| OSQ Design Ltd | Administrative & support | 2019 |
| Ostec Solutions Ltd | Extraterritorial | 2014 |
| Otaheite Limited | Information & communication | 2015 |
| OTB Consulting Services Ltd | Professional & scientific | 2017 |
| OTC Productions Limited | Information & communication | 2008 |
| OTC2U Limited | Wholesale & retail | 2019 |
| Otesa Occupational Therapy Services Limited | Health & social care | 2022 |
| Otherstuff Limited | Manufacturing | 2017 |
| Otterspool Van Ltd | Hospitality | 2019 |
| Otto Green Solutions Ltd | Professional & scientific | 2023 |
| OU Three One Ltd | Information & communication | 2021 |
| Oudia London Ltd | Wholesale & retail | 2022 |
| OUR Brothers Cafe Ltd | Hospitality | 2023 |
| OUR Brothers Mini Market Ltd | Wholesale & retail | 2024 |
| OUR Brother’S Ltd | Hospitality | 2023 |
| OUT of Ashes CIC | Education | 2025 |
| OUT of the Box Property Solutions Limited | Households | 2017 |
| OUT Tides Limited | Information & communication | 2015 |
| Outlift Ltd | Wholesale & retail | 2025 |
| Outperform Ventures Limited | Administrative & support | 2020 |
| Outwoods Consultant Ltd | Professional & scientific | 2020 |
| Oval Acoustics Limited | Professional & scientific | 2024 |
| Oval Venues Limited | Hospitality | 2013 |
| Ovarian Ltd | Construction | 2026 |
| Over the NET Limited | Arts & recreation | 2025 |
| Overance LLP | | 2023 |
| Overdene House Freehold Co Limited | Households | 2018 |
| Overdene House RTM Company Limited | Households | 2011 |
| Overseas Immigration Ltd | Other services | 2021 |
| Overseas Services Ltd | Administrative & support | 2017 |
| Overtrees Limited | Households | 2002 |
| Overwillow Ltd | Information & communication | 2014 |
| Ovsos Ltd | Education | 2024 |
| Owa's Venture Limited | Health & social care | 2014 |
| OWL + Lark Limited | Wholesale & retail | 2020 |
| Owlaway Limited | Construction | 2025 |
| Ownisol Limited | Information & communication | 2019 |
| OX Properties Limited | Real estate | 2021 |
| Oxane Partners Limited | Professional & scientific | 2013 |
| Oxford Content and Communications Ltd | Information & communication | 2020 |
| Oxford Flight School Ltd | Education | 2020 |
| Oxford Pubs Limited | Hospitality | 2025 |
| Oxford Study Circle Ltd | Education | 2015 |
| Oxgrove Consulting Ltd | Professional & scientific | 2018 |
| Oxhey Car Sales Ltd | Wholesale & retail | 2025 |
| Oxhey Food Nation Limited | Hospitality | 2024 |
| Oxhey Trading Ltd | Wholesale & retail | 2025 |
| Oxheypharm Ltd | Wholesale & retail | 2017 |
| Oxhurst Limited | Professional & scientific | 2026 |
| Oxley Scaffolding Ltd | Construction | 2025 |
| Oxon IT Development Ltd | Information & communication | 2019 |
| Oxsparks Heating and Electrical Limited | Construction | 2019 |
| Oxygen Consultancy Services Limited | Administrative & support | 2015 |
| Oyeboxa Ltd | Arts & recreation | 2021 |
| OZ Express Sandwich Ltd | Hospitality | 2025 |
| OZ Mediterranean Ltd | Hospitality | 2024 |
| OZA Wellbeing Ltd | Other services | 2025 |
| Ozbrand Limited | Construction | 2024 |
| OZE Sushi Limited Limited | Hospitality | 2020 |
| OZH3 Ltd | Real estate | 2021 |
| Ozone Property Management Limited | Real estate | 2017 |
| P & D Consultancy Limited | Professional & scientific | 2023 |
| P & D Hospitality Limited | Hospitality | 2014 |
| P & D Property Management Ltd | Real estate | 2020 |
| P & G Supplies Limited | Wholesale & retail | 1998 |
| P & J Pharma Holdings Ltd | Wholesale & retail | 2022 |
| P & L Retails Ltd | Wholesale & retail | 2003 |
| P & R Roofing (Kent) Limited | Administrative & support | 2010 |
| P a D Propipes Services Limited | Construction | 2025 |
| P and F Sawko Ltd | Professional & scientific | 2025 |
| P Anderson Properties Limited | Real estate | 2003 |
| P B Donoghue (Waste Management) Limited | Water & waste | 2011 |
| P B Donoghue Construction (Watford) Limited | Water & waste | 2015 |
| P Brown Construction Ltd | Construction | 2021 |
| P Carey Services Limited | Construction | 2008 |
| P D Motors & Haulage Limited | Transport & logistics | 2012 |
| P Diamonds Fashion Ltd | Wholesale & retail | 2020 |
| P I B Contractors Ltd | Construction | 2004 |
| P M Hobbs Building Services Limited | Construction | 2012 |
| P Mcnulty Limited | Professional & scientific | 2016 |
| P Pandya Limited | Health & social care | 2015 |
| P R Business Ltd | Wholesale & retail | 2015 |
| P R Business Solutions Ltd | Professional & scientific | 2013 |
| P W Civil Engineering Ltd | Construction | 2016 |
| P&B Finance Limited | Transport & logistics | 2025 |
| P&B Motors Ltd | Wholesale & retail | 2026 |
| P&C Consulting Limited | Professional & scientific | 2018 |
| P&C Media Sales Limited | Wholesale & retail | 2013 |
| P&M Retail Enterprise Ltd | Wholesale & retail | 2026 |
| P&P Global Services Ltd | Construction | 2014 |
| P&S Marine Services Limited | Manufacturing | 2021 |
| P. B. Donoghue (Construction) Limited | Transport & logistics | 1984 |
| P. J. Heating and Plumbing Limited | Construction | 2008 |
| P.A. Underwood Ltd | Information & communication | 1984 |
| P.B. Donoghue (Skip Hire) Limited | Professional & scientific | 1984 |
| P.H.R. Ltd | Manufacturing | 2001 |
| P.J. Herton Limited | Professional & scientific | 2015 |
| P.Joseph Design and Build Limited | Construction | 2020 |
| P.T.N. Limited | Real estate | 1960 |
| P1 Specialist Cars Ltd | Wholesale & retail | 2024 |