| OUR Chapters Limited | Information & communication | 2026 |
| OUR Home Accommodations Ltd | Hospitality | 2021 |
| OUR Home Group Ltd | Financial services | 2022 |
| OUR Home Property Company Ltd | Real estate | 2018 |
| OUR Home Short Stays Ltd | Real estate | 2022 |
| OUR Ideas Limited | Wholesale & retail | 2004 |
| OUR Mish CIC | Health & social care | 2025 |
| OUT Point Media Ltd | Administrative & support | 2019 |
| Outdoor Learning Alliance Community Interest Company | Education | 2025 |
| Outdoor Tribe CIC | Education | 2016 |
| Outlines Media Group Ltd | Information & communication | 2022 |
| Outrex Prisma Ltd | Wholesale & retail | 2025 |
| Outside Inspired Limited | Other services | 2021 |
| Outsourced Accounting Limited | Professional & scientific | 2002 |
| Oval Park Construction Limited | Construction | 2009 |
| Overmind Technology Ltd | Information & communication | 2025 |
| Overnet Data Holdings Ltd | Financial services | 2022 |
| Overnet Data Ltd | Information & communication | 2007 |
| Overnet Data Management Ltd | Information & communication | 2010 |
| Overstone Chauffeur Services Ltd | Other services | 2016 |
| Overstone Construction Limited | Extraterritorial | 2006 |
| Overstone Gate Residents Management Company Limited | Households | 2020 |
| Overstone Heights Management Limited | Households | 2005 |
| Overstone Holdings Limited | Financial services | 2016 |
| Overstone House Residents Company Limited | Hospitality | 1985 |
| Overstone Motors (1981) Limited | | 1981 |
| Overstone Park Management Limited | Households | 1980 |
| Overstone Park School Ltd | Education | 2010 |
| Overstone Road 78 Management Company Limited | Households | 2019 |
| Overtimehosting Ltd | Information & communication | 2023 |
| Overwatch Risk Management Solutions Limited | Professional & scientific | 2024 |
| Ovidiu Andrei Neagu Ltd | Transport & logistics | 2019 |
| Ovidiu Balan Ltd | Transport & logistics | 2018 |
| Ovidiu Patrau Ltd | Construction | 2015 |
| Ovidiu Vlad Limited | Transport & logistics | 2019 |
| Ovyary Limited | Transport & logistics | 2015 |
| OW10 Limited | Arts & recreation | 2014 |
| Owais Hussain Ltd | Health & social care | 2022 |
| Owen & Langley Limited | Hospitality | 2023 |
| Owerre-Nkworji Development Foundation | Other services | 2011 |
| OWL Autos Limited | Wholesale & retail | 2013 |
| OWL Property Group Limited | Real estate | 2017 |
| Owlgeek Ltd | Information & communication | 2022 |
| Owls Nest Nursery Limited | Health & social care | 2019 |
| Own Merit CIC | Hospitality | 2021 |
| Own Your Craft Ltd | Arts & recreation | 2023 |
| Ownyourhealth Ltd | Wholesale & retail | 2025 |
| Oxalis Engineering Ltd | Manufacturing | 2020 |
| Oxbridge Futures Limited | Education | 2015 |
| Oxbridge Group Ltd | Education | 2013 |
| Oxel Property Limited | Real estate | 2026 |
| Oxford Guardians Limited | Public administration | 2009 |
| Oxford Property Investments Ltd | Financial services | 2015 |
| Oxford Street Therapy Centre Ltd | Other services | 2013 |
| Oxon Fabrications Limited | Construction | 2016 |
| OYC Studio Ltd | Professional & scientific | 2023 |
| Oyet Limited | Health & social care | 2025 |
| Oyeyemi.Ogungbure Healthcare Limited | Public administration | 2022 |
| Oylr Limited | Professional & scientific | 2022 |
| Oystashell IP Limited | Information & communication | 2020 |
| Oystashell Limited | Information & communication | 2020 |
| Oystershell Limited | Professional & scientific | 1999 |
| Oz/Es Ltd | Hospitality | 2023 |
| Ozel Catering Ltd | Hospitality | 2021 |
| Ozlati & Co Ltd | Wholesale & retail | 2012 |
| Ozzy Electrical Installations Ltd | Construction | 2023 |
| O’Connor and Co Holdings Limited | Financial services | 2022 |
| P & a Taylor Ltd | Construction | 2005 |
| P & D Enterprise Limited | Real estate | 2022 |
| P & J Interiors Ltd | Construction | 2021 |
| P & M Building & Carpentry Services Limited | Construction | 2006 |
| P & R Burbage Limited | Agriculture & fishing | 2007 |
| P & S Plant and Construction Limited | Construction | 2015 |
| P & W Electrical Limited | Energy | 2013 |
| P a Cassidy (Mechanical Services) Limited | Construction | 1998 |
| P and E Contractors Ltd | Administrative & support | 2021 |
| P B Consultants Ltd | Professional & scientific | 2022 |
| P Bebel Ltd | Transport & logistics | 2018 |
| P H Hughes Consulting Limited | Professional & scientific | 2017 |
| P Harvey Heating Limited | Construction | 2017 |
| P J B Glass Group Limited | Manufacturing | 2006 |
| P J Dolman Landscapes Limited | Real estate | 2016 |
| P J H Marketing Limited | Wholesale & retail | 2006 |
| P J Hodge & Sons Limited | Wholesale & retail | 2005 |
| P J Townley Carpentry and Kitchens Limited | Manufacturing | 2025 |
| P L Marriott Consulting Limited | Professional & scientific | 2021 |
| P L Marriott Estates Limited | Construction | 2020 |
| P Lyman Construction Ltd | Construction | 2010 |
| P M B Investments Limited | Real estate | 2016 |
| P M Rowlands Heating Engineers Ltd | Construction | 2012 |
| P N B Maison Limited | Real estate | 2018 |
| P N Motors Ltd | Wholesale & retail | 2024 |
| P O'Reilly Limited | Construction | 2017 |
| P Paul Construction Limited | Construction | 2022 |
| P R Contractors and Sons (Northants) Ltd | Administrative & support | 2013 |
| P Skiba Transport Ltd | Transport & logistics | 2016 |
| P Sula Construction Ltd | Construction | 2021 |
| P W & G E Hinton Limited | Agriculture & fishing | 1999 |
| P W Curtis Limited | Transport & logistics | 2008 |
| P W Vehicle Refinishers Ltd | Wholesale & retail | 2025 |