| New Red Dragon Portsmouth Ltd | Hospitality | 2026 |
| New Shanghai Bay Ltd | Hospitality | 2022 |
| New Star Fast Food Ltd | Hospitality | 2020 |
| New Style Turkish Barber Ltd | Other services | 2023 |
| Newbell Homes Ltd | Real estate | 2025 |
| Newlyn House Freehold Ltd | Real estate | 2015 |
| Newman & Seymour Roofing Ltd | Construction | 2025 |
| Newport Plumbing & Heating Limited | Construction | 2002 |
| Nexus Core Ltd | Information & communication | 2025 |
| Nexus Link Ltd | Transport & logistics | 2025 |
| NI HAO Southsea Limited | Hospitality | 2025 |
| Nicholsons Tapas Restaurants Ltd | Hospitality | 2012 |
| Nick Fuller Consultancy Ltd | Professional & scientific | 2025 |
| Nicolet Limited | Financial services | 2025 |
| Nigelsands Car Sales Retail Ltd | Wholesale & retail | 2017 |
| Nikou Letting Ltd | Real estate | 2014 |
| Nixxe Trader Ltd | Wholesale & retail | 2020 |
| NO Name Sauces Ltd | Manufacturing | 2026 |
| NO. 32 Kings Terrace Management Company Limited | Households | 1998 |
| Noah Mapalo Help Centre CIC | Health & social care | 2026 |
| Nomadic Limited | Wholesale & retail | 1998 |
| Noon Instruments Ltd | Information & communication | 2022 |
| Norhampton House Limited | Households | 2019 |
| Norkel Solutions Limited | Professional & scientific | 2023 |
| North West Shop Equipment Limited | | 1973 |
| Northern Endeavours Limited | Professional & scientific | 2022 |
| Norvex Advisory Group Ltd | Professional & scientific | 2026 |
| NOT Just Another Consultancy Ltd | Professional & scientific | 2023 |
| NOT Just Another Group Ltd | Financial services | 2022 |
| Nothing Ventured Vinyl Ltd | Wholesale & retail | 2026 |
| Nouslead Ltd | Information & communication | 2022 |
| Nova Cleanse Ltd | Administrative & support | 2023 |
| Novella Gifts Limited | Wholesale & retail | 2021 |
| NOW Build IT Ltd | Construction | 2018 |
| NOW Prototype IT Limited | Information & communication | 2024 |
| Nu-Era Financial Services Ltd | Financial services | 2015 |
| Number WIZ Ltd | Professional & scientific | 2024 |
| Numedia Technologies Limited | Information & communication | 2008 |
| Nutmeg Lettings Ltd | Real estate | 2025 |
| NX Two Limited | Real estate | 2021 |
| O.I Bar Ltd | Hospitality | 2024 |
| Oakley Gardens Waterlooville Limited | Real estate | 2010 |
| Oakley Residential Investments Limited | Real estate | 2021 |
| Oakley SED Properties Ltd | Real estate | 2024 |
| Oakmount (Ryde) Residents Association Limited | Real estate | 1999 |
| Oakwell Care Ltd | Public administration | 2026 |
| Oakwood Fencing Ltd | Construction | 2019 |
| Oasis of Calm Spa Ltd | Health & social care | 2026 |
| OB Technology Limited | Information & communication | 2024 |
| Obcascades Limited | Hospitality | 2022 |
| Oberon Software Ltd | Information & communication | 2026 |
| Obsouthsea Limited | Hospitality | 2018 |
| OFF Plan MA Ltd | Real estate | 2025 |
| Offbeet (Deli) Limited | Wholesale & retail | 2020 |
| Officialbasariii Ltd | Professional & scientific | 2025 |
| OG Mango Limited | Other services | 2023 |
| Ogle Global Ltd | Agriculture & fishing | 2025 |
| OGO New York Limited | Extraterritorial | 2013 |
| Ohana Holdings Limited | Financial services | 2019 |
| OIL & GAS Academy (UK) Limited | Mining & quarrying | 2007 |
| Old House at Home Management Company Limited | Households | 2005 |
| Oliverball Property Ltd | Real estate | 2020 |
| Olivers Estate Agents Limited | Real estate | 2004 |
| Ollas Food and Services Ltd | Wholesale & retail | 2026 |
| Omega Conception Ltd | Real estate | 2021 |
| Omega Printmakers CIC | Education | 2023 |
| OMO Global Design Ltd | Professional & scientific | 2021 |
| Omoluabi Care Limited | Health & social care | 2023 |
| Omoluabi Holdings Limited | Wholesale & retail | 2023 |
| Omonbhude Global Services Ltd | Health & social care | 2023 |
| On-Point Performance Coaching Ltd | Arts & recreation | 2026 |
| One Body Portsmouth CIC | Other services | 2025 |
| One Gosport Road Limited | Real estate | 2022 |
| One Helena Road Limited | Hospitality | 2016 |
| Only Slightly Drunk Limited | Information & communication | 2021 |
| Onlyhub Ltd | Professional & scientific | 2025 |
| OOH LA LAH Salon Ltd | Other services | 2016 |
| Oomph.Life Holdings Limited | Professional & scientific | 2026 |
| Oomph.Life Investments Limited | Professional & scientific | 2026 |
| Oomph.Life Ltd | Professional & scientific | 2024 |
| Opal Affordable Homes Ltd | Real estate | 2016 |
| Opal Affordable Properties Ltd | Construction | 2025 |
| Opal Coast Ltd | Hospitality | 2020 |
| Operant Labs Limited | Administrative & support | 2022 |
| Optimal Locations Ltd | Real estate | 2024 |
| Optimal Physiotherapy Ltd | Real estate | 2019 |
| Optiorder Ltd | Information & communication | 2026 |
| Oracle Investors Ltd | Real estate | 2023 |
| Orange Door Properties (UK) LLP | | 2017 |
| Orange Door Properties Limited | Real estate | 2017 |
| Organic Professional Ltd | Wholesale & retail | 2017 |
| Orpheus House Ltd | Households | 2019 |
| Osborne Steaks Ltd | Hospitality | 2019 |
| Oscar Charles Associates Limited | Professional & scientific | 2024 |
| Oscarsden Limited | Other services | 2007 |
| OSD Interior Limited | Construction | 2019 |
| OSD Motor Trade Ltd | Wholesale & retail | 2026 |
| Osprey Solent Group Ltd | Professional & scientific | 2023 |
| Osprey Solent Properties Ltd | Real estate | 2024 |
| Osrw Ltd | Administrative & support | 2023 |