| JJS Leisure Ltd | Hospitality | 2019 |
| JLM NE Properties Ltd | Real estate | 2025 |
| JLT Engineering Services Limited | Construction | 2024 |
| JLT Holdings Limited | Real estate | 2020 |
| JME Performance Limited | Wholesale & retail | 2025 |
| JMP Medical Ltd | Health & social care | 2020 |
| JO Curle Acupuncture Ltd | Administrative & support | 2012 |
| Jones Interior Contracts Limited | Construction | 2003 |
| JQ Properties Ltd | Real estate | 2025 |
| JR Construction & Industrial Ltd | Construction | 2024 |
| Just Sanity Limited | Professional & scientific | 2019 |
| Justright Decorators Limited | Construction | 2025 |
| K&Ktyres Ltd | Wholesale & retail | 2019 |
| K.H. Taylor Limited | Manufacturing | 1972 |
| Kaan Property and Investments Limited | Real estate | 2024 |
| Kanushanth Ltd | Wholesale & retail | 2014 |
| Kayes Tandoori Ltd | Hospitality | 2026 |
| KCL Contracting Ltd | Construction | 2024 |
| KDI Brown Consulting Ltd | Professional & scientific | 2018 |
| KDL Sales Consultants Ltd | Professional & scientific | 2016 |
| Kebab Turk Ltd | Wholesale & retail | 2019 |
| Keith Wilkinson (Electrical Contractors) Limited | Construction | 2002 |
| Keramedics Ltd | Professional & scientific | 2018 |
| Kerrie's Cherubs Childcare Limited | Health & social care | 2020 |
| KEV Dobson Roofing Limited | Construction | 2012 |
| Kevin Hutchings Systems Limited | Construction | 2013 |
| KG Repairs Ltd | Wholesale & retail | 2024 |
| Kids Town Cafe Ltd | Hospitality | 2025 |
| KIN by Mowlem Limited | Wholesale & retail | 2019 |
| Kingsway Garage (Blyth) Limited | Wholesale & retail | 2021 |
| KNP Convenience Store Ltd | Real estate | 2024 |
| Kourtkamilla Jewels Ltd | Health & social care | 2025 |
| Krishna (TW) Limited | Hospitality | 2020 |
| Ktic Developments Limited | Real estate | 2019 |
| Ktic Solutions Limited | Manufacturing | 2017 |
| Kudo Scaffolding Ltd | Construction | 2025 |
| KW Flooring NE Limited | Construction | 2025 |
| L M Financial Management Limited | Financial services | 2015 |
| L Nelson Consulting Limited | Professional & scientific | 2022 |
| L of a Community CIC | Professional & scientific | 2026 |
| L.A Cleanrooms Ltd | Construction | 2024 |
| Laboris Successum Ltd | Arts & recreation | 2019 |
| Lakeshore Global Properties Limited | Real estate | 2025 |
| Lakeshore Management College Ltd | Education | 2026 |
| Landreth Enterprises Ltd | Real estate | 2020 |
| Langley Roofing Services Ltd | Construction | 2023 |
| LAR Electrical Ltd | Construction | 2022 |
| Largrace Ltd | Hospitality | 2025 |
| Lauralogan Ltd | Manufacturing | 2024 |
| Lawson & Thompson Solicitors LLP | | 2015 |
| LBM Group (NE) Ltd | Construction | 2022 |
| LBM Properties (NE) Ltd | Real estate | 2023 |
| Leading-Link | Education | 2011 |
| Leave NO Trace Event Cleaning Ltd | Administrative & support | 2025 |
| LEE Adams Carpet Fitting Services Ltd | Construction | 2013 |
| LEE Madderson Educational Consultancy Ltd | Professional & scientific | 2015 |
| Lets Stay Ltd | Real estate | 2022 |
| LH Renewable Energy Services Ltd | Manufacturing | 2025 |
| Liberty ILS Ltd | Health & social care | 2019 |
| Lidest Limited | Information & communication | 2002 |
| Lifeline Medical Transport Services (Northumberland) Limited | Transport & logistics | 2021 |
| Line of Sight Consultancy Ltd | Administrative & support | 2024 |
| Lines Behind Limited | Arts & recreation | 2019 |
| Lisa Charlton Ltd | Other services | 2014 |
| Little Hubbers by the Sea Limited | Health & social care | 2024 |
| Little Turtle Turns the Tide Ltd | Arts & recreation | 2021 |
| LJD Residential Properties Ltd | Real estate | 2020 |
| LKL Estates Limited | Real estate | 2024 |
| LMJ Farming Ltd | Agriculture & fishing | 2020 |
| Lmjr Services Ltd | Real estate | 2020 |
| LMS Joinery and Building Services Ltd | Construction | 2024 |
| Lmts Facilities Management Services Limited | Other services | 2019 |
| Local Finance Services Limited | Financial services | 2007 |
| Lock and Key Leisure Limited | Real estate | 2024 |
| Lock Security Ltd | Administrative & support | 2026 |
| Lola Cove Films LLP | | 2011 |
| Loud Arts CIC | Arts & recreation | 2007 |
| LS Vehicle Repair Ltd | Wholesale & retail | 2025 |
| LSG Property North East Limited | Real estate | 2026 |
| Lukman Turkish Barber Limited | Other services | 2024 |
| LV Mindwell Prescribing Ltd | Health & social care | 2025 |
| M & C Paving North East Ltd | Construction | 2021 |
| M & M Residential Lettings Limited | Other services | 2002 |
| M a Joinery & Building Ltd | Construction | 2021 |
| M a Joshua Ltd | Wholesale & retail | 2026 |
| M Lynch Bolting and Dismantling Ltd | Professional & scientific | 2025 |
| M&Z(Ne) Limited | Hospitality | 2025 |
| M3 Property Holdings Limited | Real estate | 2024 |
| MAD Fabrication Ltd | Manufacturing | 2025 |
| Magic Scissors Blyth Limited | Other services | 2022 |
| Magpie Property Group Ltd | Real estate | 2025 |
| Magre Enterprise Limited | Water & waste | 2021 |
| Mainteam Fire & Security Limited | Construction | 2011 |
| Management System Solutions Limited | Manufacturing | 2012 |
| Manterneck IT Limited | Information & communication | 2019 |
| Markell Enterprises Limited | Real estate | 2026 |
| Marley Paul Smith Roofing Services Ltd | Construction | 2018 |
| Martin Corner Cloud Solutions Ltd | Professional & scientific | 2018 |
| MB Energy Solutions Ltd | Construction | 2023 |
| MBP Electrical Ltd | Construction | 2021 |