| Innovo Insights Ltd | Professional & scientific | 2019 |
| Inspacerg Ltd | Manufacturing | 2014 |
| Invest Five Limited | Real estate | 2015 |
| IQ Creative Limited | Professional & scientific | 2024 |
| Ironline Solutions Ltd | Construction | 2025 |
| Ivor Jones (Alnwick) Limited | Construction | 2004 |
| J & K Burgess Property Ltd | Households | 2022 |
| J E Morton Consultancy Limited | Professional & scientific | 2019 |
| J W Bolam Limited | Hospitality | 2018 |
| J.C.B Scaffolding Ltd | Construction | 2024 |
| Jack Douglas Limited | Real estate | 2026 |
| Jack's Furniture Warehouse Ltd | Wholesale & retail | 2024 |
| James Hall & Sons Ltd | Agriculture & fishing | 2012 |
| James Jackson Property Limited | Professional & scientific | 2010 |
| James N. Mclean Limited | Construction | 2002 |
| James R F Armstrong Limited | Arts & recreation | 2021 |
| Jarvy Enterprises Limited | Arts & recreation | 2013 |
| JBD Leisure Limited | Hospitality | 2013 |
| JBM Property Limited | Real estate | 2024 |
| JBT Plumbing & Heating (Alnwick) Ltd | Construction | 2023 |
| JCD Heating Ltd | Construction | 2014 |
| JD Thompson Properties Limited | Real estate | 2021 |
| JDR Skid Steer Services Ltd | Agriculture & fishing | 2020 |
| Jesmond Properties Limited | Real estate | 2024 |
| JET Medicine Limited | Health & social care | 2020 |
| JGC Properties Limited | Real estate | 2021 |
| Jillian Brown Ltd | Real estate | 2024 |
| Jjsk Limited | Hospitality | 2005 |
| Jldrake Ltd | Extraterritorial | 2022 |
| JLL Technical Services Limited | Professional & scientific | 2015 |
| JM Practitioner Limited | Health & social care | 2018 |
| JM9 Investments Ltd | Financial services | 2026 |
| JMN Rope Access Ltd | Professional & scientific | 2014 |
| Jobsons of Alnwick (Warehouse) Limited | Wholesale & retail | 2025 |
| Jobsons of Alnwick Limited | Wholesale & retail | 2020 |
| JOG Storage Solutions Ltd | Construction | 2019 |
| John Fiddes Limited | Agriculture & fishing | 2005 |
| John Francis Planning Ltd | Professional & scientific | 2019 |
| John Gray Limited | Professional & scientific | 2011 |
| John Robson (Painters & Decorators) Ltd | Construction | 2018 |
| John Tanner Ltd | Wholesale & retail | 2026 |
| Jones Fencing Limited | Agriculture & fishing | 2014 |
| Jordan Furness Fencing Ltd | Construction | 2024 |
| JOS. H. Rogers & Company Limited | Households | 1999 |
| JPC Properties (Cramlington) Ltd | Real estate | 2025 |
| JRC Motors Ltd. | Wholesale & retail | 2009 |
| Jubilee Court (Alnwick) Management Company Limited | Households | 2007 |
| K C S Plant Hire Limited | Construction | 2010 |
| KCS (Northeast) Limited | Construction | 2009 |
| Keeping the Balance Limited | Information & communication | 2004 |
| Keir Macleod Ltd | Wholesale & retail | 2022 |
| Kingsley & Coats Ltd | Wholesale & retail | 2022 |
| Kipper Pudding Ltd | Hospitality | 2010 |
| Kitson Trade Windows Limited | Manufacturing | 1997 |
| Kitson Windows Ltd | Manufacturing | 2017 |
| Knights Taxis Limited | Transport & logistics | 2013 |
| Knightsgate Property Soloutions Ltd | Real estate | 2025 |
| Koii 168 Limited | Real estate | 2015 |
| Kore+ Ltd | Other services | 2024 |
| L. Robson & Sons Limited | Manufacturing | 1963 |
| LA Mensa (Rothbury) Limited | Hospitality | 2020 |
| LAL Khazana Ltd | Hospitality | 2015 |
| Lant Medical Ltd | Manufacturing | 2022 |
| Laura Jane Moore Limited | Professional & scientific | 2022 |
| Law Cleans Ltd | Administrative & support | 2025 |
| Layali Investments Ltd | Real estate | 2017 |
| LEE Hope Ltd | Construction | 2020 |
| Lemmington Hall Ltd | Hospitality | 2022 |
| LEO Thai Ltd | Hospitality | 2024 |
| Lesbury Investments Limited | Professional & scientific | 2024 |
| Letton Lodge Management Company Limited | Households | 1984 |
| Lewis C Walker Ltd | Administrative & support | 2021 |
| LHF Land Management Ltd | Real estate | 2026 |
| Lime Kiln Holdings Limited | Extraterritorial | 2017 |
| Lindsey Davidson Limited | Other services | 2022 |
| Linhope Farming Company Limited | Agriculture & fishing | 1991 |
| Linkhouse Farm Limited | Hospitality | 1997 |
| Lionheart Garage Ltd | Wholesale & retail | 2012 |
| Lionheart Radio and Media Community Interest Company | Information & communication | 2007 |
| Lionheart Training Limited | Professional & scientific | 2025 |
| LL (Luxlodge) Ltd | Real estate | 2024 |
| Lochtower Biogas Limited | Energy | 2016 |
| Lockrem Limited | Agriculture & fishing | 2012 |
| Loggerheads Garages Limited | Wholesale & retail | 2008 |
| Longdyke Management Company Ltd. | Households | 2006 |
| Longhoughton Community and Sports Centre Trust | Other services | 2009 |
| Lopata Cleaning Lopata Limited | Wholesale & retail | 2023 |
| Lukasz GOC Ltd | Hospitality | 2025 |
| Luminary Labs Limited | Health & social care | 2022 |
| LVT by Keenwood Limited | Wholesale & retail | 2024 |
| M H George Ltd | Public administration | 2019 |
| M J M Leisure Limited | Real estate | 2003 |
| M Young Flooring Limited | Wholesale & retail | 2022 |
| M&Y Limited | Hospitality | 2018 |
| M.G. Courty (Builder) Ltd. | Administrative & support | 2001 |
| M.J. Douglas Joiner& Builder Ltd | Construction | 2026 |
| Maid Just Right Ltd | Administrative & support | 2023 |
| Maintenance Support Services Ltd | Professional & scientific | 2026 |
| Maison DU Bois Ltd | Manufacturing | 2025 |
| Maison Marie Property Staging Ltd | Professional & scientific | 2025 |