| Orbital Assessments Ltd | Administrative & support | 2018 |
| Orbx UK Limited | Information & communication | 2019 |
| Orchard Blinds (Southsea) Limited | Wholesale & retail | 2001 |
| Orchid Therapy Ltd | Other services | 2016 |
| Orchid Urology Limited | Health & social care | 2015 |
| Ordere UK Limited | Wholesale & retail | 2018 |
| Ordnance Court Management Company Limited | Real estate | 1995 |
| Organisation Cetacea | Professional & scientific | 2010 |
| Oriental Wellbeing Salon Ltd | Health & social care | 2015 |
| Original Talent Recruitment Ltd | Administrative & support | 2018 |
| Origins Global Limited | Real estate | 2025 |
| Orion Property Developments Ltd | Construction | 2021 |
| Orkney Boats Group Limited | Manufacturing | 2020 |
| ORL Limited | Construction | 2019 |
| Orleans Properties Limited | Real estate | 2014 |
| Ormswell Consulting Limited | Professional & scientific | 2025 |
| Ornella Gorza Ltd | Wholesale & retail | 2024 |
| Ortigya Limited | Hospitality | 2022 |
| Osesebaga Limited | Wholesale & retail | 2025 |
| Oska Portsmouth Limited | Wholesale & retail | 2016 |
| Oslond Limited | Wholesale & retail | 2001 |
| Osmaston Villas Limited | Construction | 2019 |
| Ostene Limited | Wholesale & retail | 2001 |
| OT Akpomedaye Ltd | Wholesale & retail | 2023 |
| OTH Properties Limited | Professional & scientific | 2021 |
| Other Green Mango Ltd | Other services | 2015 |
| Other Property Limited | Real estate | 2019 |
| Other Things Art Limited | Manufacturing | 2023 |
| Other World Escapes Ltd | Arts & recreation | 2016 |
| Otie Ltd | Health & social care | 2023 |
| Ototech Ltd | Information & communication | 2023 |
| OUR Zone Limited | Real estate | 2015 |
| OUT of Hours Distribution Limited | Transport & logistics | 2015 |
| Outer Space Genies Ltd | Water & waste | 2026 |
| Outerknown Limited | Wholesale & retail | 2025 |
| Outlook (UK) Limited | Administrative & support | 2000 |
| Outram Limited | Wholesale & retail | 2019 |
| Overdell Developments Limited | Construction | 2024 |
| Ovix Tech Limited | Wholesale & retail | 2026 |
| Owen Aviation Ltd | Manufacturing | 2023 |
| OWL XL CIC | Administrative & support | 2019 |
| Ownspace Ltd | Real estate | 2019 |
| Oxburgh Holdings Ltd | Households | 2024 |
| Oxford Mews Management Company Limited | Households | 1996 |
| Oxhey Village Dairy Ltd | Wholesale & retail | 2013 |
| OY Lasers Ltd | Arts & recreation | 2022 |
| OYO Land Management (Portsmouth) Limited | Real estate | 2005 |
| Oyster Bond Ltd | Health & social care | 2012 |
| Oyster Mews Holdings Limited | Financial services | 2026 |
| Oyster Mews Limited | Households | 2004 |
| Oyster Pearl Limited | Hospitality | 2014 |
| Oyster Quay Management Limited | Households | 1988 |
| Ozon Family Ltd | Wholesale & retail | 2019 |
| P & J Harris Associates Limited | Real estate | 2012 |
| P & P Building and Roofing Contractors Limited | Construction | 2000 |
| P & P Industrial Roofing Ltd | Construction | 2018 |
| P D Hill Roofing Ltd | Construction | 2015 |
| P HB Property Holding Ltd | Real estate | 2026 |
| P J Hopkinson Limited | Professional & scientific | 2013 |
| P K S Plumbing and Heating Services Ltd | Construction | 2020 |
| P L Flooring (Hampshire) Ltd | Construction | 2024 |
| P L H R Bampton Leisure Limited | Arts & recreation | 2020 |
| P L H R Events Limited | Hospitality | 2021 |
| P Powell Brickwork Ltd | Construction | 2015 |
| P R G Contractors Limited | Construction | 2012 |
| P S Welding Services Ltd | Manufacturing | 2008 |
| P Smith Repairs Ltd | Extraterritorial | 2014 |
| P Smith Tiling Services Limited | Construction | 2015 |
| P W Design & Build Limited | Manufacturing | 2010 |
| P&I Management Services Limited | Construction | 2009 |
| P&M Mech Ltd | Real estate | 2019 |
| P&M Wilkin Ltd | Construction | 2026 |
| P&P Building and Roofing Holdings Limited | Financial services | 2025 |
| P. V. Properties (South) Limited | Real estate | 2024 |
| P.D.C. Design and Development Limited | Construction | 2003 |
| P.H Anaesthetic Services Limited | Health & social care | 2016 |
| P.H.B. Industries Limited | Real estate | 1946 |
| P.H.B. Precision Engineering Limited | Manufacturing | 1992 |
| P.L.B Property Services Ltd | Construction | 2025 |
| P.M.C. Construction and Development Services Limited | Construction | 1982 |
| P.U.B. Management Limited | Real estate | 2002 |
| P1 Sports Performance Ltd | Health & social care | 2016 |
| P4 Netpay Ltd | Construction | 2019 |
| PA Contract Sales Limited | Wholesale & retail | 2004 |
| Paanchi Portsmouth Ltd | Hospitality | 2019 |
| PAANCHI2GO Limited | Hospitality | 2025 |
| Pace Services Southern Limited | Construction | 2003 |
| Padely Ltd | Wholesale & retail | 2021 |
| Padova IT Limited | Information & communication | 2007 |
| Page Plastering Ltd | Construction | 2020 |
| Paint & Pinot Ltd | Arts & recreation | 2024 |
| Paint Barn Limited | Other services | 2012 |
| Paintlyne Ltd | Construction | 2019 |
| Pakistan Welfare Association Portsmouth | Other services | 2023 |
| Pal-Pad Limited | Real estate | 2018 |
| Palani Kumar Limited | Administrative & support | 2018 |
| Paleblue Europe Limited | Wholesale & retail | 2012 |
| Palki Flavours Limited | Hospitality | 2026 |
| Pall Europe Limited | Manufacturing | 2010 |
| Pall European Holdings Limited | Professional & scientific | 2013 |