| Otovo Limited | Wholesale & retail | 2022 |
| OTQ Enterprises Ltd | Extraterritorial | 2015 |
| Otraps Real Business Solutions Ltd | Real estate | 2013 |
| Ottman Limited | Professional & scientific | 2005 |
| Oufali Ltd. | Wholesale & retail | 2025 |
| OUR Daily Thread Limited | Administrative & support | 2017 |
| OUR Flats Ltd | Real estate | 2026 |
| Ours Home Asset Management Limited | Real estate | 2015 |
| Ouse Valley Automotive Ltd | Wholesale & retail | 2025 |
| Oustrup Trust UK Limited | Professional & scientific | 2018 |
| OUT of Town Shops Limited | Other services | 2013 |
| Out&Out Natures Intention Ltd | Wholesale & retail | 2026 |
| Outbooks Tech Ltd | Information & communication | 2023 |
| Outcome Focus Limited | Administrative & support | 2009 |
| Outdoor & Living Collective Ltd | Administrative & support | 2016 |
| Outdoor Play and Learning (Opal) Creative Limited | Education | 2018 |
| Outer Join Limited | Information & communication | 2022 |
| Outer-Space Developments Ltd | Construction | 2024 |
| Outlier Trading Limited | Administrative & support | 2015 |
| Outofthebox Solutions Limited | Transport & logistics | 2016 |
| Output Generator Limited | Financial services | 2021 |
| Outreach Cadence Limited | Information & communication | 2023 |
| Outsource-Fd Limited | Professional & scientific | 1999 |
| Outta Time Studio Ltd | Wholesale & retail | 2025 |
| Ouzel Island Resident Management Company Limited | Households | 2015 |
| Over the Hedge Drones Ltd | Professional & scientific | 2025 |
| Over the Skye Daycare Ltd | Health & social care | 2026 |
| Overgate Stone Cutting Shaping Ltd | Manufacturing | 2022 |
| Overkill Performance UK Ltd | Wholesale & retail | 2021 |
| Overland Properties Limited | Real estate | 2019 |
| Overlot Solutions Limited | Wholesale & retail | 2000 |
| Overthink Limited | Professional & scientific | 2021 |
| Ovidrive UK Limited | Information & communication | 2021 |
| Ovispeed Transport Ltd | Transport & logistics | 2016 |
| OVO Electrical Ltd | Construction | 2022 |
| Owen James Developments Limited | Construction | 2018 |
| Owens Motosports Ltd | Manufacturing | 2023 |
| Own Projects Limited | Construction | 2018 |
| Owusu & Co. Properties Ltd | Real estate | 2025 |
| Oxbow Farms UK Ltd | Agriculture & fishing | 2019 |
| Oxbridge Graduate Studies Ltd | Education | 2015 |
| Oxbridge Ltd | Education | 2015 |
| Oxford Dental Hub Limited | Health & social care | 2025 |
| Oxford Dream Academy Ltd | Education | 2018 |
| Oxford EMI Certification Limited | Professional & scientific | 2018 |
| Oxford EMI Consulting Limited | Extraterritorial | 2018 |
| Oxford EMI Limited | Professional & scientific | 2017 |
| Oxford EMI Research Limited | Professional & scientific | 2018 |
| Oxford EMI Training Limited | Professional & scientific | 2018 |
| Oxford Horizons Ltd | Professional & scientific | 2025 |
| Oxford Medical Enterprises Ltd | Health & social care | 2018 |
| Oxford Professional Academy Ltd | Professional & scientific | 2019 |
| Oxford Quantum Systems Dynamics Ltd | Professional & scientific | 2014 |
| Oxford Research International (UK) Ltd | Professional & scientific | 1996 |
| Oxford Research International Limited | Professional & scientific | 1997 |
| Oxford Secured Company Ltd | Wholesale & retail | 2012 |
| OXG Ltd | Construction | 2016 |
| Oxir Ltd | Wholesale & retail | 2021 |
| Oxley Fish & Chips Limited | Hospitality | 2024 |
| Oxley Park Academy Trust | Education | 2011 |
| Oxley Park Dental Practice LLP | | 2008 |
| Oxley Park Veterinary Services Limited | Professional & scientific | 2010 |
| Oxley Totally Kids Ltd | Health & social care | 2026 |
| Oxon Advisory Limited | Professional & scientific | 2023 |
| Oxspines Osteopathy Ltd | Health & social care | 2025 |
| Oxygen Technologies Limited | Administrative & support | 2016 |
| Oynb Limited | Other services | 2015 |
| Oyster Flame Ltd | Professional & scientific | 2011 |
| Ozcan Investment Limited | Real estate | 2022 |
| Ozkutan & Murati Limited | Real estate | 2005 |
| Ozone Technical Facilities Ltd | Construction | 2025 |
| OZY Travels Limited | Administrative & support | 2024 |
| Ozzy's Ansin Turkish Barbers Ltd | Other services | 2023 |
| Ozzy's Express Ltd | Hospitality | 2025 |
| OZZY378PROPERTY Ltd | Real estate | 2025 |
| O’Connor Plumbing and Heating Ltd | Wholesale & retail | 2025 |
| O’S Creations Ltd | Wholesale & retail | 2024 |
| P & a Software Solutions (UK) Limited | Information & communication | 2001 |
| P & a Trading Ltd | Other services | 2006 |
| P & G Homes Ltd | Real estate | 2017 |
| P & G Infotech Ltd | Information & communication | 2017 |
| P & J Services (Milton Keynes) Limited | Administrative & support | 2004 |
| P & MJ Property Holdings Limited | Real estate | 2025 |
| P & S Kitchen Installations Ltd | Administrative & support | 2017 |
| P & U Property Investments Limited | Real estate | 2018 |
| P & Y Tuition & Support Services Ltd | Education | 2015 |
| P & Z Projects Ltd | Professional & scientific | 2023 |
| P a Steeds Consulting Limited | Professional & scientific | 2021 |
| P and R Specialist Contractors Limited | Construction | 2022 |
| P Berry Trading Ltd | Wholesale & retail | 2021 |
| P Booden Consultancy Ltd | Professional & scientific | 2025 |
| P Eldred & Associates Ltd | Professional & scientific | 2016 |
| P F I Systems Limited | Manufacturing | 1992 |
| P J Barber Flooring Limited | Administrative & support | 2000 |
| P J M Holdings Limited | Financial services | 1992 |
| P M C Marketing Ltd | Wholesale & retail | 1999 |
| P M Walsh (Plant Hire) Ltd | Construction | 2024 |
| P Moriarty Construction Limited | Construction | 2020 |
| P P Tours Limited | Real estate | 2021 |
| P R Potential Limited | Financial services | 2013 |