| Northern Steam Operations Limited | Other services | 2024 |
| Northern Studio Ltd | Professional & scientific | 2016 |
| Northern Tunnelling & Civil Engineering Limited | Construction | 1992 |
| Northlands Roofing Ltd | Construction | 2026 |
| Northolme Properties Limited | Real estate | 2018 |
| Northshore Technical Services Limited | Professional & scientific | 2016 |
| Northstar Accountants Ltd | Professional & scientific | 2025 |
| Northumberland County Developments Ltd | Real estate | 2017 |
| Norton 1 Leases Ltd | Real estate | 2024 |
| Norton 1 Residential Ltd | Real estate | 2023 |
| Norton Bridge & Quality Control Services Limited | Professional & scientific | 2018 |
| Norton Construction Site Services Limited | Construction | 2018 |
| Norton Cosmetic Clinic Limited | Health & social care | 2016 |
| Norton Dragon Limited | Hospitality | 2025 |
| Norton Financial Limited | Professional & scientific | 2021 |
| Norton Grange Trade Cars Ltd | Wholesale & retail | 2021 |
| Norton Green Ltd | Hospitality | 2026 |
| Norton Medicare Limited | Other services | 2019 |
| Norton Nails Ltd | Other services | 2024 |
| Norton Property & Letting Ltd | Real estate | 2026 |
| Norton Road (Stockton on Tees) Management Company Limited | Households | 2007 |
| Norton Road Fish Bar Ltd | Hospitality | 2025 |
| Norton Sports Charity | Arts & recreation | 2010 |
| NOT TRADING10908779 Ltd. | Financial services | 2017 |
| Notit Ltd | Information & communication | 2023 |
| Nova Ministries UK CIC | Other services | 2025 |
| Nova Mundi Limited | Information & communication | 2019 |
| Nova-Star Property Developments Ltd | Households | 2023 |
| Novacore Digital Ltd | Information & communication | 2023 |
| Novidus Solutions Ltd | Transport & logistics | 2026 |
| Novorbis Ltd | Education | 2018 |
| NP Group Holdings Ltd | Financial services | 2026 |
| NR Property Rental Ltd | Real estate | 2024 |
| NRA Engineering Ltd | Professional & scientific | 2023 |
| Nrsd Limited | Wholesale & retail | 2019 |
| NS Power Ltd | Construction | 2026 |
| Nsdes Limited | Professional & scientific | 2013 |
| NST Marine Ltd | Professional & scientific | 2023 |
| Nsuex Limited | Other services | 2015 |
| NT 4 Nails Ltd | Other services | 2025 |
| NT Milburn Limited | Professional & scientific | 2014 |
| NT Sweeting Group Limited | Financial services | 2020 |
| Ntcmm Limited | Wholesale & retail | 2025 |
| Nubrand Ltd | Professional & scientific | 2025 |
| Nugent Plumbing Solutions Ltd | Construction | 2015 |
| Nuin Offshore Ltd | Manufacturing | 2018 |
| NUR Training Academy Ltd | Education | 2026 |
| Nursery Start Limited | Real estate | 2019 |
| Nurturing Nook Childcare Ltd | Health & social care | 2025 |
| Nutmeg and Arlo Limited | Manufacturing | 2017 |
| Nutrition 22 Ltd | Other services | 2024 |
| Nyvera Ltd | Wholesale & retail | 2025 |
| Nzou Freight Limited | Transport & logistics | 2021 |
| O'Brien, Bedford & Clayton Ltd | Construction | 2019 |
| O'Donnells (Aislaby) Ltd | Real estate | 2026 |
| O'Gorman Electrical Limited | Construction | 2019 |
| O.T.E.C.Limited | Agriculture & fishing | 1971 |
| OA Horizon Ltd | Transport & logistics | 2026 |
| Oahkhlance Limited | Hospitality | 2019 |
| Oak House Property Lettings Ltd | Real estate | 2025 |
| Oak Road Motor Factors Limited | Wholesale & retail | 2010 |
| Oakley's Vehicle Repairs Ltd | Wholesale & retail | 2021 |
| Oakmanor Tree & Garden Services Ltd | Administrative & support | 2023 |
| Oakworth Electrical Ltd | Manufacturing | 2020 |
| Oakworth Group Ltd | Professional & scientific | 2024 |
| Oakworth Properties Ltd | Real estate | 2024 |
| Oasis Resources Limited | Agriculture & fishing | 2006 |
| OAT Hill Farm Kennels Ltd | Other services | 2015 |
| OB Systems Limited | Construction | 2018 |
| Obelias International Ltd | Professional & scientific | 2021 |
| Obelisco Media Limited | Professional & scientific | 2024 |
| OBI Studios Ltd | Other services | 2022 |
| Oblique Properties 2 Ltd | Information & communication | 2019 |
| Oblique Properties 3 Ltd | Information & communication | 2019 |
| Ocean Coatings Limited | Professional & scientific | 2015 |
| Ocean Lighting Limited | Wholesale & retail | 2005 |
| Ocean Pavilion Group Ltd | Professional & scientific | 2021 |
| Ochoche Logistics Ltd | Transport & logistics | 2024 |
| Octopus Solutions Group Ltd | Construction | 2023 |
| OD Surveys Ltd | Professional & scientific | 2024 |
| ODD Socks Laundry and Housekeeping Services Ltd | Administrative & support | 2019 |
| OFF the Grid Solutions Ltd | Construction | 2021 |
| Office Capital Supply Limited | Wholesale & retail | 2024 |
| Office Equip Limited | Wholesale & retail | 2025 |
| Offshore Technical Services Ltd | Manufacturing | 2023 |
| Ogelworld Ltd | Construction | 2020 |
| OGW Energy Ltd | Manufacturing | 2026 |
| Ohmyfibre Ltd | Construction | 2022 |
| OIL & GAS Preservation Services Limited | Professional & scientific | 2015 |
| OIM Consultancy Limited | Professional & scientific | 2011 |
| OJM Property Holdings Ltd | Real estate | 2024 |
| Old Mill Rooms Ltd | Hospitality | 2020 |
| Old Thornaby Limited | Hospitality | 2021 |
| OLEG291183 Ltd | Wholesale & retail | 2021 |
| Olegna Solutions Limited | Information & communication | 2025 |
| Oliver Grove Limited | Hospitality | 2025 |
| Olonatural Limited | Wholesale & retail | 2026 |
| Olubola Ltd | Health & social care | 2023 |
| Oluwadare Medical Ventures Ltd | Health & social care | 2022 |
| Olympic Services Ltd | Transport & logistics | 2025 |