| KJT Properties Ltd | Households | 2016 |
| KK Plant Ltd | Administrative & support | 2025 |
| KLA Electrical Ltd | Construction | 2024 |
| Knife Detection Dogs UK Limited | Other services | 2024 |
| KOB Rentals Limited | Real estate | 2026 |
| Kookaburra Plant Limited | Administrative & support | 2019 |
| KR Rewinds Ltd | Manufacturing | 2018 |
| KS Booze Ltd | Wholesale & retail | 2021 |
| KSR Access Ltd | Professional & scientific | 2021 |
| KUQ E ZI Ltd. | Hospitality | 2017 |
| Kurd Istanbul Barbers Ltd | Other services | 2025 |
| KV Booze Ltd | Wholesale & retail | 2023 |
| KYA Pizza Ltd | Hospitality | 2020 |
| KYK Limited | Wholesale & retail | 2000 |
| L & B Cook Motorsport Ltd | Arts & recreation | 2000 |
| L and C Property Solutions Ltd | Real estate | 2025 |
| L N Gillies Roofing and Cladding Ltd | Construction | 2026 |
| L&G Homes 4 Families Ltd | Real estate | 2025 |
| L&M Limited Limited | Health & social care | 2019 |
| L. D. S. Transport Limited | Information & communication | 1994 |
| LA Royale Aesthetics Limited | Wholesale & retail | 2026 |
| Labour Loop UK Limited | Construction | 2025 |
| Lady Mcbeth Ltd | Health & social care | 2021 |
| Lambton Consultancy and Electrical Services Limited | Professional & scientific | 2017 |
| Lance Foster at Green & White LLP | | 2025 |
| LANDCPROPERTY1 Ltd | Real estate | 2025 |
| Landscaping NE Ltd | Administrative & support | 2023 |
| Landy Pizza Ltd | Hospitality | 2025 |
| Lane Fades Limited | Other services | 2024 |
| Langton Property Partners Ltd | Hospitality | 2025 |
| LANINETY1 Ltd | Construction | 2022 |
| Larron Ltd | Real estate | 2025 |
| Launchpad Homes Limited | Real estate | 2005 |
| Laura Jayne Design NE Ltd | Professional & scientific | 2019 |
| Lawson Properties (NE) Ltd | Real estate | 2025 |
| Layla Attractions Limited | Administrative & support | 2022 |
| Lbfg Barbers Ltd | Other services | 2023 |
| LCC Conveyancing Limited | Professional & scientific | 2025 |
| LE Properties NE Limited | Real estate | 2026 |
| Leamside ALE Company Limited | Hospitality | 2009 |
| Leamside Food Company Limited | Hospitality | 2020 |
| Lean DAD Ltd | Education | 2026 |
| Learnella Limited | Education | 2026 |
| Learning Matters Trust Ltd. | Education | 2011 |
| Lednewky Ltd | Administrative & support | 2012 |
| Lee's Performance Limited | Wholesale & retail | 2023 |
| Leisure Caravans Storage Limited | Transport & logistics | 2016 |
| Lemco Property & Investments Ltd | Financial services | 2023 |
| Lexoral Limited | Information & communication | 2021 |
| LF Aesthetics Clinic Ltd | Health & social care | 2025 |
| LF Joinery & CAD Services Ltd | Construction | 2020 |
| Lg-Tec Limited | Construction | 2019 |
| LGR Studio Ltd | Information & communication | 2026 |
| Lieadaon Ltd | Wholesale & retail | 2018 |
| Lilushika Limited | Real estate | 2025 |
| Lindair Limited | Construction | 2006 |
| Little Windows & Doors Ltd | Wholesale & retail | 2012 |
| Little's Composite Doors Ltd | Manufacturing | 2016 |
| Littlefair Delivery Solutions Ltd | Construction | 2023 |
| Livsplanthouse Ltd | Wholesale & retail | 2025 |
| LJB Ventures Ltd | Professional & scientific | 2022 |
| LLA Roofing and Cladding Ltd | Construction | 2025 |
| LM Renewables Ltd | Manufacturing | 2018 |
| LMC Flooring Ltd | Construction | 2022 |
| Lmss Transport Ltd | Transport & logistics | 2017 |
| Lnhire Ltd | Transport & logistics | 2017 |
| LNO Leisure Ltd | Hospitality | 2025 |
| Loaded & Fired Ltd | Hospitality | 2026 |
| Logistics (Teesside) Limited | Transport & logistics | 2001 |
| Londinium a & C LLP | | 2004 |
| Lovin & Care Ltd | Health & social care | 2025 |
| LPW Steelcraft Limited | Construction | 2021 |
| LSC Accounting Limited | Professional & scientific | 2018 |
| LTM Property Ltd | Real estate | 2025 |
| Luke Fabrication Services Ltd | Construction | 2026 |
| Luke Fabs Ltd | Professional & scientific | 2025 |
| Lullaby North East Ltd | Education | 2024 |
| Luna SOL Shine Ltd | Construction | 2025 |
| Luxury Lens Ltd | Wholesale & retail | 2023 |
| Luxury Lens NE Limited | Wholesale & retail | 2026 |
| Luxury Watch Hire Ltd | Administrative & support | 2024 |
| Lyndhurst Automation Ltd | Manufacturing | 2025 |
| Lynton Court 1960 Limited | Extraterritorial | 2014 |
| Lyons Financial Management 2001 Limited | Professional & scientific | 2023 |
| Lyons Property & Maintenance Services Ltd | Households | 2021 |
| M & G Bell Plumbing (NE) Ltd | Construction | 2023 |
| M & J Electrical Ltd | Construction | 2024 |
| M & T Galley Limited | Construction | 2002 |
| M Collinson Limited | Construction | 2010 |
| M D Contracts NE Ltd | Real estate | 2023 |
| M D Engineering Fluid Power Limited | Administrative & support | 2017 |
| M D Engineering Holdings UK Limited | Education | 2019 |
| M P Inspection Services Limited | Construction | 2011 |
| M R Convenience Store Limited | Wholesale & retail | 2024 |
| M&S Property Services Partnership LLP | | 2022 |
| M.B.C Double Glazing Repairs Ltd | Construction | 2018 |
| Macbro Holdings Limited | Financial services | 2025 |
| Madame Cheap Chic Ltd | Wholesale & retail | 2025 |
| Magic CNC (UK) Ltd | Wholesale & retail | 2021 |
| Magic Welder Ltd | Wholesale & retail | 2026 |