| Northumbria Drainage Services Limited | Construction | 2013 |
| Northumbria Home and Garden Ltd | Construction | 2024 |
| Northumbria Homes Limited | Construction | 2017 |
| Northumbria Maritime Services Ltd | Professional & scientific | 2025 |
| Northumbria Print X Distribution Ltd | Administrative & support | 2006 |
| Northumbria Woodworks Limited | Manufacturing | 2010 |
| Northumbrian Design and Development Limited | Construction | 2021 |
| Northumbrian Financial Limited | Financial services | 2004 |
| Northumbrian Holidays Management Services Ltd | Administrative & support | 2023 |
| Northumbrian House to Home Developments Limited | Construction | 2014 |
| Northumbrian Property Developments Limited | Construction | 2004 |
| Northumbrian Property Ltd | Hospitality | 2019 |
| Northumbrian Salmon Supplies Limited | Wholesale & retail | 1986 |
| Nova 11 Estates Ltd | Real estate | 2025 |
| Nova Finance Limited | Wholesale & retail | 1980 |
| NRS Contracting Limited | Construction | 2019 |
| NSB Hospitality Ltd | Hospitality | 2023 |
| NSB Leisure Ltd | Hospitality | 2023 |
| NSK Technical Services Limited | Other services | 2011 |
| NTC Touring Theatre Company Ltd | Arts & recreation | 1979 |
| NU1 Limited | Construction | 2025 |
| Nuziale Bridal Ltd | Wholesale & retail | 2023 |
| O S Field Services Ltd | Professional & scientific | 2022 |
| Oakmont Estate Management Consultants Ltd. | Real estate | 2024 |
| Oasis Battery Solutions UK Ltd | Wholesale & retail | 2023 |
| Obiesoft Limited | Information & communication | 2012 |
| Objectiv Pictures Limited | Information & communication | 2011 |
| Obsidian Project Management Limited | Professional & scientific | 2017 |
| Occupational Safety and Health Consulting Limited | Public administration | 2013 |
| OFF the Grid CIC | Hospitality | 2017 |
| Ogmios Limited | Professional & scientific | 2005 |
| Ohiro Developments Limited | Construction | 2020 |
| OIL and GAS Installations Limited | Manufacturing | 1980 |
| Okra Wellness Salon & Spa Ltd | Extraterritorial | 2016 |
| Old Fashioned Restaurants Limited | Hospitality | 2025 |
| Old Orchard Longframlington Limited | Households | 2004 |
| Oldgate Properties Limited | Real estate | 2019 |
| Oldgate Tavern Limited | Hospitality | 2026 |
| Oldgate Trustees Limited | Professional & scientific | 2018 |
| Olive & Co Food Ltd | Hospitality | 2024 |
| Olive & Co. U.K Ltd | Financial services | 2025 |
| Oliver Plant Services Ltd | Manufacturing | 2020 |
| OMG 666 Limited | Real estate | 2015 |
| Omni Games Ltd | Information & communication | 2021 |
| One HOP North East Limited | Hospitality | 2026 |
| ONEPOINT4 Limited | Professional & scientific | 2008 |
| Onestop Supply Chain Limited | Wholesale & retail | 2010 |
| Onsa Ltd | Arts & recreation | 2019 |
| Ophite Management Ltd | Professional & scientific | 2025 |
| Opteryx Drones Ltd | Manufacturing | 2026 |
| Optimum Scientific Limited | Professional & scientific | 2007 |
| Opto AG Limited | Professional & scientific | 2023 |
| Orange Box Beds Limited | Wholesale & retail | 2017 |
| Orange House Ltd | Real estate | 2020 |
| OS Sales Limited | Wholesale & retail | 2026 |
| Osricks Consulting Limited | Professional & scientific | 2025 |
| Oswin Projects | Health & social care | 2012 |
| Otaris Consulting Ltd | Professional & scientific | 2024 |
| Otter Handmade Ltd | Manufacturing | 2020 |
| OUR Agents Ltd | Real estate | 2022 |
| OUT of Office Coaching Limited | Administrative & support | 2021 |
| P & S Properties Northumberland Ltd | Real estate | 2022 |
| P a Brown & Company Ltd | Professional & scientific | 2001 |
| P C Electrical 2000 Ltd | Construction | 2000 |
| P D Pipe Systems Limited | Construction | 2014 |
| P Evans Ltd | Professional & scientific | 2026 |
| P F Dwyer Limited | Professional & scientific | 2014 |
| P Gibson Engineering Limited | Construction | 2008 |
| P J Cars Ltd | Transport & logistics | 2024 |
| P.A. Lynch Limited | Wholesale & retail | 1962 |
| P.E.C. Furniture Limited | Manufacturing | 1975 |
| PA Joinery & Building Services Limited | Construction | 2024 |
| PA Property Management Limited | Real estate | 2026 |
| Pace Geotechnics Limited | Professional & scientific | 2015 |
| Paddy‘S Morpeth Ltd | Real estate | 2026 |
| Park House Farm Management Company Limited | Real estate | 2016 |
| Parkgrove Paving Ltd | Administrative & support | 2023 |
| Paterson Ltd | Construction | 2023 |
| Paul a Evans Ltd | Construction | 2019 |
| Paul Andison Property Consultant Ltd | Professional & scientific | 2021 |
| Paul Waddington Financial Planning Ltd | Professional & scientific | 2020 |
| Pauna Health Ltd | Health & social care | 2019 |
| Pavilion Entertainment NE Ltd | Hospitality | 2025 |
| Pavilion Tipi Ltd | Hospitality | 2025 |
| PCG Medicolegal Ltd | Health & social care | 2010 |
| Peacock Property Ltd | Real estate | 2024 |
| Peak XV Advisory Services Ltd | Professional & scientific | 2019 |
| Peak XV Property Limited | Real estate | 2022 |
| Pearltek Limited | Professional & scientific | 2002 |
| Pedal Power Cycling Limited | Administrative & support | 2014 |
| Pegswood Community Hub Ltd | Health & social care | 2001 |
| Pegswood Garage Ltd | Wholesale & retail | 2021 |
| Pegswood Pizza Ltd | Hospitality | 2025 |
| Penhill Advisers Limited | Professional & scientific | 2020 |
| Penon Partnership Limited | Professional & scientific | 2003 |
| People Science Consulting Ltd | Professional & scientific | 2019 |
| Perfect PEG Limited | Administrative & support | 2011 |
| Persona Design Ltd | Information & communication | 2022 |
| Pestforce Northumberland Limited | Agriculture & fishing | 2023 |
| Peter Smith Consultancy Services Limited | Construction | 2013 |