| North Harbour Allotment Association Limited | Other services | 2025 |
| North Harbour Estate Management Limited | Households | 2011 |
| North Harbour Garage Ltd | Wholesale & retail | 2014 |
| North Security Ltd | Administrative & support | 2023 |
| Northbury Properties Ltd | Real estate | 2020 |
| Northcote Health Services Limited | Health & social care | 2009 |
| Northend Mechanic and Tyres Ltd | Wholesale & retail | 2023 |
| Northpoint Services Limited | Construction | 2022 |
| Northport Construction Services Limited | Construction | 2005 |
| Northshaw Care Recruitment Ltd | Administrative & support | 2020 |
| Northwood (Portsmouth Holdings) Limited | Financial services | 2011 |
| Northwood AJ Property Limited | Real estate | 2019 |
| Northwood Portsmouth Limited | Real estate | 1995 |
| Norton Construction Southern Limited | Construction | 2007 |
| Nosh Events Ltd | Hospitality | 2025 |
| NOT on My Surfaces Limited | Financial services | 2022 |
| NOT Only BUT Also Limited | Information & communication | 2002 |
| Notrace Services Limited | Administrative & support | 1998 |
| Notts Living Ltd | Real estate | 2025 |
| Nova Space Genies Ltd | Wholesale & retail | 2026 |
| Nova Wholesale Ltd | Wholesale & retail | 2025 |
| Novantis Limited | Professional & scientific | 2024 |
| Novari Limited | Arts & recreation | 2012 |
| Novarival UK Ltd | Wholesale & retail | 2025 |
| Novarix Networks Limited | Information & communication | 2026 |
| Novatech Direct Limited | Manufacturing | 2005 |
| Novatech Holdings Limited | Manufacturing | 2009 |
| Novatech Limited | Manufacturing | 1991 |
| Novel Healthcare Ltd | Health & social care | 2023 |
| Novuspace Construction Ltd | Construction | 2021 |
| NOW Invest Limited | Financial services | 2019 |
| NP Healthcare Services Ltd | Administrative & support | 2019 |
| NP Property Development Ltd | Households | 2021 |
| NPG Empowered Ltd | Administrative & support | 2026 |
| Npro Limited | Professional & scientific | 2014 |
| NPS Stores Limited | Wholesale & retail | 2025 |
| NR Advisory Group Ltd | Professional & scientific | 2026 |
| NRG Installations Ltd | Construction | 2008 |
| NRJ Future Ltd | Administrative & support | 2026 |
| NRS Trade PVT Ltd | Hospitality | 2024 |
| NRS Transportation Ltd | Transport & logistics | 2019 |
| NS Solent Ltd | Health & social care | 2022 |
| NSB Decorators Ltd | Construction | 2010 |
| Nsdt Limited | Real estate | 2021 |
| NSF Events Limited | Hospitality | 2024 |
| Nsjs Stores Limited | Wholesale & retail | 2025 |
| NSK Trading and Property Management Limited | Real estate | 2026 |
| NT Analytics Ltd | Information & communication | 2025 |
| NTB Property Management Ltd | Real estate | 2020 |
| NTC Beauty Ltd | Other services | 2019 |
| Nuckley Consulting Ltd | Professional & scientific | 2021 |
| Nugget & Co Jewellery Ltd | Wholesale & retail | 2025 |
| Nulook Solutions Ltd | Construction | 2020 |
| Nurture Them Naturally Ltd | Manufacturing | 2015 |
| NUT Bar Limited | Hospitality | 2022 |
| Nutbourne Developments Limited | Real estate | 2000 |
| Nviro Consulting Ltd | Professional & scientific | 2020 |
| NW Decorating Limited | Construction | 2014 |
| O M Quinn Limited | Health & social care | 2016 |
| O&J Properties Limited | Real estate | 2024 |
| O' Malley Consultant Ltd | Financial services | 2015 |
| O'Briens (Fareham) Limited | Hospitality | 2010 |
| O'Kane Engineering & Fabrication Limited | Manufacturing | 2020 |
| O'Neill Wetsuits Limited | Wholesale & retail | 1999 |
| O'Shea Building & Renovations Ltd | Construction | 2025 |
| O-S-B Consulting Limited | Professional & scientific | 2015 |
| O.A Ventures Ltd | Real estate | 2019 |
| O.C.C Landscape & Construction Ltd | Construction | 2014 |
| OAE Consults Limited | Professional & scientific | 2026 |
| Oak CCL Limited | Administrative & support | 2018 |
| Oak Growth Consultancy Limited | Other services | 2014 |
| Oakdale Fashion Limited | Wholesale & retail | 2025 |
| Oakleaf Electrical Solutions Ltd. | Construction | 2012 |
| Oakley Groundworks Limited | Construction | 2024 |
| Oakley Murphy Limited | Real estate | 1998 |
| Oaksawn Developments Ltd | Construction | 2025 |
| Oakvale Building and Maintenance Ltd | Construction | 2021 |
| Oakwood Estate Planning Limited | Professional & scientific | 2017 |
| Oakworth Furniture Limited | Wholesale & retail | 2008 |
| Oasis Dog Grooming Limited | Other services | 2025 |
| OBS Capital Ltd | Administrative & support | 2026 |
| Ocean GAS Ltd | Construction | 2010 |
| Ocean Ocean Ltd | Health & social care | 2025 |
| Ocean Roofing Ltd | Construction | 2025 |
| Oceanstorm Films (UK) Limited | Information & communication | 2015 |
| Octavian Property Group Limited | Real estate | 2024 |
| Octo Mechanical Engineering Ltd | Construction | 2025 |
| Octocrane Limited | Households | 2015 |
| Oculus Associates Limited | Manufacturing | 1976 |
| Odelane Limited | Professional & scientific | 2025 |
| OE Motor Trader Ltd | Wholesale & retail | 2026 |
| Oegt Ltd | Health & social care | 2017 |
| OEL Nationwide Personnel Limited | Administrative & support | 2024 |
| Office Builders Limited | Construction | 2021 |
| Ofoq Project Management Ltd | Information & communication | 2024 |
| OGP Electrical Solutions Ltd | Construction | 2022 |
| OGR Properties Limited | Construction | 2022 |
| OIL N OIL Ltd | Wholesale & retail | 2025 |
| OJ Painting and Decorating Services Ltd | Construction | 2021 |
| Oj's Discount Ltd | Wholesale & retail | 2003 |