| Opus Aqua Ltd | Professional & scientific | 2017 |
| Opus Eroica Ltd | Financial services | 2025 |
| Opustract Limited | | 1989 |
| OR Tiling Ltd | Construction | 2013 |
| Oraa Enterprises Limited | Real estate | 2026 |
| Oracle Cars Ltd | Transport & logistics | 2023 |
| Orange Dog Consulting Ltd | Professional & scientific | 2025 |
| Orange Tree Events Ltd | Administrative & support | 1996 |
| Orbis Ceramics Ltd | Wholesale & retail | 2026 |
| Orbo Ltd | Wholesale & retail | 2023 |
| Orca Consult Ltd | Professional & scientific | 2025 |
| Orca-Strait Consulting Limited | Professional & scientific | 2025 |
| Orcaflow Ltd | Information & communication | 2025 |
| Orchard Business Management Limited | Professional & scientific | 2017 |
| Orchard Cottages 1967 Limited | Extraterritorial | 2014 |
| Orchard Financial Consultancy Limited | Professional & scientific | 2019 |
| Orchard House Ascot Limited | Households | 2025 |
| Orchard Way Residents Society Limited | Households | 1970 |
| Orchards Accountants Limited | Professional & scientific | 2023 |
| Orchid Energy Ltd | Construction | 2022 |
| Ordas IT Limited | Information & communication | 2014 |
| Orecroft Registrars Limited | Professional & scientific | 2000 |
| Oriental Road (Bramshill) Residents Association Limited | Households | 1986 |
| ORIGIN8 Real Estate Limited | Real estate | 2022 |
| Orion Partners LLP | | 2009 |
| Orlando Stuart Films Ltd | Information & communication | 2019 |
| Orphic Financial Insight Limited | Professional & scientific | 2023 |
| Orsini Estate Ltd | Construction | 2024 |
| Ortisei Consulting Limited | Information & communication | 2023 |
| Orwell Heath Homes Ltd | Construction | 2023 |
| OS Accounting Limited | Professional & scientific | 2018 |
| OS3 Consulting Limited | Information & communication | 2015 |
| Oshiga-Lalli Limited | Real estate | 2020 |
| Osiris Advisors Limited | Professional & scientific | 2010 |
| Oska Properties Limited | Real estate | 2023 |
| Oskins Management Limited | Households | 1983 |
| OSM Surrey Ltd | Arts & recreation | 2022 |
| Osmosis Events Limited | Other services | 2011 |
| Otisuki Ltd | Real estate | 2022 |
| Ottershaw Auto & Tyre Centre Ltd | Wholesale & retail | 2026 |
| Otto and JJ Limited | Other services | 2022 |
| Otto Group Ltd | Construction | 2018 |
| Otumn Bloom Limited | Information & communication | 2014 |
| Ourbizz Limited | Information & communication | 2026 |
| Outram Enterprises Ltd | Real estate | 2013 |
| Outram Leisure Limited | Wholesale & retail | 2017 |
| Outside Edge Creative Ltd | Professional & scientific | 2024 |
| Outside Inn Glamping Ltd | Hospitality | 2022 |
| Outside-Inns (UK) Limited | Hospitality | 2008 |
| Outspot Commercial Cleaning Services Ltd | Administrative & support | 2018 |
| Ouuzart Limited | Wholesale & retail | 2025 |
| OVA4 Limited | Wholesale & retail | 2024 |
| Ovenology Pizza & Grill Ltd | Hospitality | 2025 |
| Over to Solar Ltd | Construction | 2022 |
| Overneath Limited | Information & communication | 2014 |
| Overview Limited | Manufacturing | 1988 |
| Owen Partnership LLP | | 2025 |
| Owletech Ltd | Professional & scientific | 2025 |
| Oxadenario Ltd | Manufacturing | 2025 |
| Oxbridge Tutors Limited | Education | 1997 |
| Oxford Consultancy Group Limited | Professional & scientific | 2020 |
| Oxford Consulting Group Limited | Administrative & support | 1991 |
| Oxford Consulting Holdings Limited | Administrative & support | 2016 |
| Oxford EBT Limited | Professional & scientific | 2026 |
| Oxford Holdings Group Limited | Professional & scientific | 2026 |
| Oxford Sales and Marketing Limited | Professional & scientific | 2015 |
| Oxfordsm Limited | Professional & scientific | 1986 |
| Oxyo Logistics Group Ltd | Transport & logistics | 2026 |
| Oxyo Logistics Ltd | Transport & logistics | 2026 |
| OZ Properties Limited | Real estate | 2001 |
| OZO Limited | Administrative & support | 2006 |
| P B Kids Ltd | Arts & recreation | 2023 |
| P B Painting Limited | Construction | 2022 |
| P B South West Ltd | Arts & recreation | 2023 |
| P V Capital Management Limited | Real estate | 2024 |
| P&M Investments Ltd | Real estate | 2025 |
| P.A. for a Day Limited | Hospitality | 2001 |
| P2 Squared Business Services Limited | Professional & scientific | 2017 |
| Pablo Barbers Limited | Other services | 2023 |
| Pabsco Limited | Professional & scientific | 1996 |
| Pach Solutions Ltd | Professional & scientific | 2012 |
| Pacific Bluebay Limited | Professional & scientific | 2013 |
| Paddington Dental Partnership Limited | Health & social care | 2011 |
| Paddlefish Panda Ltd | Professional & scientific | 2019 |
| Padel Apparel Ltd | Manufacturing | 2024 |
| Padel Club & Co UK Ltd | Construction | 2021 |
| Padlock Chippenham South Limited | Real estate | 2023 |
| Padlock Dunstable Limited | Real estate | 2022 |
| Padlock Edmonton Limited | Real estate | 2023 |
| Padlock Huntingdon Limited | Real estate | 2021 |
| Padlock Southend Limited | Real estate | 2022 |
| Padlock UK Bidco 10 Limited | Real estate | 2025 |
| Padlock UK Bidco 2 Limited | Real estate | 2020 |
| Padlock UK Bidco 3 Limited | Real estate | 2020 |
| Padlock UK Bidco 4 Limited | Real estate | 2020 |
| Padlock UK Bidco 5 Limited | Real estate | 2021 |
| Padlock UK Bidco 6 Limited | Real estate | 2022 |
| Padlock UK Bidco 7 Limited | Real estate | 2022 |
| Padlock UK Bidco 8 Limited | Real estate | 2023 |
| Padlock UK Bidco 9 Limited | Real estate | 2023 |