| Omcom Ltd | Construction | 2007 |
| Omionaya Limited | Professional & scientific | 2024 |
| Omnia Machinery UK Limited | Wholesale & retail | 2017 |
| Omnimach Ltd | Professional & scientific | 2024 |
| Omosefe Christina Limited | Wholesale & retail | 2021 |
| ON Chain Solutions Ltd | Information & communication | 2022 |
| ON Demand Roofing and Property Services Ltd | Construction | 2023 |
| ON Time Maintenance Ltd | Construction | 2018 |
| ON Time Properties Ltd | Real estate | 2018 |
| ON Your Turf Sports CIC | Arts & recreation | 2023 |
| On-Call Recruitment Limited | Administrative & support | 2005 |
| Ondal Finance Limited | Financial services | 2023 |
| One Blood UK Ltd | Professional & scientific | 2026 |
| One Feather Ltd | Professional & scientific | 2022 |
| One IT Services and Solutions Limited | Information & communication | 2013 |
| One More Life Limited | Education | 2018 |
| Onedan Limited | Professional & scientific | 2010 |
| Onemoregymnastics Ltd | Arts & recreation | 2024 |
| Onetran Limited | Construction | 1988 |
| Onform Help Ltd | Administrative & support | 2019 |
| Onhf Ltd | Real estate | 2025 |
| Onlyonekelsi Group Ltd | Wholesale & retail | 2025 |
| Onoma Property Limited | Real estate | 2025 |
| Onshore Real Estate Ltd | Real estate | 2023 |
| Onsite Building Trust | Real estate | 2013 |
| Onsite North East Limited Partnership | | 2009 |
| Onslow Gardens (SK) Limited | Real estate | 2022 |
| Onyx Partners Ltd | Construction | 2021 |
| OP E-Commerce Ltd | Wholesale & retail | 2023 |
| Opalmynx Limited | Professional & scientific | 2006 |
| Opalo Hair Company Ltd | Other services | 2024 |
| OPM Construction Limited | Professional & scientific | 2013 |
| OPT Business Solutions Limited | Administrative & support | 2012 |
| Optimal Golf Ltd | Education | 2023 |
| Optimal Property Investment Ltd | Real estate | 2024 |
| Optimapharma Ltd | Wholesale & retail | 2025 |
| Optionality Ltd | Professional & scientific | 2012 |
| Opus Park Subway Limited | Hospitality | 2015 |
| Oracle Childcare Centre Ltd | Education | 2018 |
| Orange Penguin Design Limited | Wholesale & retail | 2022 |
| ORB Safety Ltd | Professional & scientific | 2022 |
| Orbz Property Sourcing Ltd | Real estate | 2025 |
| Orchard County Estates Limited | Real estate | 2019 |
| Orchard County Plant Hire Limited | Administrative & support | 2019 |
| Orchard Residents' Association Limited | Other services | 1984 |
| Orchid Property Solutions Ltd | Real estate | 2015 |
| Ordwell Ltd | Financial services | 2026 |
| Organic Herbals Limited | Wholesale & retail | 2025 |
| Origin People & Culture Ltd | Professional & scientific | 2025 |
| Original Hungry Bites Ltd | Hospitality | 2020 |
| Original SYN Limited | Information & communication | 2016 |
| OSC Consultants Ltd | Administrative & support | 2017 |
| Oscar Carter Site Services Limited | Professional & scientific | 2025 |
| OTG Hospitality Ltd | Hospitality | 2024 |
| Otoengineers Ltd | Other services | 2026 |
| Ottoline Enterprise Limited | Wholesale & retail | 2025 |
| OUR Industrial Heritage CIC | Arts & recreation | 2024 |
| Outdoor Nation Ltd | Professional & scientific | 2015 |
| Outlaw Oval Racing Ltd | Wholesale & retail | 2018 |
| Outturn Limited | Professional & scientific | 2008 |
| Overview Effect Digital Ltd | Information & communication | 2025 |
| Owen Harry Building Limited | Construction | 2025 |
| Owens Business Developments Limited | Real estate | 1999 |
| OWL House Property Ltd | Real estate | 2022 |
| Owston Clinical Enterprises Ltd | Health & social care | 2022 |
| Owton Projects Ltd | Construction | 2003 |
| Oxbridge Fish Bar Limited | Hospitality | 2012 |
| Oxford Countryside Services Ltd | Administrative & support | 2016 |
| Oxford Road Launderette Limited | Other services | 1995 |
| O’Briens Hospitality (NE) Ltd | Hospitality | 2025 |
| P & D Laidler Ltd | Professional & scientific | 2008 |
| P & I Design Limited | Information & communication | 1978 |
| P & I Software Limited | Extraterritorial | 1989 |
| P & P Commercial Investments Ltd | Professional & scientific | 2019 |
| P Chapman Electrical Limited | Construction | 2025 |
| P Dolan Inspection Services Ltd | Professional & scientific | 2017 |
| P J a Construction Ltd | Construction | 2019 |
| P K Rhatore Ltd | Administrative & support | 2023 |
| P M Johnson Offshore Limited | Construction | 2012 |
| P S Project Services Limited | Construction | 2015 |
| P Ward Building and Property Services Ltd | Construction | 2024 |
| P&A Auto Repairs Ltd | Wholesale & retail | 2022 |
| P&J Property Investments Ltd | Real estate | 2024 |
| P&L Desserts Ltd | Hospitality | 2026 |
| P&M Global Ltd | Real estate | 2023 |
| P&M Property Rentals Limited | Real estate | 2022 |
| P&R Construction Limited | Construction | 2013 |
| P. Dunn Electrical Services Limited | Construction | 1998 |
| P.C.F. Solutions Limited | Professional & scientific | 2007 |
| P.D.W. Inspection Ltd | Professional & scientific | 2006 |
| P.F.V.A. Ltd | Professional & scientific | 2025 |
| P.I.D.S. Ltd | Construction | 1997 |
| P.M. Cook & Co Ltd | Professional & scientific | 2010 |
| Padel Quarters Group Ltd | Wholesale & retail | 2025 |
| Padel UP (001) Ltd | Arts & recreation | 2025 |
| Padel UP (002) Ltd | Arts & recreation | 2025 |
| Padel UP (003) Ltd | Arts & recreation | 2025 |
| Padel UP (004) Ltd | Wholesale & retail | 2026 |
| Padel UP (005) Ltd | Wholesale & retail | 2026 |
| Padel UP (006) Ltd | Wholesale & retail | 2026 |