| JNR Rail Ltd | Professional & scientific | 2011 |
| JO Raines Consulting Limited | Administrative & support | 2015 |
| Joann FOO Ltd | Information & communication | 2015 |
| John PYE Motors Limited | Wholesale & retail | 2007 |
| John Skidmore & Co Limited | Agriculture & fishing | 2005 |
| Joined-Up Holidays | Other services | 2007 |
| Jonathan Elliott Limited | Construction | 2015 |
| Jonathan Mills Joinery Services Limited | Construction | 2003 |
| JR Heights Limited | Construction | 2025 |
| JR Liquidations Limited | Wholesale & retail | 2025 |
| JR Media Management Ltd | Professional & scientific | 2024 |
| JR Smith Electrical Services Limited | Construction | 2021 |
| JR Smith Property Services Limited | Construction | 2023 |
| JRB Partitions Ltd | Construction | 2022 |
| JRK North East Ltd | Real estate | 2025 |
| JRK Trading Ltd | Real estate | 2026 |
| JS1 Management Limited | Professional & scientific | 2024 |
| JSB Enterprises Limited | Wholesale & retail | 2011 |
| Jsfw Ltd | Real estate | 2023 |
| JT Construction (NE) Ltd | Construction | 2021 |
| JTC Safety & Compliance Ltd | Professional & scientific | 2026 |
| JTS Leisure Limited | Hospitality | 2019 |
| Julie Meighan Therapy Ltd | Health & social care | 2019 |
| Jörd Hospitality Limited | Hospitality | 2025 |
| K & N Brickworks Ltd | Construction | 2015 |
| K C Commercial Finance Limited | Professional & scientific | 1993 |
| K Hewitt Holdings Limited | Construction | 2015 |
| K Jackson Security Services Limited | Administrative & support | 2017 |
| K Minnis Construction Limited | Construction | 2016 |
| K. Hewitt and Co. Limited | Construction | 1983 |
| K.H. PUB Company Limited | Hospitality | 2018 |
| K.M. Properties North West Ltd | Real estate | 2025 |
| K.T. Joinery Limited | Construction | 1999 |
| Kaira Pilates Limited | Arts & recreation | 2025 |
| Kanprees Limited | Wholesale & retail | 2025 |
| Karen Knowles Training and Development Limited | Education | 2013 |
| Karl Tippins Ltd | Information & communication | 2024 |
| Kash&Em MED Ltd | Real estate | 2022 |
| Katam Compliance Services Ltd | Agriculture & fishing | 2023 |
| Katie Leigh Bespoke Limited | Administrative & support | 2024 |
| KAW Therapies Limited | Health & social care | 2006 |
| Kaywood Limited | Professional & scientific | 2017 |
| KB Fabrication & Welding Services Ltd | Manufacturing | 2021 |
| KCC Investments Ltd | Real estate | 2013 |
| Keigh Communications Limited | Professional & scientific | 2013 |
| Kellie COX Wellness Coaching Ltd | Other services | 2022 |
| Kelly Construction Services Ltd | Construction | 2023 |
| Kemp Commercials Limited | Wholesale & retail | 2024 |
| KEN Healthcare Cooperation Limited | Health & social care | 2026 |
| Kenley Holdings Limited | Construction | 2008 |
| Kenley Homes (Etherley Meadows) Limited | Construction | 2025 |
| Kenley Homes Limited | Construction | 2008 |
| Kenny Construction (Durham) Ltd | Construction | 2015 |
| Kenobi Holdings Limited | Administrative & support | 2018 |
| Kevin EDE Groundworks Limited | Construction | 2018 |
| Keystone Roofing & Pointing Ltd | Construction | 2026 |
| KGB Cleaning & Support Services Northern Ltd | Administrative & support | 2017 |
| KH Design Services Limited | Professional & scientific | 2015 |
| Kidzone Durham Limited | Information & communication | 2002 |
| Kinbridge Property Ltd | Real estate | 2026 |
| Kinect Northeast Ltd | Education | 2023 |
| Kingdom Connections Limited | Professional & scientific | 2003 |
| Kingdom Solutions NE Limited | Construction | 2022 |
| Kingsley Meadows (Harrogate) Management Company Limited | Real estate | 2019 |
| Kirby Hill MAN Co Limited | Households | 2019 |
| Kittiwake Homes North East Limited | Real estate | 2023 |
| KJW Financial Planning Ltd | Financial services | 2015 |
| KMJ Smiles Ltd | Health & social care | 2022 |
| Knead a Slice Ltd | Hospitality | 2021 |
| KNL Investment Properties Ltd | Real estate | 2024 |
| Knockemstiff Spirits Limited | Wholesale & retail | 2025 |
| Knox Leisure Limited | Real estate | 2019 |
| Knox Security Services Limited | Professional & scientific | 2014 |
| Kochayantekada Ltd | Hospitality | 2023 |
| Kolor Spray Limited | Construction | 2010 |
| Krafty Giftz Ltd | Wholesale & retail | 2025 |
| Kris Homes Limited | Real estate | 2023 |
| Kura Booth Ltd | Information & communication | 2026 |
| KVH Associate Ltd | Education | 2025 |
| L & E Property Management Limited | Real estate | 2022 |
| L K Cottages Ltd | Hospitality | 2022 |
| L M North East Ltd | Wholesale & retail | 2021 |
| L Steabler Limited | Professional & scientific | 2025 |
| L&L Engineering Group Limited | Professional & scientific | 2026 |
| L.H. (Quarry Plant) Limited | Manufacturing | 1980 |
| L.S.E. Roofing & Cladding Limited | Construction | 2003 |
| Laburnum Consultancy Limited | Professional & scientific | 2024 |
| Lagom Digital Ltd | Professional & scientific | 2025 |
| Lagom Speciality Coffee Ltd | Wholesale & retail | 2024 |
| Lakeside Stables Limited | Agriculture & fishing | 2015 |
| Lakeview Windows Ltd | Construction | 2020 |
| Lamb & Associates Limited | Professional & scientific | 2022 |
| Lancaster Gardens (Phase 2) Management Company Limited | Households | 2023 |
| Lancaster Gardens Management Company Limited | Households | 2020 |
| Lances & Spurs Ltd | Professional & scientific | 2025 |
| Land & Love Ltd | Manufacturing | 2023 |
| Landcoll Investments Ltd | Professional & scientific | 2023 |
| Landcoll Property Developers Ltd | Real estate | 2022 |
| LB Property Management NE Ltd | Real estate | 2024 |
| LBR Joinery Ltd | Manufacturing | 2026 |