Mark Connelly Conservation Ltd | Agriculture & fishing | 2012 |
| Market Momentum Ltd | Wholesale & retail | 2025 |
| Marketplace Estates Limited | Real estate | 2020 |
| Marric Partnership LLP | | 2021 |
| Marshall Murphy Ltd | Real estate | 2019 |
| Marshall's Bathroom Studio Ltd | Construction | 2011 |
| Martin Building Contractors Limited | Construction | 2003 |
| Martin Doherty Limited | Wholesale & retail | 2021 |
| Marvshine Services Ltd | Administrative & support | 2026 |
| Maryculter Foods Partnership LLP | | 2021 |
| Mason Estates NE Limited | Real estate | 2024 |
| Matched Pairs Limited | Wholesale & retail | 1979 |
| Matthew Foods Partnership LLP | | 2021 |
| Matthew IFE Financial Planning Ltd | Professional & scientific | 2025 |
| Maudesville Corp Ltd | Transport & logistics | 2016 |
| MAV Investments Limited | Information & communication | 2011 |
| Mayumi Foods Ltd | Hospitality | 2026 |
| Mbsp Consultancy Limited | Professional & scientific | 2019 |