| Over Community Enterprises Limited | Hospitality | 1995 |
| Over New Road Preschool CIC | Education | 2011 |
| Over Power Franchise Ltd | Administrative & support | 2022 |
| Over Power Northstowe Ltd | Health & social care | 2022 |
| Over the Sea Servicing Ltd | Manufacturing | 2022 |
| Overcote Properties Limited | Real estate | 2017 |
| Overhall Farming LLP | | 2018 |
| Overhall Investments Limited | Financial services | 2020 |
| Overhall Projects Limited | Construction | 2022 |
| Overmorrow Limited | Professional & scientific | 2020 |
| OWA Decoration Materials Co., Ltd | Professional & scientific | 2014 |
| Owega Bloodstock Ltd | Agriculture & fishing | 2024 |
| Owego Inkflow Limited | Information & communication | 2025 |
| Owen Hughes Consulting Limited | Professional & scientific | 2024 |
| Owers Warwick Architects Holdings Ltd | Financial services | 2020 |
| Owlstone Developments Ltd. | Real estate | 2001 |
| Owlstone Limited | Professional & scientific | 2016 |
| Owlstone Medical Limited | Professional & scientific | 2003 |
| Own Boss Ltd | Manufacturing | 2024 |
| Oxbridge Consultancy Services Ltd | Professional & scientific | 2019 |
| Oxbridge Consulting Limited | Professional & scientific | 2001 |
| Oxbridge Cycles Limited | Manufacturing | 2022 |
| Oxbridge Edutech Limited | Education | 2019 |
| Oxbridge Frontier Intelligence Ltd | Financial services | 2026 |
| Oxbridge Health Innovation Limited | Professional & scientific | 2025 |
| Oxbridge Investments Limited | Real estate | 2022 |
| Oxbridge Neural Group LLP | | 2024 |
| Oxbridge Radiology Limited | Health & social care | 2019 |
| Oxbridge Tours Ltd | Education | 2010 |
| Oxcam Global Consulting Limited | Professional & scientific | 2022 |
| Oxcitas Limited | Professional & scientific | 2017 |
| Oxecress Marketing Limited | Hospitality | 2001 |
| Oxford & Bucks Urology Partnership Ltd | Health & social care | 2013 |
| Oxford and Cambridge International Academy of Music and Culture Limited | Education | 2025 |
| Oxford and Cambridge International Assessment Services Limited | Education | 1984 |
| Oxford Distillery Limited | Manufacturing | 2012 |
| Oxford Forensics Limited | Professional & scientific | 2016 |
| Oxford Voyager Venture Capital Ltd | Information & communication | 2020 |
| Oxford West END Capital Limited | Professional & scientific | 2025 |
| Oxhouse Properties Ltd | Real estate | 2024 |
| Oxmed Ltd | Administrative & support | 2006 |
| Oxshare Limited | Financial services | 2025 |
| Oxspace Ltd | Professional & scientific | 2024 |
| Oxynous Ltd | Professional & scientific | 2019 |
| Oyss Research Centre Ltd | Professional & scientific | 2025 |
| Ozar Restaurants Limited | Hospitality | 2019 |
| Ozer & Sons Limited | Construction | 2024 |
| Ozgur Gents Ltd | Other services | 2014 |
| Ozhan Koray Catak Ltd | Other services | 2021 |
| Ozzengin Barbers Limited | Other services | 2020 |
| P & H Solutions Ltd | Administrative & support | 2010 |
| P & K Darke Limited | Professional & scientific | 2024 |
| P a Impey Ltd | Other services | 2012 |
| P Davda Ventures Ltd | Education | 2026 |
| P Harvey and Sons Limited | Construction | 2005 |
| P Hextall Consulting Limited | Professional & scientific | 2014 |
| P I Plastering Ltd | Construction | 2021 |
| P J Brown Plumbing and Heating Limited | Construction | 2004 |
| P J Fencing Contractors Ltd | Construction | 2022 |
| P J Nisbet & Associates Limited | Professional & scientific | 2014 |
| P N H Construction Ltd | Manufacturing | 2013 |
| P S Dean Roofing Contractors Limited | Construction | 2015 |
| P S Fixings Limited | Wholesale & retail | 2001 |
| P S Harlow Plumbing & Heating Limited | Construction | 2017 |
| P S IT Services Ltd | Information & communication | 2026 |
| P S Plumbing Solutions Ltd | Construction | 2015 |
| P S Sandhawalia Ltd | Information & communication | 2025 |
| P Worman Decorating Services Limited | Construction | 2017 |
| P&C Cambridge Limited | Financial services | 2016 |
| P&D Cambridge Limited | Construction | 2021 |
| P&T Munnelly Construction Limited | Construction | 2018 |
| P&T Roofing and Cladding Limited | Construction | 2009 |
| P. X. Farms Limited | Agriculture & fishing | 2003 |
| P. X. Land Limited | Real estate | 2023 |
| P.A.C. Electrical Services Limited | Construction | 1987 |
| P.A.C. Employee Ownership Trustee Ltd | Administrative & support | 2021 |
| P.D. Lawrence & SON Limited | Construction | 1997 |
| P.Meeks (Electrical) Limited | Construction | 1988 |
| P.R.E. Heating Services Ltd | Professional & scientific | 2020 |
| P.S. Property Services Limited | Real estate | 1984 |
| P.X.F. Holdings Limited | Financial services | 2023 |
| P2J2 Technologies Limited | Professional & scientific | 2017 |
| PA Broad Designs Ltd | Professional & scientific | 2024 |
| Paac Consulting Limited | Information & communication | 2024 |
| Paapri Business Technologies UK Ltd | Information & communication | 2019 |
| Pabella Limited | Real estate | 2021 |
| Pablo Nutritional Health Co., Ltd | Manufacturing | 2023 |
| Pace Associates Limited | Professional & scientific | 2010 |
| Pace Aviotecnico Ltd | Manufacturing | 2025 |
| Pace Historics Limited | Arts & recreation | 1995 |
| Pace Micropower Ltd | Professional & scientific | 2013 |
| Paceops Ltd | Professional & scientific | 2018 |
| Pacific International Investment Co., Ltd | Financial services | 2025 |
| Packrobat Automation Ltd | Manufacturing | 2000 |
| Pact Earth Ltd | Manufacturing | 2019 |
| Pact Health Tech Ltd | Information & communication | 2026 |
| Paddington Bidco Limited | Financial services | 2025 |
| Paddington Midco Limited | Financial services | 2025 |
| Paddington Topco Limited | Financial services | 2025 |
| Paddock ST Holdings Ltd | Construction | 1993 |