| KO Build Ltd | Construction | 2021 |
| KO Marketing Ltd | Wholesale & retail | 2024 |
| Kobal Trade Ltd | Wholesale & retail | 2025 |
| Kobe Construction Limited | Construction | 2017 |
| Koda Homes Limited | Real estate | 2025 |
| Kona Clean Teknologies Ltd | Manufacturing | 2025 |
| Kondapi Data Intelligence Ltd | Information & communication | 2024 |
| Koru Mindful Eateries Limited | Hospitality | 2019 |
| Kozi Bathe Ltd | Construction | 2024 |
| Kozo Design Solutions Ltd | Professional & scientific | 2024 |
| KPL Engineering Limited | Other services | 1999 |
| Krispy Kartel @ Shotton Tandoori Ltd | Hospitality | 2026 |
| Krispy Pizza and Grill NE Limited | Hospitality | 2026 |
| Kromas Recruitment Limited | Administrative & support | 2014 |
| Krone Global Consultancy Ltd | Professional & scientific | 2023 |
| KRS Fire Safety Solutions Ltd | Professional & scientific | 2025 |
| Kruzs Ltd | Construction | 2020 |
| KS Management Consultancy Limited | Financial services | 2020 |
| KS Plant Services Ltd | Manufacturing | 2024 |
| KS@ Plant Services Ltd | Construction | 2025 |
| KT & TT Stores Ltd | Wholesale & retail | 2021 |
| KTS Electrical Services Limited | Construction | 2026 |
| KTW Electrical Services Ltd | Construction | 2025 |
| Kudos Accountants Limited | Professional & scientific | 2022 |
| Kudos Commercial Finance Limited | Information & communication | 2017 |
| Kudos Fleet Limited | Wholesale & retail | 2021 |
| Kudos Mortgage Solutions Limited | Financial services | 2022 |
| Kudos Wealth Ltd | Professional & scientific | 2021 |
| Kudos Wealth Management Ltd | Professional & scientific | 2021 |
| Kulekani Limited | Wholesale & retail | 2022 |
| Kurry 251 Limited | Hospitality | 2025 |
| KURTALAN56 Ltd | Other services | 2026 |
| Kustomized Creationz Ltd | Manufacturing | 2024 |
| Kvam Property Management Services Limited | Real estate | 2011 |
| KWM (FP) Ltd | Professional & scientific | 2008 |
| KWM Financial Planning Ltd | Professional & scientific | 2021 |
| KYE Bradley Limited | Real estate | 2022 |
| Kyoyu Management Ltd | Real estate | 2025 |
| L & S a Limited | Professional & scientific | 2011 |
| L a Languages Ltd | Education | 2023 |
| L D H (2010) Limited | Professional & scientific | 2010 |
| L J Hospitality Ltd | Hospitality | 2024 |
| L R Build Ltd | Construction | 2020 |
| L&D Construction Services Limited | Construction | 2020 |
| L&Y International Ltd | Wholesale & retail | 2024 |
| L-Pac Packaging Solutions Ltd | Administrative & support | 2020 |
| L. D. F Fencing & Gardening Services Ltd | Construction | 2022 |
| L.E.R Ridley Ltd | Construction | 2019 |
| L.T. Bar Consultants Limited | Administrative & support | 2019 |
| L.T.'s Greatest Fish & Chip Company Limited | Hospitality | 2019 |
| LA Fibre Ltd | Construction | 2022 |
| LA Piazza Durham Ltd | Hospitality | 2018 |
| Laburnum Housing Ltd | Real estate | 2020 |
| Ladybird Marketing Services Limited | Professional & scientific | 2021 |
| Ladycraft Limited | Construction | 2002 |
| LAF Property Services Limited | Real estate | 2025 |
| LAJ Holdings Ltd | Manufacturing | 2026 |
| Lake Energy Holdings Ltd | Professional & scientific | 2021 |
| Lakeside Motor Company Durham Limited | Wholesale & retail | 2025 |
| Lakeside Team Quest Ltd | Arts & recreation | 2025 |
| Lakx Co. Ltd | Wholesale & retail | 2026 |
| Lambton Groundworks & Civils Ltd | Manufacturing | 2026 |
| Lambton Walk RTM Company Limited | Households | 2006 |
| Lanchester Dairies Limited | Manufacturing | 1994 |
| Lanchester Pizzeria Ltd | Hospitality | 2025 |
| Lanchester Plumbing & Heating Limited | Other services | 2004 |
| Lanchester Property Investments Ltd | Construction | 2013 |
| Lanchester Property Services Ltd | Households | 2019 |
| Lanchester Publications Ltd. | Administrative & support | 2000 |
| Lanchester Timber Company Limited | Real estate | 2012 |
| Landair Commercials Limited | Wholesale & retail | 2018 |
| Laney Hospitality Ltd | Hospitality | 2026 |
| Langley Garden Limited | Hospitality | 2025 |
| Langley Hall Properties Ltd | Real estate | 2022 |
| Langley Lodge Developments Limited | Real estate | 2019 |
| Langley Moor B3 Ltd. | Real estate | 1999 |
| Langley Moor Developments Limited | Real estate | 2007 |
| Langley MOT Centre Ltd | Wholesale & retail | 2024 |
| Langley Park Vets Ltd | Professional & scientific | 2024 |
| Lanox Developments Limited | Arts & recreation | 2015 |
| Lara (North East) Ltd | Hospitality | 2019 |
| Lares Store Ltd | Wholesale & retail | 2025 |
| Lase Cosmetic Limited | Health & social care | 2018 |
| Lase Medical Limited | Health & social care | 2012 |
| Latamco Ltd | Construction | 2023 |
| Latitude Geospatial Ltd | Information & communication | 2020 |
| Launchpad Associate Limited | Administrative & support | 2012 |
| Laverick Archive Ltd | Professional & scientific | 2008 |
| Lawlor Software Ltd | Information & communication | 2000 |
| LAZ Electrical Services Ltd | Construction | 2025 |
| Lazarus Float Therapy Ltd | Other services | 2022 |
| LB Cygnus Media Limited | Professional & scientific | 2006 |
| LB Evil Angel Limited | Professional & scientific | 2007 |
| LBC Civil Engineering Ltd | Construction | 2016 |
| LBI Electrical Ltd | Professional & scientific | 2022 |
| LBJ Civils Ltd | Construction | 2025 |
| Lbox Logistics Ltd | Transport & logistics | 2019 |
| LC Gridworks Ltd | Energy | 2026 |
| LC Renewables Ltd | Construction | 2024 |
| LCJ Limited | Wholesale & retail | 2016 |