| Office Planters Limited | Administrative & support | 2008 |
| Offord Property Investments Ltd | Real estate | 2021 |
| OK2LAND Limited | Other services | 2018 |
| Old Barn Audio Limited | Administrative & support | 2007 |
| Old Bell Wooburn Limited | Hospitality | 2014 |
| Old Pottery International Ltd | Real estate | 2022 |
| Old Pottery Limited | Administrative & support | 2008 |
| Old Pottery Wealth Management Limited | Administrative & support | 2004 |
| Olive and Rose Childrenswear Ltd | Wholesale & retail | 2025 |
| Oliver & Bailey Property Management Limited | Real estate | 2015 |
| Oliver Block Management Ltd | Real estate | 2026 |
| Oliver Groceries Ltd | Wholesale & retail | 2024 |
| ON Fire Productions Limited | Real estate | 2016 |
| ON Top Roofing & Guttering Ltd | Construction | 2024 |
| Once Construction Ltd | Construction | 2023 |
| One Threadneedle Limited | Financial services | 2019 |
| Only Fish Ltd | Agriculture & fishing | 2023 |
| Onward Graphic Studio Limited | Professional & scientific | 2022 |
| Onyx Recordings Ltd | Wholesale & retail | 2018 |
| Ooshka Ltd | Professional & scientific | 2025 |
| Opecsystem Limited | Information & communication | 1985 |
| Opelstone Properties Ltd | Real estate | 2024 |
| Opsync AI Limited | Information & communication | 2024 |
| Optimise Potential Ltd | Health & social care | 2024 |
| Optimum Media Services Limited | Professional & scientific | 2003 |
| Orange Rock Limited | Information & communication | 2016 |
| ORB Minigolf Limited | Arts & recreation | 2022 |
| Orca Technical Solutions Ltd | Manufacturing | 2025 |
| Orchard Realty Investments Ltd | Real estate | 2025 |
| Origanum Limited | Wholesale & retail | 2020 |
| Orizzonti Consulting Ltd | Professional & scientific | 2020 |
| Orthoacumen Ltd | Information & communication | 2026 |
| Osinq Limited | Professional & scientific | 2016 |
| Osmon Construction Limited | Construction | 2008 |
| Othello Payrolling Ltd | Administrative & support | 2021 |
| Other Duck Designs Limited | Information & communication | 2017 |
| Otterholt Property Ltd | Real estate | 2025 |
| Outlive Limited | Professional & scientific | 2023 |
| Over the MOO Dairy Ltd | Manufacturing | 2023 |
| Owen Contracting Limited | Construction | 2010 |
| Owen Contractors Holdings Limited | Financial services | 2007 |
| Owen Contractors Limited | Construction | 1999 |
| Owen Events Ltd | Professional & scientific | 2021 |
| Owen Mortgage Services Limited | Extraterritorial | 2005 |
| Owen Scaffold Contractors Limited | Construction | 1995 |
| OWL Artist Management Ltd | Administrative & support | 2014 |
| Oxford Anaesthesia LLP | | 2023 |
| P a Taylor Building & Block Paving Limited | Construction | 2004 |
| P and P Building and Renovations Limited | Construction | 2016 |
| P Chadwick Limited | Professional & scientific | 1998 |
| P Hudson Painter & Decorator Limited | Construction | 2003 |
| P J Hopkins Investments Limited | Administrative & support | 2024 |
| P Lulham Developments Ltd | Construction | 2022 |
| P Markwick & SON Limited | Construction | 2005 |
| P T Systems Limited | Construction | 2006 |
| P. S. F. Driving Services Limited | Transport & logistics | 2008 |
| P.B. Wheatley Ltd | Construction | 2002 |
| P.J.C Property Consultants Ltd | Real estate | 2011 |
| Pace Property Rentals Ltd | Real estate | 2022 |
| Pace Real Estate Ltd | Real estate | 2022 |
| Paddocks (Upper Dicker) Management Company Limited | Households | 2026 |
| Pagscaffolding 2026 Limited | Construction | 2026 |
| Palehouse Ltd | Wholesale & retail | 2023 |
| Pali Construction Limited | Manufacturing | 2014 |
| Palling & Co Limited | Administrative & support | 2023 |
| Palmers Turfcare Limited | Administrative & support | 2005 |
| Paloma Publishing Limited | Information & communication | 2010 |
| Palomino Productions Limited | Information & communication | 2016 |
| Panda Property Investments Limited | Real estate | 2017 |
| Panther Fire Solutions Ltd | Construction | 2021 |
| Panther Fire Technologies Ltd | Public administration | 2025 |
| Paper Options Limited | Other services | 2011 |
| Paragon Adhesives Holdings Limited | Financial services | 2001 |
| Paragon Adhesives Limited | Wholesale & retail | 1985 |
| Paramount Property and Construction Services Limited | Construction | 2004 |
| Parent Approved Ltd | Wholesale & retail | 2026 |
| Pareon Chemicals Limited | Manufacturing | 2011 |
| Parkgrove Recruitment Limited | Professional & scientific | 2006 |
| Parkside Clapham Holdings Limited | Financial services | 2016 |
| Partners 4 Training Ltd. | Education | 2003 |
| Partners Tea & Coffee Limited | Wholesale & retail | 1983 |
| Pass IT on in Your Community CIC | Hospitality | 2022 |
| Patchwerk Limited | Other services | 2014 |
| Paul Smith Building Contractors Ltd | Construction | 2015 |
| Paul Soane Marine Services Limited | Manufacturing | 2024 |
| Pawfect Pals Limited | Other services | 2024 |
| Pawlowski Engineering Limited | Professional & scientific | 2008 |
| Payment Pros Ltd | Professional & scientific | 2021 |
| Payne Drylining Limited | Construction | 2026 |
| Paynes Smart Repairs Ltd | Wholesale & retail | 2026 |
| PCM Estate Agents Online Limited | Real estate | 2017 |
| PCM Property Holdings Limited | Financial services | 2017 |
| PDT Electrical Services Ltd | Construction | 2015 |
| Peach Power Fit Limited | Arts & recreation | 2023 |
| Peak Diagnostics LLP | | 2026 |
| Pearce. Build - Extend - Convert Ltd | Construction | 2016 |
| Peartree Financial Services Ltd | Financial services | 2023 |
| Peartree Orthopaedics Ltd | Health & social care | 2026 |
| Pebsham Equestrian Centre Ltd | Arts & recreation | 2020 |
| Pegg-Air Ltd | Transport & logistics | 2022 |