| Life Circles Intelligence Ltd | Information & communication | 2026 |
| Lifestyle Darlington North East Limited | Wholesale & retail | 2016 |
| Lifestyle Fitness Clubs Limited | Arts & recreation | 2019 |
| Lifestyle Fitness Group Limited | Arts & recreation | 2019 |
| Lifestyle Fitness Personal Training Limited | Arts & recreation | 2012 |
| Lights UP Holdings Ltd | Arts & recreation | 2023 |
| Lights UP Technical Services Ltd | Arts & recreation | 2022 |
| Liliana Dobre Logistics Limited | Transport & logistics | 2026 |
| Lilli Innovative Cleaning Solutions Limited | Administrative & support | 2003 |
| Lily B'S Bar and Cafe Limited | Hospitality | 2026 |
| Lilysprings Limited | Public administration | 2022 |
| Lilywen Ltd | Hospitality | 2019 |
| Lincoln's Move Ltd | Real estate | 2025 |
| Linda's News Ltd | Wholesale & retail | 2008 |
| Linden Court Owners Limited | Other services | 1980 |
| Linden House Consulting Ltd | Information & communication | 2014 |
| Lineside Fencing NE Ltd | Construction | 2021 |
| Lineside Properties Ltd | Real estate | 2024 |
| Lingfield Education Trust | Education | 2012 |
| LINK2 Recruitment Ltd | Administrative & support | 2019 |
| Linthorpe Developments Limited | Real estate | 2011 |
| Lintoso Ltd | Information & communication | 2026 |
| Linwood Estate Limited | Extraterritorial | 2015 |
| Lion Head Properties Limited | Hospitality | 1995 |
| Lion Head Property Holdings Limited | Real estate | 2026 |
| Lion's DEN Fitness Club Ltd | Arts & recreation | 2024 |
| Lionhouse Consulting Limited | Professional & scientific | 2015 |
| Lionhouse Property Limited | Real estate | 2017 |
| Lionneace Global Relocations Ltd | Real estate | 2025 |
| Liorli Limited | Real estate | 2019 |
| Liquid Holdings Limited | Administrative & support | 2016 |
| Little Bebe’S Day Care Limited | Health & social care | 2025 |
| Little Britaly Ltd | Manufacturing | 2018 |
| Little Lingfields Limited | Health & social care | 2014 |
| Littleton IT Limited | Information & communication | 2013 |
| Live Long & Prosper Ltd | Arts & recreation | 2020 |
| Liviuionitaproperties Ltd | Real estate | 2020 |
| Livium Nrose Ltd | Wholesale & retail | 2025 |
| LJ Shoe Repairs Ltd | Other services | 2012 |
| LJM FAB Ltd | Manufacturing | 2025 |
| LJM PUB Group Chilton Ltd | Hospitality | 2025 |
| LJM PUB Group Ltd | Hospitality | 2025 |
| LJW Distribution Ltd | Wholesale & retail | 2022 |
| LJW Management Ltd | Professional & scientific | 2025 |
| LKA Admin Ltd | Administrative & support | 2024 |
| LKR Wellbeing Limited | Construction | 2014 |
| LM Construction Ltd | Construction | 2023 |
| Lmcl Consultants Ltd | Professional & scientific | 2023 |
| LNF Holdings Ltd | Real estate | 2017 |
| LNF Limited | Wholesale & retail | 2020 |
| LNM Laser Ltd | Manufacturing | 2020 |
| Loanchoice Limited | Financial services | 2012 |
| Lock Tight Wheel NUT Removal Limited | Wholesale & retail | 2024 |
| Lock-Up Properties Limited | Real estate | 1958 |
| Lockley Estates Ltd | Real estate | 2023 |
| Loco Darlington Ltd | Wholesale & retail | 2015 |
| Locomotive Property Sourcing Ltd | Administrative & support | 2026 |
| Locomotive Recruitment and Training Limited | Education | 2024 |
| Locomotive Security Group Ltd | Administrative & support | 2018 |
| Locomotive Skills Centres Limited | Education | 2025 |
| Locum One Limited | Health & social care | 2018 |
| LOD Holdings Ltd | Financial services | 2020 |
| Logic Windows Ltd | Manufacturing | 2021 |
| Lomond Consultancy (NE) Limited | Professional & scientific | 2023 |
| London and North Eastern Railway Company (2013) Limited | Manufacturing | 2013 |
| London House NW Ltd | Real estate | 2025 |
| London Kizomba Festival Ltd | Arts & recreation | 2025 |
| London Reserve Ltd. | Mining & quarrying | 2011 |
| Londontrux Limited | Transport & logistics | 2014 |
| Longfield Trading Limited | Arts & recreation | 2014 |
| Longview Recruitment Limited | Administrative & support | 2025 |
| Look GR8 Ltd. | Wholesale & retail | 2019 |
| Lool Shulan Ltd | Health & social care | 2009 |
| Loop Polymers Ltd | Professional & scientific | 1999 |
| Lord Automotive Darlington Ltd | Wholesale & retail | 2025 |
| Lorimer Electrical Limited | Construction | 2004 |
| Lotties Laser Crafts Ltd | Manufacturing | 2022 |
| Loughheadperformance Ltd | Wholesale & retail | 2025 |
| Louisa LEE Interiors Ltd | Administrative & support | 2017 |
| Louise Carter Aesthetics Limited | Other services | 2026 |
| Louise Marie Jordan Limited | Other services | 2012 |
| Louise Mills Limited | Wholesale & retail | 2025 |
| Louise Mitchell Interiors Ltd | Professional & scientific | 2021 |
| Lovatt Studio Ltd | Professional & scientific | 2020 |
| Love Metal Fabrication Ltd | Manufacturing | 2016 |
| Lovely Laundry NE Ltd | Other services | 2025 |
| Lovesome Holdings Ltd | Real estate | 2025 |
| Lovesome Lettings Limited | Financial services | 2020 |
| LOW Cost Tooling & Developments Ltd | Wholesale & retail | 2011 |
| Lowson Street PRE School Ltd | Health & social care | 2022 |
| Lowther Mini Market Limited | Wholesale & retail | 2017 |
| LR Inspections Ltd | Professional & scientific | 2025 |
| LR Tech Consulting Ltd | Professional & scientific | 2023 |
| LS Advisory Ltd | Information & communication | 2019 |
| LS Property Maintenance Ltd | Manufacturing | 2015 |
| LSB Installations Ltd | Construction | 2013 |
| LSC Darlington Centre Limited | Education | 2026 |
| Lsrry Vjxy Ltd | Wholesale & retail | 2025 |
| LT Access & Maintenance Ltd | Construction | 2025 |
| Lucas Haulage Ltd | Transport & logistics | 2016 |