| Nphs Mist Sprinkler - UK Ltd | Public administration | 2024 |
| Nphs-Fire Sprinklers Ltd | Construction | 2017 |
| Npif II - Debt NE LP | | 2024 |
| Npif II - Smaller Loans NE LP | | 2024 |
| NRC Pizza Ltd | Hospitality | 2026 |
| NRK Health & Informatics Limited | Health & social care | 2014 |
| NRN Surfacing Limited | Construction | 2025 |
| NRR Property Services Limited | Real estate | 2019 |
| NRS Professional Services Ltd | Administrative & support | 2024 |
| NS Groundworks Ltd | Construction | 2023 |
| NS Health Care & Informatics Private Ltd | Health & social care | 2014 |
| NSA Northeast Ltd | Hospitality | 2022 |
| NSC Techs Ltd | Construction | 2025 |
| Nsew Ltd | Extraterritorial | 2017 |
| Nsgplumbing Ltd | Construction | 2026 |
| NSJ (North East) Limited | Construction | 2017 |
| Nsrg Ltd | Administrative & support | 2016 |
| NSU Investments Ltd | Health & social care | 2017 |
| Ntel Limited | Real estate | 2024 |
| NTG Group Limited | Financial services | 2008 |
| Number Four Market Place Ltd | Real estate | 2024 |
| Numi Scan Gateshead Limited | Health & social care | 2022 |
| NUR Academy Ltd | Education | 2019 |
| Nurtured Care (NE) Limited | Health & social care | 2017 |
| Nurtured Health & Home Care Ltd | Health & social care | 2020 |
| Nuttyslack Solutions Limited | Construction | 2018 |
| Nvacorp Ltd | Information & communication | 2018 |
| Nwachuwu Afican Fancy Shop Ltd | Wholesale & retail | 2026 |
| Nxpower (UK) Limited | Manufacturing | 2005 |
| NXT LVL Fitness Limited | Arts & recreation | 2021 |
| Nédapure Ltd | Wholesale & retail | 2024 |
| O & M Consulting Limited | Hospitality | 2018 |
| O Moldovan Ltd | Health & social care | 2013 |
| O'Donnell Marine Ltd | Arts & recreation | 2025 |
| O'Neill Administrative Services Limited | Administrative & support | 2016 |
| Oak Edge Properties Ltd | Real estate | 2024 |
| Oakdene Homes (North East) Limited | Real estate | 2018 |
| Oakland Development’S N.E. Limited | Construction | 2026 |
| Oakleaf Candles Limited | Extraterritorial | 2002 |
| Oakley (NE) Limited | Construction | 2011 |
| Oakley Bespoke Limited | Manufacturing | 2019 |
| Oakley Stairs Limited | Manufacturing | 2013 |
| Oasis Aquila Community Homes Limited | Real estate | 2016 |
| Oasis Aquila Housing Ltd | Hospitality | 2004 |
| Obateni Limited | Wholesale & retail | 2023 |
| Obichima Global Holdings Ltd | Wholesale & retail | 2026 |
| Obikels Creations Ltd | Manufacturing | 2024 |
| Objective Health Ltd | Health & social care | 2017 |
| OBM Electrical Limited | Construction | 2014 |
| OC Childcare Ltd | Health & social care | 2018 |
| OCD Installations Ltd | Wholesale & retail | 2024 |
| Ocdc Cleaners Limited | Administrative & support | 2018 |
| Ocean Organics Limited | Manufacturing | 1991 |
| Ocean Shores Co. Ltd | Real estate | 2020 |
| Ococo Media Limited | Professional & scientific | 2014 |
| Octo Design Ltd | Professional & scientific | 2001 |
| Odds and Enzos Limited | Transport & logistics | 2024 |
| Odin Energy North East Limited | Construction | 2024 |
| ODO Property Group Ltd | Real estate | 2021 |
| ODO Sports Coaching Limited | Arts & recreation | 2023 |
| Odori Food Limited | Hospitality | 2019 |
| ODS (Bristol) Ltd | Professional & scientific | 2006 |
| Odyssey Locums Ltd | Health & social care | 2008 |
| Oedi's Salon Limited | Other services | 2013 |
| OES Group Ltd | Professional & scientific | 2016 |
| Office Product Solutions Limited | Wholesale & retail | 2007 |
| Offstone Publishing Limited | Extraterritorial | 2010 |
| Ogbako NDI Igbo UK & Ireland Ltd | Other services | 2017 |
| Ogre Studio Ltd | Professional & scientific | 2020 |
| OH Specialist Solutions Limited | Health & social care | 2018 |
| Ohm's Law V=Ir Ltd | Construction | 2015 |
| OIL Spill Products Limited | Wholesale & retail | 2007 |
| Okparamusi Group Ltd | Wholesale & retail | 2025 |
| OKT Company | Professional & scientific | 1963 |
| OLA Accountancy Newcastle Ltd | Professional & scientific | 2026 |
| Olecranon Limited | Health & social care | 2002 |
| Olive Finance Group Ltd | Financial services | 2025 |
| Olive Grove Holdings (NE) Ltd | Real estate | 2024 |
| Olivebell Associates Ltd | Information & communication | 2019 |
| Olivia's Kitchen Ltd | Hospitality | 2019 |
| Olivias World of Adventures CIC | Education | 2026 |
| OLJ Group Ltd | Manufacturing | 2024 |
| Ollerton Management Group Limited | Real estate | 2024 |
| Ollie and Loui Ltd | Hospitality | 2022 |
| Olom Properties Ltd | Real estate | 2021 |
| OM SAI Retail Ltd | Wholesale & retail | 2024 |
| Omega 365 UK Limited | Information & communication | 2004 |
| Omega North East Limited | Manufacturing | 1996 |
| Omega Plastics (Holdings) Limited | Manufacturing | 2024 |
| Omega Plastics Group (Holdings) Limited | Extraterritorial | 2024 |
| Omenegood Limited | Wholesale & retail | 2025 |
| OMG Newcastle Limited | Real estate | 2019 |
| Omoroc Ltd | Wholesale & retail | 2021 |
| OMS Creative Hub Limited | Manufacturing | 2025 |
| ON Point (NE) Ltd | Construction | 2023 |
| ON Top Renovations Ltd | Construction | 2025 |
| ON Tyne Consultancy Ltd | Professional & scientific | 2022 |
| ON Your Feet Events Ltd | Arts & recreation | 2021 |
| One 9 CCR Services UK Ltd | Extraterritorial | 2016 |
| One Carbon World Ltd | Professional & scientific | 2019 |