| Origin Products Limited | Professional & scientific | 1980 |
| Original Taste of Pakistan Slough Ltd | Hospitality | 2026 |
| Orions Face Studio Ltd | Information & communication | 2025 |
| Orivaana Ltd | Wholesale & retail | 2026 |
| Orlando Estates Ltd | Real estate | 2020 |
| Orlux Ltd | Health & social care | 2026 |
| ORO Rosso Limited | Wholesale & retail | 2024 |
| Orpheus Arts Limited | Arts & recreation | 2014 |
| Orrell Residential Ltd | Real estate | 2025 |
| Orthoclinic Battersea Limited | Health & social care | 2007 |
| Orthonics Limited | Professional & scientific | 2009 |
| Orthoxcel Ltd | Education | 2025 |
| Ortiz Global Commodities Ltd | Wholesale & retail | 2017 |
| Orvanta Health Ltd | Health & social care | 2026 |
| Oryx Hotels Ltd | Hospitality | 2025 |
| Oryx Retail Limited | Wholesale & retail | 2016 |
| OS Sales Consulting Ltd | Information & communication | 2024 |
| OSA Digital Services Ltd | Information & communication | 2025 |
| OSA Services UK Ltd | Construction | 2017 |
| Osborne Flats Management (Slough) Limited | Households | 1980 |
| Oshakati Island Limited | Households | 2024 |
| Osidor Limited | Health & social care | 2018 |
| Osmarix Limited | Construction | 2025 |
| Osoo Solutions Ltd | Information & communication | 2015 |
| OSR 247 Ltd | Transport & logistics | 2024 |
| Osteria Restaurants Ltd | Hospitality | 2017 |
| Oswestry (T2) Hairdressing Limited | Other services | 2018 |
| OT Smiles Limited | Health & social care | 2024 |
| Otek Digital Ltd | Information & communication | 2022 |
| OTM Properties Ltd | Real estate | 2022 |
| Ottscars Limited Limited | Transport & logistics | 2025 |
| Oubi Ltd | Wholesale & retail | 2026 |
| OUD House Ltd | Wholesale & retail | 2025 |
| Oudaari Limited | Wholesale & retail | 2025 |
| Oulis Construction Ltd | Construction | 2017 |
| OUR Home Your Home Ltd | Hospitality | 2024 |
| OUR Trail Ltd | Hospitality | 2013 |
| Oura Apparel Limited | Wholesale & retail | 2025 |
| Ouranos Properties Limited | Real estate | 2022 |
| Outlet Noon Limited | Wholesale & retail | 2024 |
| Outreach Care and Staffing Ltd | Administrative & support | 2019 |
| Outreach Entertainment Ltd | Administrative & support | 2022 |
| Outreach Recruitment Services Ltd | Health & social care | 2018 |
| Outsource Cleaning Ltd | Administrative & support | 2007 |
| Outsource Xperts Ltd | Wholesale & retail | 2016 |
| Outstaff Solutions Limited | Administrative & support | 2026 |
| Outvard Limited | Construction | 1982 |
| OVA Tiles Limited | Wholesale & retail | 2019 |
| Ovations Properties Ltd | Real estate | 2020 |
| Ovations Umbrella Limited | Administrative & support | 2020 |
| Overpowerfulbureaucratsshouldbe Limited | Information & communication | 2010 |
| Overseas Pakistani Power Awards Oppa Ltd | Hospitality | 2025 |
| Ovi-Ewi-Insulation Ltd | Construction | 2024 |
| OVO Global Ltd | Financial services | 2024 |
| Ovrure Marketing Limited | Wholesale & retail | 2025 |
| Owen Winn Design Ltd | Professional & scientific | 2023 |
| Own Path Athletics Ltd | Wholesale & retail | 2026 |
| Owners United Ltd | Construction | 2021 |
| Oxford & Beyond Ltd | Education | 2025 |
| Oxford Biochar Ltd | Manufacturing | 2024 |
| Oxford Chamber of Commerce Limited | Other services | 2011 |
| Oxford Homes Ltd | Real estate | 2026 |
| Oxford House (Slough) Limited | Construction | 2020 |
| Oxford House Care Limited | Other services | 1996 |
| Oxford Street Properties Limited | Real estate | 2018 |
| Oxford Training Centre Ltd | Education | 2024 |
| Oxfordshire Chamber of Commerce Limited | Other services | 2011 |
| Oxon Services Management Ltd | Construction | 2019 |
| OXY Marketing Limited | Administrative & support | 2026 |
| Ozin Ltd | Health & social care | 2025 |
| Ozoigbo Ltd | Health & social care | 2024 |
| Ozomark Ltd | Information & communication | 2026 |
| Ozon Ltd | Health & social care | 2014 |
| Ozur Logistics Limited | Transport & logistics | 2026 |
| O’Brien Automotive Ltd | Transport & logistics | 2024 |
| P & G Accident Repairs Ltd | Wholesale & retail | 2019 |
| P & J Optic-Kleer Limited | Wholesale & retail | 2012 |
| P & M Boyce Limited | Water & waste | 2006 |
| P and S Plumbing Heating Limited | Construction | 2022 |
| P E Millat Ltd | Information & communication | 2008 |
| P Josan Builders Limited | Construction | 2024 |
| P K Prop Invest Limited | Real estate | 2019 |
| P Olives Food Ltd | Hospitality | 2026 |
| P P Wood Limited | Construction | 2002 |
| P S Crestin Limited | Health & social care | 2024 |
| P S Dhanoa Transport Ltd | Transport & logistics | 2026 |
| P Saini Construction Ltd | Construction | 2016 |
| P&B Interiors Ltd | Construction | 2024 |
| P&M Home London Ltd | Real estate | 2025 |
| P&M Investment (London) Limited | Real estate | 2021 |
| P&N Groundworks Ltd | Construction | 2021 |
| P&R Projects Limited | Construction | 2024 |
| P.A.C.K Travel Ltd | Administrative & support | 2024 |
| P.D. Motors Limited | Wholesale & retail | 2001 |
| P.K. Properties (UK) Ltd | Real estate | 2000 |
| P.M.O. Plumbing & Heating Solutions Ltd | Construction | 2011 |
| P3 Autos Limited | Wholesale & retail | 2024 |
| P3 Trading Ltd | Wholesale & retail | 2017 |
| P5K Consulting Ltd | Information & communication | 2015 |
| PA Labs Ltd | Professional & scientific | 2026 |