| PCR (London) LLP | | 2010 |
| PD Financial Management & Business Partners Limited | Professional & scientific | 2022 |
| PDF Supplies Limited | Wholesale & retail | 2022 |
| Pdub Enterprise Limited | Professional & scientific | 2016 |
| Pdubz Limited | Wholesale & retail | 2017 |
| Peace Counselling Ltd | Health & social care | 2023 |
| Pedal Premises Limited | Households | 2025 |
| Pehrsson Scott Ltd | Professional & scientific | 2018 |
| Pelican Red Limited | Administrative & support | 2019 |
| Pelican White Services Limited | Administrative & support | 2016 |
| Peniston Services Ltd | Administrative & support | 2022 |
| Penrhos Limited | Hospitality | 1993 |
| Penrobia Investments Ltd | Real estate | 2002 |
| Pepper Property Services Ltd | Construction | 2023 |
| Peppermint Hippo Limited | Real estate | 2024 |
| Perani̇ce Ltd | Professional & scientific | 2021 |
| Performance Concept Logistic Services Limited | Transport & logistics | 2019 |
| Perrin Myddelton Limited | Professional & scientific | 2016 |
| Perrins Solicitors LLP | | 2009 |
| Perry Green Homes Ltd | Construction | 2024 |
| Peter & Geraldine Ward LLP | | 2025 |
| PGF Holdings Limited | Financial services | 2021 |
| PGJ Accounting Solutions Limited | Professional & scientific | 2018 |
| PGU Residential Ltd | Construction | 2019 |
| Pharmabiz Ltd | Professional & scientific | 2013 |
| Pharmonise Limited | Wholesale & retail | 2004 |
| Phase 1 Oakfield Road Management (Harpenden) Limited | Administrative & support | 1998 |
| Pherosyn Ltd | Manufacturing | 2020 |
| PHI Infinity Limited | Real estate | 2005 |
| Phil Holt & SON Limited | Agriculture & fishing | 2016 |
| Philanthrify Ltd | Information & communication | 2023 |
| Phoenix House (ST Albans) Management Company Limited | Administrative & support | 2007 |
| Phoenix London INV Ltd | Real estate | 2019 |
| Photozi Limited | Professional & scientific | 2022 |
| Phytoform Labs Ltd | Professional & scientific | 2017 |
| PI Progress Ltd | Professional & scientific | 2018 |
| Picco Bello Designs Ltd | Other services | 2014 |
| Pierce Ltd | Information & communication | 2017 |
| Pinewood (Harpenden) Management Company Limited | Households | 2015 |
| Pinkney Interiors Ltd | Professional & scientific | 2020 |
| Pither Landscaping & Construction Ltd | Construction | 2024 |
| PJC Motorsport Limited | Wholesale & retail | 2025 |
| Plane Sailing Games Limited | Information & communication | 2019 |
| Planet POS Limited | Professional & scientific | 2011 |
| Plastic Surgery International Limited | Health & social care | 2016 |
| Platform Shape Ltd | Information & communication | 2026 |
| Platform Wines Limited | Wholesale & retail | 2019 |
| Platinum Housekeeping Limited | Administrative & support | 2013 |
| Plinth Consultancy Limited | Professional & scientific | 2018 |
| PLN Facilities Limited | Information & communication | 2002 |
| Plowman Craven Limited | Professional & scientific | 2007 |
| Plowman Craven US Holdco Limited | Administrative & support | 2024 |
| PLS Consulting Ltd | Professional & scientific | 2023 |
| Plumb Marshall Ltd | Construction | 2020 |
| Plutus Collective Limited | Professional & scientific | 2025 |
| POA Tree Limited | Administrative & support | 2020 |
| Podium Performance Ltd | Wholesale & retail | 2020 |
| Pointforce Limited | Professional & scientific | 2006 |
| Pollards Farm Ltd. | Wholesale & retail | 2016 |
| Ponder Productions Limited | Information & communication | 2003 |
| Pondsmeade Residents Company Limited | Households | 2006 |
| Poppyfish People Development Ltd | Professional & scientific | 2012 |
| Populi Solutions Ltd | Professional & scientific | 2025 |
| Portable LOO Hire Solutions Ltd | Administrative & support | 2021 |
| Portofino Harpenden Ltd | Hospitality | 2023 |
| Portsoken Associates Ltd | Professional & scientific | 2019 |
| Portsoken Investment Ltd | Financial services | 2019 |
| POS Trustees Limited | Administrative & support | 2023 |
| Poteris CIC | Information & communication | 2020 |
| Pousto Limited | Financial services | 2026 |
| POW Talent Agency Limited | Arts & recreation | 2024 |
| POW TV Studios Limited | Information & communication | 2020 |
| Power House Entertainment Ltd | Arts & recreation | 2025 |
| Power Office Services Limited | Administrative & support | 2001 |
| Practice Advisory Group Ltd | Professional & scientific | 2026 |
| Practise Music Limited | Arts & recreation | 2017 |
| Prayon (UK) Public Limited Company | Wholesale & retail | 1976 |
| PRC Gardens Ltd | Administrative & support | 2021 |
| PRE FC Limited | Professional & scientific | 2018 |
| Premier Prestige Ltd | Wholesale & retail | 2015 |
| Premiere Outdoor Limited | Professional & scientific | 2006 |
| Prep Matter Limited | Professional & scientific | 2019 |
| Prestige Optical Limited | Information & communication | 2021 |
| Pretty Pet Care Ltd | Other services | 2020 |
| Preveza Consulting Ltd | Information & communication | 2018 |
| Primus Construction Limited | Construction | 2011 |
| Primus Holdings Limited | Financial services | 2015 |
| Primus Tento Ltd | Information & communication | 2020 |
| Printers Court Management Company (ST. Albans) Limited | Households | 1992 |
| Priory Maintenance (Redbourn) Limited | Households | 1972 |
| Pritchard Enterprises Limited | Real estate | 2017 |
| Private Clients UK Limited | Other services | 2016 |
| Private Equity Communications Limited | Administrative & support | 2021 |
| Private Homecare Services Limited | Health & social care | 2024 |
| Probateadmin Ltd | Information & communication | 2019 |
| Probets Building Ltd | Construction | 2025 |
| Proctor Support Services Limited | Administrative & support | 2025 |
| Prodata Limited | Administrative & support | 1978 |
| Prodigus Projects Limited | Professional & scientific | 2008 |
| Production Physiotherapy Limited | Health & social care | 2018 |