| JSD Leisure Limited | Hospitality | 2023 |
| Jsee (NE) Limited | Construction | 2024 |
| JSR Property Services Ltd | Construction | 2020 |
| JTB Trading UK Ltd | Administrative & support | 2025 |
| JTD Development Ltd | Construction | 2025 |
| JTD Rigging Limited | Professional & scientific | 2010 |
| JTH Strategic Consulting Ltd | Professional & scientific | 2026 |
| JTL Group Holdings Limited | Financial services | 2021 |
| JTL Services Holdings Limited | Administrative & support | 2021 |
| JTQ Solutions Ltd | Professional & scientific | 2026 |
| Jules Bespoke Salon Ltd | Other services | 2016 |
| Junction 63 Limited | Real estate | 2025 |
| JWC Utilities Ltd | Construction | 2024 |
| K & K North East Limited | Other services | 2026 |
| K & M Waste Limited | Water & waste | 2021 |
| K K & G (NE) Ltd | Hospitality | 2025 |
| K&A Stays Limited | Real estate | 2025 |
| K&S Homes Ltd | Real estate | 2022 |
| K.Construction Northeast Ltd | Construction | 2026 |
| K2 HSE Consultants Ltd | Professional & scientific | 2012 |
| Kali Savannah Ltd | Arts & recreation | 2019 |
| KAY Homes Northeast Ltd | Construction | 2022 |
| KAY Property Rentals Limited | Real estate | 2025 |
| KC Haulage NE Limited | Transport & logistics | 2025 |
| Kelgan Solutions Ltd | Construction | 2018 |
| Kellet Pipeline Services Limited | Professional & scientific | 2003 |
| Kelly Armstrong JW Ltd | Financial services | 2023 |
| Kelly-Abbott Dance Theatre Limited | Arts & recreation | 2015 |
| Kelz (Harlow Green) Limited | Other services | 2018 |
| KEN Beck Consultancy Ltd | Construction | 2014 |
| Kensington Supply Ltd | Wholesale & retail | 2026 |
| Kepier & Company Limited | Professional & scientific | 2009 |
| Kevin O'Hare Services Ltd | Construction | 2014 |
| KEW Brickwork Ltd | Construction | 2019 |
| Key Fire Ltd | Public administration | 2025 |
| Key Fit Locksmiths Ltd | Other services | 2011 |
| Keyhole Residential Limited | Real estate | 2018 |
| KGR Joinery Ltd | Construction | 2013 |
| Kilo Oscar Ltd | Wholesale & retail | 2017 |
| Kinematronics Ltd | Professional & scientific | 2023 |
| KJD Commercial Property Ltd | Real estate | 2026 |
| KLA Financial Ltd | Administrative & support | 2019 |
| KLB Children’S Therapy Ltd | Health & social care | 2020 |
| KLL Safety Solutions Ltd | Professional & scientific | 2026 |
| KMS Financial Planning Ltd | Professional & scientific | 2008 |
| KMS Wills and Trust's LLP | | 2012 |
| Knaggs & Waggs Ltd | Agriculture & fishing | 2024 |
| Knead to Perform Ltd | Other services | 2025 |
| Kodebaron Ltd | Manufacturing | 2019 |
| Kodiaq Services Limited | Professional & scientific | 2024 |
| Komatsu UK Limited | Manufacturing | 1985 |
| Komatsu UK Pension Trustees Limited | Financial services | 1989 |
| Kosh Ventures Limited | Professional & scientific | 2025 |
| Kozzy Ltd | Wholesale & retail | 2022 |
| Krishna (Birtley) Limited | Hospitality | 2024 |
| KRR Holdings Limited | Financial services | 2021 |
| KRR Project Management Limited | Professional & scientific | 2012 |
| KRR Property Limited | Hospitality | 2020 |
| KT Capital Limited | Construction | 2009 |
| KT Storage (NE) Ltd | Wholesale & retail | 2026 |
| Kumar Investments Ltd | Real estate | 2018 |
| KW Farndell Consulting Ltd | Public administration | 2025 |
| Kymac Ltd | Wholesale & retail | 2009 |
| L & G (NE) Group Limited | Transport & logistics | 2025 |
| L & G Coaches Ltd | Transport & logistics | 2018 |
| L Almeida Ltd | Administrative & support | 2026 |
| L K Y 888 Ltd | Hospitality | 2015 |
| L&G Family Funeral Directors Durham Ltd | Other services | 2024 |
| L.L.T Solution Partners Limited | Professional & scientific | 2018 |
| L.R Tool Hire Ltd | Wholesale & retail | 2023 |
| LA Familia Ben&Sam Drireche Ltd | Hospitality | 2026 |
| LAB Northallerton Limited | Hospitality | 2017 |
| LAB Plumbing & Heating Ltd | Construction | 2025 |
| Labsphere Limited | Information & communication | 2024 |
| Lakunns Limited | Real estate | 2014 |
| LAM Dental Care Limited | Health & social care | 2016 |
| Lambton Rowing Club Ltd | Arts & recreation | 2022 |
| Lambton Secure Logistics Ltd | Transport & logistics | 2024 |
| Lambton Security Holdings Ltd | Information & communication | 2024 |
| Lane Head Development Ltd | Construction | 2018 |
| Lane Traffic Ltd | Construction | 2025 |
| Lantern Red Limited | Hospitality | 2025 |
| Late Life Planning (North) Ltd. | Professional & scientific | 2016 |
| Laverick Hall Farm Property Management Ltd | Households | 2014 |
| Lawson Plant Hire Limited | Administrative & support | 2023 |
| LBA Properties Ltd | Real estate | 2020 |
| LBH Building Supplies Ltd | Wholesale & retail | 2025 |
| LBN Modesty Ltd | Wholesale & retail | 2026 |
| LC Engineering Solutions Ltd | Professional & scientific | 2024 |
| LCS (N.E) Ltd | Construction | 2013 |
| LDS Tech Limited | Professional & scientific | 2017 |
| Lead Solution Management Ltd | Professional & scientific | 2013 |
| Leaf Hair (North East) Limited | Other services | 2010 |
| Leapfrog Homes Estate Agents Ltd | Real estate | 2014 |
| LEC Building & Electrical Contractors Ltd | Construction | 2017 |
| Legacy Leisure Group Ltd | Hospitality | 2024 |
| Leighton Bainbridge Photography Ltd | Professional & scientific | 2026 |
| Leksor Ltd | Construction | 2019 |
| Leon Wood Logistics Ltd | Transport & logistics | 2025 |
| Lets Heat North East Ltd | Other services | 2022 |