| Onsite Crane & Commercial Limited | Construction | 2003 |
| Oodachee Ltd | Professional & scientific | 2018 |
| Ooivie Ltd | Wholesale & retail | 2024 |
| Open Bridging Limited | Financial services | 2025 |
| Open Hairdressing Berkhamsted Limited | Administrative & support | 2017 |
| Open Hairdressing LKR Limited | Administrative & support | 2025 |
| Open Hairdressing Tring Ltd | Other services | 2025 |
| Open Loans Limited | Financial services | 2025 |
| Opta Consulting Limited | Information & communication | 2005 |
| Optima Europe Limited | Professional & scientific | 2003 |
| Optimize Growth Ltd | Professional & scientific | 2024 |
| Opus Nebula Limited | Information & communication | 2014 |
| Orange Monkey Recruitment Ltd | Administrative & support | 2022 |
| ORB Sustainability Consulting Ltd | Professional & scientific | 2019 |
| Ormondroyd Legal Consulting Limited | Professional & scientific | 2026 |
| Oscailte Ltd | Information & communication | 2020 |
| Oscar Haulage Ltd | Transport & logistics | 2025 |
| Osco Group Limited | Real estate | 2023 |
| Osteo Inc Limited | Other services | 2024 |
| Oven Genie Ltd | Administrative & support | 2026 |
| OX Construction Recruitment Limited | Administrative & support | 2024 |
| P a Pool Limited | Administrative & support | 2006 |
| P B Sutton Engineering Limited | Professional & scientific | 2011 |
| P.H.D Recruitment Limited | Administrative & support | 2025 |
| P.J. Watson Limited | Wholesale & retail | 1966 |
| PA Racing Limited | Arts & recreation | 2021 |
| PA Sports Marketing Limited | Arts & recreation | 2025 |
| Pace MRI Ltd | Professional & scientific | 2025 |
| Padel Union Ltd | Arts & recreation | 2024 |
| Paint Application Technologies Limited | Professional & scientific | 2006 |
| Paladin Business Services Limited | Real estate | 2005 |
| Palliser Road RTM Company Limited | Households | 2012 |
| Palus Limited | Professional & scientific | 2010 |
| Panamex - PAN American Exports Limited | Wholesale & retail | 1978 |
| Panat Property Limited | Real estate | 2025 |
| Panta Mogeta Ltd | Wholesale & retail | 2017 |
| Panthera Properties Ltd | Real estate | 2022 |
| Paramount Finance Co.,Limited | Financial services | 1946 |
| Paramount Floors Ltd | Construction | 2019 |
| Paregaso Group Limited | Administrative & support | 2019 |
| Park House (Berkhamsted) Management Co. Limited | Households | 2005 |
| Park Tuition Limited | Education | 2018 |
| Parkviews Consulting Ltd | Professional & scientific | 2018 |
| Participators Investment Company Limited(The) | Real estate | 1937 |
| Patchland Sound Services Ltd | Information & communication | 2025 |
| Patrolmake Limited | Hospitality | 1996 |
| PAU7Y Ltd | Professional & scientific | 2024 |
| Paul Crane Rigging Limited | Construction | 2019 |
| Paul Robinson Consulting Limited | Professional & scientific | 2017 |
| Paws the Planet Ltd | Wholesale & retail | 2020 |
| Payne Automation Limited | Information & communication | 2017 |
| Payroll Bureau Services Limited | Administrative & support | 2016 |
| PB New Homes Limited | Construction | 2023 |
| PBR Developments Ltd | Construction | 2011 |
| PBR Property Investments Limited | Real estate | 2020 |
| PBR Roofing Limited | Construction | 2016 |
| PBR Solar Ltd | Construction | 2026 |
| PCJ Estates Ltd | Real estate | 2024 |
| Pcpt Consulting Limited | Information & communication | 2026 |
| Pcssv Group Ltd | Real estate | 2025 |
| PD IT Solutions Ltd | Information & communication | 2012 |
| Peace of Mind PA Services Ltd | Information & communication | 2013 |
| Peak Pacific (UK) Limited | Information & communication | 1998 |
| Pegasus Place MGT Limited | Households | 2026 |
| Peggy Tully Limited | Professional & scientific | 2025 |
| Pellego Solutions Ltd | Professional & scientific | 2023 |
| Pentagon London Ltd | Wholesale & retail | 2015 |
| Pentex Property Co. Limited | Real estate | 1979 |
| Perch Foundry Ltd | Hospitality | 2025 |
| Perevale Consulting Services Limited | Real estate | 2002 |
| Performance Holdings Limited | Real estate | 2017 |
| Perpetual Properties Ltd | Real estate | 2003 |
| Perry Corp Limited | Professional & scientific | 2024 |
| Perrypropertymanagement Ltd | Real estate | 2024 |
| Personally Virtual Ltd | Administrative & support | 2019 |
| Pet Care Special Limited | Wholesale & retail | 2008 |
| Peter Grunert Limited | Information & communication | 2020 |
| Peter James Developments Ltd | Real estate | 2024 |
| Petronio Partners Ltd | Professional & scientific | 2018 |
| Pexton Searle CRM Services Limited | Real estate | 2003 |
| Pharmakia Ltd | Professional & scientific | 2012 |
| Phetone Limited | Real estate | 1978 |
| Philip Binfield Limited | Financial services | 1971 |
| Philip Binfield Taxation Services Limited | Professional & scientific | 1989 |
| Phillips Direct Limited | Manufacturing | 1984 |
| Phillips Doors & Windows Limited | Construction | 2026 |
| Phillips Presentation Products Limited | Professional & scientific | 2000 |
| Phillips Property and Investments Ltd | Real estate | 2024 |
| Philosophy Property Ltd | Real estate | 2024 |
| Phoenix Domestic and Commercial Cleaning Limited | Other services | 2017 |
| Phoenix Osteopathy Ltd | Health & social care | 2014 |
| Pico Services Ltd | Information & communication | 2007 |
| Piece of Cake (Events) Ltd | Other services | 2008 |
| Piitch Limited | Administrative & support | 2024 |
| Pinchin Architects Ltd. | Professional & scientific | 2007 |
| Pink Recruitment Services Ltd | Administrative & support | 2024 |
| PJW Marketing Limited | Extraterritorial | 2015 |
| PKL Electrical Services Limited | Construction | 2006 |
| PL Van Limited | Transport & logistics | 2026 |
| Platinum Building Services Ltd | Construction | 2025 |