| KC Engineering Bearings Ltd | Manufacturing | 2016 |
| Kconsult Ltd | Professional & scientific | 2020 |
| KDC Rentals Ltd | Real estate | 2025 |
| Keiths' Welding Limited | Manufacturing | 2014 |
| Kelly Hoganson Ltd | Public administration | 2020 |
| Kelly Park Limited | Health & social care | 2001 |
| Kensho Extended School Services LLP | | 2014 |
| Keraco Construction North East Ltd | Construction | 2020 |
| Kewood Ltd | Wholesale & retail | 2025 |
| KH Solve Ltd | Information & communication | 2024 |
| Kitswell Holiday Lettings Limited | Hospitality | 2018 |
| KL Accountants Ltd | Professional & scientific | 2015 |
| KLA Holdings Ltd | Financial services | 2024 |
| Kler's Fish Bar Limited | Hospitality | 2005 |
| KLR Groundwork & Plant Hire Ltd | Construction | 2011 |
| KM Inspection Limited | Professional & scientific | 2020 |
| Kmsol Knowledge Management Solutions Ltd | Information & communication | 2010 |
| Knitsley Mill Leisure Limited | Arts & recreation | 1996 |
| Konstantinos Mantziokas Ltd | Other services | 2019 |
| KPS Manufacturing Limited | Manufacturing | 2024 |
| KPS Models Limited | Wholesale & retail | 2021 |
| Krol Logistics Ltd Ltd | Transport & logistics | 2025 |
| KS Recovery & Transport Ltd | Wholesale & retail | 2024 |
| KTO Lettings Limited | Real estate | 2024 |
| Kudos Inns & Leisure Limited | Hospitality | 1996 |
| Kuki Direct Limited | Professional & scientific | 2026 |
| KV Events Limited | Wholesale & retail | 2024 |
| Kyokushin Karate Club Ltd | Education | 2024 |
| L a Bramwell Services Limited | Administrative & support | 2024 |
| L a M Construction Limited | Construction | 2010 |
| L&M Property North Limited | Real estate | 2024 |
| L.A. Construction & Rentals Ltd | Construction | 2023 |
| L.O T-Coms Ltd | Information & communication | 2021 |
| L19 Services Ltd | Real estate | 2017 |
| LA Fontana Consett Ltd | Hospitality | 2025 |
| Lakey Peak Properties Ltd | Real estate | 2022 |
| LAM Civil Engineering Limited | Construction | 2024 |
| Lamarque Limited | Manufacturing | 2006 |
| Lambert NDT (NE) Limited | Professional & scientific | 2016 |
| Land Connection Ltd | Other services | 2019 |
| Landscape Solutions (North East) Limited | Administrative & support | 2016 |
| Lankco Ltd | Wholesale & retail | 2025 |
| Lateral Humans Limited | Information & communication | 2018 |
| Lauder Landscapes Ltd | Administrative & support | 2020 |
| Lazzari Estates Ltd | Real estate | 2021 |
| LB Cassiopeia Media Limited | Professional & scientific | 2006 |
| LB Cybernet Entertainment Limited | Professional & scientific | 2006 |
| LB Deluxepass Limited | Professional & scientific | 2006 |
| LB Global Web Solutions Limited | Professional & scientific | 2007 |
| LB Grinding Limited | Construction | 2021 |
| LB Ilogic Solutions Limited | Professional & scientific | 2006 |
| LC Access (UK) Limited | Administrative & support | 2023 |
| LC Support Ltd | Administrative & support | 2023 |
| LD Photography Limited | Professional & scientific | 2018 |
| LD Platinum Heating Ltd | Construction | 2018 |
| LDF Electrical Services Ltd | Construction | 2023 |
| LEA Mcconnell Ltd | Arts & recreation | 2023 |
| Leadgate Child Centre Ltd | Education | 2006 |
| Leadgate Tyre Centre Limited | Wholesale & retail | 2018 |
| Leaf Electrical Ltd | Construction | 2024 |
| Learn to Care Ltd | Education | 2020 |
| Leazes Hall Care Home Limited | Health & social care | 2003 |
| Lemon Doors Ltd | Real estate | 2026 |
| Leonard Investments NE Ltd | Real estate | 2021 |
| Lhan Developments Ltd | Real estate | 2025 |
| Lidar Projects Limited | Professional & scientific | 2024 |
| Lifeplan Wills & Trusts Limited | Financial services | 2017 |
| Lifestyle Designs (North East) Limited | Manufacturing | 2019 |
| Liftunion Ltd | Wholesale & retail | 2022 |
| Ligand Chem Limited | Professional & scientific | 2020 |
| Like Minded People Ltd | Administrative & support | 2020 |
| Lime Design (North) Limited | Other services | 2009 |
| Lincoln Legal Ltd | Professional & scientific | 2025 |
| Linen 4 Less Ltd | Extraterritorial | 2012 |
| Lingolearn Ltd | Financial services | 2018 |
| Lingotot (Asia) Ltd | Education | 2020 |
| Lingotot (Europe) Limited | Education | 2019 |
| Lingotot (North America) Limited | Education | 2019 |
| Lingotot (Oceania) Ltd | Education | 2020 |
| Lingotot Derwentside Ltd | Education | 2018 |
| Lingotot Ltd | Education | 2011 |
| Lishman Electrical Services Ltd | Construction | 2015 |
| Lister Recycling & Waste Management Limited | Water & waste | 2015 |
| Little Barn of Calm CIC | Health & social care | 2025 |
| Little BOO Gifts & Invitations Limited | Wholesale & retail | 2016 |
| Little Hearts PRE School Limited | Other services | 2009 |
| Little Italy in Durham Limited | Hospitality | 2022 |
| Little Tipple Bars Company Limited | Hospitality | 2019 |
| Little Topaz LLP | | 2023 |
| Livello Trading Ltd | Administrative & support | 2015 |
| LJD Residential Ltd | Real estate | 2023 |
| LJS Commercials Limited | Construction | 2025 |
| LKM Marketing Solutions Ltd | Information & communication | 2021 |
| Lmecs Holdings Ltd | Financial services | 2024 |
| LMF People Solutions Ltd | Professional & scientific | 2025 |
| Locate Land Ltd | Other services | 2019 |
| Lockey Property Ltd | Real estate | 2022 |
| Lonely Drone Ltd | Professional & scientific | 2022 |
| Love at First Bite Bakery Ltd | Manufacturing | 2024 |
| Love to Stay Limited | Hospitality | 2025 |