| Johnsons Assets (NE) Limited | Administrative & support | 2022 |
| Johnsons Holdings (NE) Limited | Financial services | 2022 |
| JS Batty Decorating Ltd | Construction | 2019 |
| JS Estimating Services Limited | Construction | 2018 |
| JT Home Improvements (NE) Limited | Construction | 2023 |
| Juelston Ltd | Health & social care | 2023 |
| Just the Perfect Gift Ltd | Wholesale & retail | 2024 |
| JWB Engineering Ltd | Professional & scientific | 2025 |
| K. Mcguinness Opticians Ltd | Wholesale & retail | 2024 |
| K9 Pursuits Limited | Other services | 2005 |
| Kadmous Holdings (UK) Limited. | Manufacturing | 1985 |
| KAL (2022) Limited | Professional & scientific | 2019 |
| Karbon Carlton Sadberge LLP | | 2024 |
| Karbon Carlton Staindrop LLP | | 2023 |
| KAS Inns Ltd | Hospitality | 2021 |
| Katell Limited | Manufacturing | 2001 |
| Katiemarieshome Ltd | Professional & scientific | 2025 |
| Kayleigh Atkinson Consultancy Ltd | Health & social care | 2025 |
| KBM Entertainment Ltd | Information & communication | 2024 |
| KC Cable Jointing (NE) Ltd | Manufacturing | 2019 |
| KD Utilities Limited | Energy | 2013 |
| Kennedy Homes Limited | Construction | 2015 |
| Keru Music Ltd | Information & communication | 2026 |
| Ketton Grange Properties Ltd | Wholesale & retail | 2019 |
| Key - Unlocking the Potential Ltd | Professional & scientific | 2009 |
| Key Business Services North East Ltd | Transport & logistics | 2017 |
| Keystone Blue Limited | Professional & scientific | 2017 |
| Keystone Standards Limited | Professional & scientific | 2026 |
| Kindred Living Limited | Wholesale & retail | 2016 |
| Kinetic Holdings Limited | Financial services | 2015 |
| Kiptec Limited | Manufacturing | 2024 |
| Komax Clean Ltd | Administrative & support | 2025 |
| Kotur Limited | Real estate | 2003 |
| KRM Music Ltd | Arts & recreation | 2022 |
| Krscaffolding Limited | Construction | 2026 |
| KS Credit Control Limited | Administrative & support | 2023 |
| Kyleot Cosmetics Ltd | Wholesale & retail | 2025 |
| L&M (NE) Limited | Real estate | 2024 |
| L&T Alderson Limited | Construction | 2019 |
| L1 Properties Ltd | Real estate | 2017 |
| Labels and Print Limited | Manufacturing | 2021 |
| Lacegold Electrical and Mechanical Services Limited | Manufacturing | 1984 |
| Lambert's Ryder Property Ltd | Real estate | 2021 |
| Lamont Leisure Limited | Hospitality | 2008 |
| Laoban Group Ltd | Wholesale & retail | 2025 |
| Lartington Hall Limited | Hospitality | 2011 |
| LASHER3000 Ltd | Other services | 2026 |
| LBE Promotions Limited | Arts & recreation | 2025 |
| LC Properties North East Ltd | Real estate | 2025 |
| Leaff Ltd | Information & communication | 2021 |
| Lean 6 Services Limited | Education | 2019 |
| Learning a New Way CIC | Education | 2022 |
| Lemax NDT Ltd | Energy | 2025 |
| Lepoid Commercial Ltd | Construction | 2025 |
| Lepoid Home Developments Ltd | Real estate | 2022 |
| Lesont UK Ltd | Wholesale & retail | 2024 |
| LG Retail Ltd | Wholesale & retail | 2022 |
| Liam Gibbon Enterprises Ltd | Construction | 2025 |
| Liam Tremain Limited | Construction | 2024 |
| Life Kitchens for Living Limited | Wholesale & retail | 2017 |
| Linoakley (301) Limited | Manufacturing | 1959 |
| LIQUID8 Asset Solutions Ltd | Wholesale & retail | 2018 |
| Liquidity Media Limited | Information & communication | 2024 |
| Liquidity Media Midco Limited | Education | 2022 |
| Liquidity Media Services Limited | Education | 2022 |
| LMD Media Limited | Wholesale & retail | 2026 |
| Loadfix Limited | Other services | 2019 |
| Local Tree and Fencing Specialists Ltd | Administrative & support | 2025 |
| Logic Electrical Ltd | Construction | 2025 |
| Logico Holdings Limited | Financial services | 2021 |
| Logico Logistics Limited | Transport & logistics | 2021 |
| Logico NE Limited | Transport & logistics | 2018 |
| Logico Training Limited | Education | 2021 |
| Longden Doors Holdings Limited | Financial services | 2021 |
| Longden Doors UK Limited | Construction | 2017 |
| Lothian Independent Travel Ltd | Administrative & support | 2023 |
| Lotingo Limited | Administrative & support | 2021 |
| Lowe's Auto Movements Ltd | Transport & logistics | 2025 |
| LOX of Love Leeds Limited | Other services | 2019 |
| LOX of Love Limited | Other services | 2014 |
| LS Williams Comms Ltd | Information & communication | 2025 |
| LT Groundworks (NE) Ltd | Construction | 2022 |
| Ltmg Limited | Information & communication | 2016 |
| LTS Transport Ltd | Transport & logistics | 2024 |
| Lucia Property Portfolio Limited | Real estate | 2021 |
| Lumé Group Limited | Arts & recreation | 2025 |
| M a Smith Limited | Professional & scientific | 2014 |
| M&A Technology Solutions Limited | Administrative & support | 2026 |
| M&H Inspection Ltd | Professional & scientific | 2014 |
| M&P Pro Clean Limited | Administrative & support | 2025 |
| M.H.Inspection Ltd | Construction | 2023 |
| M5TEC Holdings Limited | Financial services | 2018 |
| M5TEC Limited | Professional & scientific | 2014 |
| Macadam School of Dance C.I.C. | Arts & recreation | 2018 |
| Maddison & Rowland Holdings Limited | Financial services | 2023 |
| Maddison Clark Interior Design Ltd | Professional & scientific | 2025 |
| Magnify Consulting Ltd | Professional & scientific | 2022 |
| Majestic Metal Smith Limited | Wholesale & retail | 2025 |
| Malcolm Rand Property Services Limited | Other services | 2010 |
| Maldwyn Associates Limited | Professional & scientific | 2019 |