| Oléhub Limited | Arts & recreation | 2024 |
| Omada Investments Limited | Financial services | 2022 |
| Omar Lodge RTM Company Limited | Households | 2011 |
| Omega Contract Management Ltd | Professional & scientific | 2017 |
| Omkara Limited | Real estate | 2020 |
| Omni Retail Ltd | Administrative & support | 2021 |
| Omnia Clinics Limited | Health & social care | 2024 |
| Omnia Engineering Services Limited | Construction | 2023 |
| Omnia Realty Limited | Health & social care | 2025 |
| Omnibus ABC CIC | Education | 2026 |
| OMS Software Consultancy Limited | Information & communication | 2019 |
| ON Top Teaching Ltd | Education | 2025 |
| One Acre Homes Ltd | Real estate | 2025 |
| One Global Property Services (UK) Limited | Real estate | 2019 |
| One Stop Cleaning Services Limited | Administrative & support | 2026 |
| One Way Cleaning Ltd | Administrative & support | 2022 |
| Onlygraded Ltd | Other services | 2022 |
| Onmax Estates Limited | Real estate | 2024 |
| Onsite Spraying Solutions Ltd | Construction | 2026 |
| Onur OZ Ltd | Manufacturing | 2020 |
| OOH Creative Ltd | Professional & scientific | 2026 |
| Opalway Limited | Households | 1998 |
| Opas I.T. Limited | Information & communication | 1999 |
| Opeshold Ltd | Financial services | 2016 |
| OPS Construction Limited | Construction | 2019 |
| Optimum Electrical Solutions Ltd | Construction | 2013 |
| Optimum Strategic Communications Ltd. | Professional & scientific | 2017 |
| Optimus Carpentry Ltd | Construction | 2018 |
| Opulence Gallery Limited | Wholesale & retail | 2021 |
| Opulent Flooring Ltd | Construction | 2023 |
| OPX Studio Limited | Professional & scientific | 2024 |
| Oracle (Indescon) Limited | Real estate | 2006 |
| Orak Investments Ltd | Real estate | 2022 |
| Orbit & Anchor Ltd | Professional & scientific | 2016 |
| Orbitcove Limited | Real estate | 1996 |
| Orcades Security & Protection Consultancy Limited | Administrative & support | 2026 |
| Orchard Brickwork Limited | Construction | 2013 |
| Orchard Caravan Storage Limited | Transport & logistics | 2001 |
| Orchard Cottage Ltd | Real estate | 2020 |
| Orchard Wharf Developments Limited | Construction | 2015 |
| Orchari Limited | Wholesale & retail | 2025 |
| Order & Flow Living Limited | Other services | 2026 |
| Oreda Group Ltd | Wholesale & retail | 2025 |
| Orford House Developments Limited | Construction | 2021 |
| Orgalpha Ltd | Professional & scientific | 2025 |
| Organic Uncle Limited | Wholesale & retail | 2021 |
| Orhidea Ltd | Other services | 2017 |
| Orient Palace London Ltd | Hospitality | 2022 |
| Origin Workshop Limited | Information & communication | 2015 |
| Originalcaveman. Limited | Extraterritorial | 2023 |
| Osborn Coaching & Consultancy Limited | Education | 2026 |
| Oselo Recruitment Ltd | Administrative & support | 2018 |
| Oshima Shipbuilding Europe Limited | Administrative & support | 2023 |
| Oshprop Limited | Real estate | 2014 |
| Osiris Investments LLP | | 2014 |
| Osmia Consulting Limited | Extraterritorial | 2024 |
| OSO Group Ltd | Construction | 2017 |
| Osteo and Wellness Centre Ltd | Health & social care | 2023 |
| OSW Freehold & Management Limited | Households | 2003 |
| OTH Stansted Limited | Construction | 2026 |
| OTR OFF the Rails Ltd | Wholesale & retail | 2025 |
| Ouka Group Ltd | Financial services | 2021 |
| Oval Quarter Developments Limited | Real estate | 2011 |
| Ovingdean Hall College Limited | Education | 2010 |
| OWI Group PLC | Administrative & support | 2023 |
| OWL PUB Ltd | Hospitality | 2026 |
| Own Hold Construction Ltd | Construction | 2024 |
| Oxford ALE & Cider Investments Limited | Hospitality | 2021 |
| Oxley Park M.C. Limited | Households | 1990 |
| Oystercatcher Flying Group Limited | Manufacturing | 2021 |
| P & L F Properties Limited | Real estate | 1999 |
| P & M Interiors (UK) Limited | Construction | 2004 |
| P & Q Properties Ltd | Real estate | 2024 |
| P D S Plumbing & Heating Limited | Construction | 2008 |
| P R Access Solutions Ltd | Construction | 2017 |
| P&Cg Limited | Transport & logistics | 2008 |
| P&V Logistics Limited | Transport & logistics | 2011 |
| P.B. Taxis Limited | Transport & logistics | 2003 |
| P.C.T. Construction Limited | Construction | 2001 |
| P.F.E. Holdings Limited | Financial services | 2025 |
| P.F.E. Site Services Limited | Manufacturing | 2004 |
| P1 Homes Limited | Financial services | 2023 |
| P2 Property Ventures Limited | Real estate | 2023 |
| Pace's Pooches Ltd | Other services | 2020 |
| Packamist Limited | Administrative & support | 1993 |
| PADEL4EVERYONE (Noak Hill) Limited | Arts & recreation | 2026 |
| PADEL4EVERYONE Group Limited | Financial services | 2026 |
| PADEL4EVERYONE Ltd | Arts & recreation | 2024 |
| Padman Limited | Information & communication | 2011 |
| Paesuk Limited | Information & communication | 2016 |
| Paetoro Consulting UK Ltd | Mining & quarrying | 2016 |
| Page Crowd Ltd | Information & communication | 2025 |
| PAH Property INV Ltd | Real estate | 2025 |
| Paiger Limited | Information & communication | 2018 |
| PAL Accounts Limited | Professional & scientific | 2017 |
| Palace Group Croydon Limited | Wholesale & retail | 2018 |
| Palace Group Ruxley Limited | Wholesale & retail | 2017 |
| Palace Panels Ruxley Limited | Wholesale & retail | 2020 |
| Palisade Solutions Group Limited | Administrative & support | 2026 |
| Palm Tree Property Holdings Limited | Real estate | 2020 |