| Orange Cyberdefense UK Limited | Information & communication | 2002 |
| Orange Grove Events Limited | Arts & recreation | 2023 |
| Orange Room Creative Limited | Professional & scientific | 2026 |
| Orbit FFE Ltd | Wholesale & retail | 2023 |
| Orbit HQ Ltd | Information & communication | 2025 |
| Orbit Lead Generation Limited | Professional & scientific | 2024 |
| Orchard (Estate Management) Limited | Construction | 1988 |
| Orchard Academy Trust | Education | 2012 |
| Orchard Centre Management Limited | Real estate | 1991 |
| Orchard Cooling Ltd | Manufacturing | 2017 |
| Orchard Gate (Kent) Management Limited | Households | 2013 |
| Orchard View (Management Company) Ltd | Real estate | 2018 |
| Orchard View Classics Limited | Wholesale & retail | 2016 |
| Orchard View Garage Limited | Wholesale & retail | 2002 |
| Orchids of Life Healthcare Ltd | Health & social care | 2022 |
| Organic Marketing Limited | Extraterritorial | 2014 |
| Orion Building Solutions Limited | Construction | 2012 |
| Ormonde Court Putney RTM Limited | Households | 2004 |
| Ornius Limited | Information & communication | 2025 |
| Orniva Ltd | Manufacturing | 2024 |
| Oronerouk Ltd | Hospitality | 2024 |
| Orpik Homes Ltd | Construction | 2022 |
| Orpik Ltd | Construction | 2022 |
| Orselina Property Limited | Real estate | 2022 |
| Orselina Rentals Ltd | Real estate | 2024 |
| Osabea Healthcare Solutions Limited | Health & social care | 2023 |
| Osborne Architecture & Planning Limited | Professional & scientific | 2020 |
| Osburns Independent Traders Ltd | Real estate | 2015 |
| Oscal Consulting Limited | Administrative & support | 2010 |
| Oscar Vicarage Limited | Professional & scientific | 2016 |
| Oscarjames Ltd | Construction | 2004 |
| Oscarvltr Limited | Information & communication | 2021 |
| Osdistributor Ltd | Wholesale & retail | 2025 |
| Osint Service Ltd | Construction | 2016 |
| OSK Group Ltd | Transport & logistics | 2016 |
| OSS Consult Limited | Professional & scientific | 2018 |
| Ossify Education Ltd | Education | 2026 |
| Ostrimark Investments Ltd | Professional & scientific | 2013 |
| OT 4 Independence Ltd | Health & social care | 2016 |
| OT INT Limited | Administrative & support | 2024 |
| Otetela Health Ltd | Public administration | 2020 |
| Othen Mortgage Planning Ltd | Financial services | 2021 |
| OTP Management Limited | Arts & recreation | 2022 |
| Ottoman Estates Limited | Real estate | 1996 |
| Otusegi Properties Ltd | Real estate | 2025 |
| OUR First Story Ltd | Wholesale & retail | 2017 |
| OUR Story Magic.Ai Ltd | Information & communication | 2025 |
| OUR Surveyors Limited | Professional & scientific | 2021 |
| Ouraeon Limited | Administrative & support | 2025 |
| OUT of the Brick Ltd | Real estate | 2023 |
| Outdoor Schemes Ltd | Construction | 2026 |
| Outdoorsy Living Limited | Administrative & support | 2012 |
| Outerspace Designs Limited | Professional & scientific | 2007 |
| Outreach Tuition Ltd | Education | 2018 |
| Outstanding Compliance Ltd | Administrative & support | 2024 |
| Ovation Health Solutions Ltd | Financial services | 2024 |
| Over the Line Consultancy Ltd | Education | 2003 |
| Overcut Strategy Ltd | Information & communication | 2025 |
| Ovise Limited | Administrative & support | 2024 |
| Owen Maughan Paving & Landscaping Limited | Construction | 2025 |
| Owlin Estates CIC | Households | 2025 |
| Owls Nursery School Ltd | Education | 2015 |
| OX Brewery Installation and Technical Services Ltd | Hospitality | 2019 |
| Oxbridge Tuition Services (UK) Ltd | Education | 2025 |
| Oxford Tiling Services Ltd | Construction | 2026 |
| Oxlea Property Company Ltd | Real estate | 2014 |
| Oxlow Lane Limited | Real estate | 2019 |
| Oxon Hoath Country Estate Ltd | Real estate | 2024 |
| Oxted Window Systems Ltd | Manufacturing | 1996 |
| OYA Soulful Publications Ltd | Information & communication | 2024 |
| OZ Car Valeting Ltd | Administrative & support | 2026 |
| OZ Media Tech Limited | Transport & logistics | 2024 |
| Ozone Homes Ltd | Professional & scientific | 2011 |
| P & K Property Maintenance Limited | Real estate | 2004 |
| P & L Contracts (South) Ltd | Construction | 2002 |
| P & W Cars Limited | Wholesale & retail | 2025 |
| P a Collins Brickwork Ltd | Construction | 2021 |
| P Arter & SON Builders Limited | Construction | 2011 |
| P D J Developments Limited | Other services | 2012 |
| P D Tankers Ltd | Transport & logistics | 2023 |
| P E Services (Kent) Limited | Construction | 2011 |
| P H C Health & Safety Ltd. | Health & social care | 2002 |
| P Hutchins UK Limited | Real estate | 2013 |
| P J Insurance Services Limited | Financial services | 2008 |
| P J V Learning and Development Ltd | Education | 2006 |
| P Wright Engineering Services Limited | Manufacturing | 2013 |
| P&J Homes Ltd | Real estate | 2015 |
| P&Lau Limited | Professional & scientific | 2024 |
| P&M Property Services Ltd | Construction | 2021 |
| P&S Gamwell Ltd | Construction | 2023 |
| P. Barber Electrical Ltd | Construction | 2023 |
| P. Watts Solutions Limited | Construction | 2025 |
| P.C. Blinds Limited | Manufacturing | 1998 |
| P.D.C. (Piling) Limited | Construction | 2005 |
| P.D.T Pyrotechnic Defence Technologies Limited | Professional & scientific | 2022 |
| P.E.C Financial Ltd | Financial services | 2021 |
| P.J. Denton Limited | Construction | 1979 |
| P.J.J Social Care Limited | Health & social care | 2019 |
| P.J.J.S. Management Services Limited | Real estate | 1979 |
| P.W. Goddard Ceramic Tiling Limited | Construction | 1994 |