| NYX Labs Ltd | Information & communication | 2025 |
| Oakfield Surveyors Ltd | Professional & scientific | 2021 |
| Oakwood Place (Lane END) Residents Management Company Limited | Households | 2015 |
| Objectiv Limited | Professional & scientific | 2025 |
| OBM Holdings Ltd | Real estate | 2020 |
| Obsidian Alliance Ltd | Information & communication | 2026 |
| Obsidian Capital Advisory Limited | Professional & scientific | 2019 |
| Ocean Electrical Installations Ltd | Construction | 2025 |
| Odamedo Ltd | Manufacturing | 2021 |
| Odyssey Properties Ltd | Real estate | 2023 |
| Odyssia Holdings 2 Limited | Professional & scientific | 2025 |
| Odyssia Holdings Ltd | Financial services | 2019 |
| Odyssia Investments Ltd | Financial services | 2024 |
| Odyssia Properties Ltd | Real estate | 2024 |
| OH Wellbeing Ltd | Health & social care | 2014 |
| OIL Industries Club Limited(The) | Other services | 1981 |
| Olcote Ltd | Real estate | 2023 |
| Old Bank House Management Company Limited | Households | 2006 |
| Old Park Mews Management Limited | Households | 2019 |
| Old PO Consulting Limited | Professional & scientific | 2018 |
| Olive Tree Marlow Ltd | Hospitality | 2018 |
| Oliver James Consultancy Ltd | Professional & scientific | 2026 |
| Oliver Moon Limited | Arts & recreation | 1967 |
| Olivetree Restaurant Marlow Ltd | Hospitality | 2020 |
| Olivia Jerrard Limited | Arts & recreation | 2026 |
| Omonic Ltd | Information & communication | 2015 |
| ON Board Advisory Ltd | Professional & scientific | 2023 |
| On-Par Publishing Limited | Wholesale & retail | 2006 |
| One Call Maintenance Group Ltd | Construction | 2015 |
| One Group Solutions Ltd | Water & waste | 2020 |
| One Menagerie Ltd | Professional & scientific | 2014 |
| Onevanwonder Limited | Transport & logistics | 2026 |
| Only Something Ltd | Financial services | 2023 |
| Onlyeverything Ltd | Professional & scientific | 2023 |
| Ontalento Ltd | Wholesale & retail | 2014 |
| Opal House Limited | Real estate | 2025 |
| Open Mind Productions Limited | Information & communication | 1989 |
| OPEN4ENERGY Limited | Professional & scientific | 2002 |
| Oppo Connect Limited | Professional & scientific | 2015 |
| Oppo Recruitment Limited | Administrative & support | 2013 |
| Optimizer Health Limited | Wholesale & retail | 2026 |
| Optum Health Solutions (UK) Limited | Professional & scientific | 2013 |
| Optum Solutions UK Holdings Limited | Professional & scientific | 2009 |
| Optum UK Solutions Group Limited | Financial services | 2007 |
| Orange Pill Creative Ltd | Professional & scientific | 2025 |
| Orangebook-Hr Ltd | Administrative & support | 2018 |
| Orchard House (I.F.A.S) Ltd. | Financial services | 1994 |
| Orchid Landscaping & Management Company Ltd | Other services | 2020 |
| Orchid Property Holdings Ltd | Other services | 2019 |
| Orion Partners (Professional Advisors) LLP | | 2002 |
| Orlando Productions Limited | Information & communication | 2014 |
| OT Building Blocks Therapy Ltd | Health & social care | 2023 |
| Outdoor & Indoor Living Limited | Wholesale & retail | 2010 |
| Outer Space Garden Buildings Ltd | Construction | 2010 |
| Overseas Community Forum Limited | Health & social care | 2025 |
| Overview Outreach Ltd | Extraterritorial | 2003 |
| Oxcenbright Ltd | Extraterritorial | 2023 |
| Oxford Land Investments Ltd | Construction | 2013 |
| Oxford Medical Group Ltd | Health & social care | 2021 |
| Oxford Wireless Limited | Wholesale & retail | 2017 |
| P Davenport Ltd | Real estate | 2020 |
| P Waterman Carpentry Limited | Construction | 2016 |
| P.I. Works UK Ltd | Information & communication | 2016 |
| P12 Communications Limited | Professional & scientific | 2015 |
| P3 Management Consultants Ltd | Professional & scientific | 2014 |
| Paintscene Ltd | Construction | 2014 |
| Paish Consult Ltd | Administrative & support | 2017 |
| Paish Properties Ltd | Construction | 2018 |
| Palladia Bidco Limited | Financial services | 2022 |
| Palladia Midco Limited | Financial services | 2022 |
| Palladia Topco Limited | Financial services | 2022 |
| Palm (UK) Limited | Information & communication | 2004 |
| Papillon Investments Ltd | Real estate | 2021 |
| Paradigm Shift (UK) Limited | Information & communication | 1997 |
| Parcelhub Limited | Transport & logistics | 2010 |
| Park Lawn Management Co. Limited | Households | 1985 |
| Parkfranks Ltd | Arts & recreation | 2026 |
| Parkinspaces Limited | Administrative & support | 2008 |
| Partbeck Limited | Health & social care | 2022 |
| Pathfinder Asset Management Limited | Professional & scientific | 2022 |
| Pathfinder Wealth Management Ltd | Financial services | 2021 |
| Pathways Tutoring Ltd | Education | 2026 |
| Paul Rowlinson Consulting Limited | Professional & scientific | 2022 |
| Paula Figgett Limited | Administrative & support | 2013 |
| Paws 4 Thought Dogs Ltd | Administrative & support | 2018 |
| Payton Mews Residents Management Company Limited | Households | 2014 |
| Pdsd Consulting LLP | | 2009 |
| Peerland House Management Limited | Real estate | 2012 |
| Pegasus Quality Services Limited | Information & communication | 2013 |
| Pegasus Way Haddenham Management Limited | Households | 2016 |
| Pelyras Services Limited | Extraterritorial | 2022 |
| Pembroke Care Limited | Health & social care | 2006 |
| Penguin Fish Bar Limited | Hospitality | 2019 |
| Penwood Court Residents Limited | Households | 1994 |
| People in Places Limited | Administrative & support | 2007 |
| People in Power Limited | Administrative & support | 2021 |
| People WHO Know Limited | Administrative & support | 2017 |
| People-Star Limited | Administrative & support | 2016 |
| Perdact Ltd | Professional & scientific | 2023 |
| Perfector Arasys & Sysara Skin Ltd | Other services | 2024 |