| Omdius Consulting Ltd | Information & communication | 2015 |
| Omega Dynasties Ltd | Wholesale & retail | 2025 |
| Omegaventura Limited | Professional & scientific | 2009 |
| Omkar Sales Limited | Wholesale & retail | 2021 |
| OMW Consulting Ltd | Administrative & support | 2023 |
| ON Demand Building Solutions Limited | Construction | 2026 |
| ON the Move Software Limited | Information & communication | 2012 |
| ON Track Detailing Ltd | Wholesale & retail | 2022 |
| ON Vibe Ltd | Information & communication | 2014 |
| One Call Commercial Services Limited | Other services | 2007 |
| One Exbury Road Management Company Limited | Households | 2025 |
| One Mission MMA Academy Ltd | Health & social care | 2025 |
| One Physiotherapy Limited | Health & social care | 2004 |
| One Thorn Walk Limited | Real estate | 2002 |
| One Voice Consulting Limited | Information & communication | 2012 |
| One&Only Spray Coatings Limited | Construction | 2021 |
| ONE-4-POWER Limited | Manufacturing | 2002 |
| Only Solutions Services Ltd | Administrative & support | 2016 |
| Onset Investments Limited | Real estate | 2018 |
| Onslow Place Management Company Limited | Households | 2018 |
| Onstaff Ltd | Administrative & support | 2024 |
| Onstage Founder I LLP | | 2025 |
| Onstage GP Holdco Ltd | Financial services | 2025 |
| Onstage GP I LLP | | 2025 |
| Onstage I LP | | 2025 |
| Op-Fortitude Ltd | Information & communication | 2018 |
| Opal Black Insurance Services Limited | Financial services | 2022 |
| Opalz Associates Limited | Health & social care | 2009 |
| Open Message Ltd | Information & communication | 2018 |
| Opendeed Residents Management Limited | Households | 1987 |
| Opensystems Architecture Ltd | Professional & scientific | 2012 |
| Operational Acceptance Testing Solutions Ltd | Information & communication | 2019 |
| OPT Fire Protection Limited | Construction | 2024 |
| Optalis Limited | Health & social care | 2011 |
| Optima Trading Group UK Ltd | Energy | 2026 |
| Optimal Fire and Security Limited | Administrative & support | 2014 |
| Optimal Sports Group Ltd | Wholesale & retail | 2024 |
| Optimum SERVICES4U Ltd | Health & social care | 2021 |
| Optimus Events Ltd | Administrative & support | 2025 |
| Optimus Prime Resources Limited | Extraterritorial | 2017 |
| ORA Watch UK Ltd Limited | Other services | 2013 |
| Orange Sage Limited | Professional & scientific | 2014 |
| Orchard Court (Colnbrook) Management Limited | Households | 1992 |
| Orchard Grange (Wokingham) Management Company Limited | Households | 2015 |
| Orderly London Ltd | Construction | 2023 |
| Organised Mind Traning Ltd | Health & social care | 2011 |
| Origin Secured Ltd | Information & communication | 2022 |
| ORM Coffee Solutions Limited | Wholesale & retail | 2024 |
| Osbaldeston Contracting Ltd | Information & communication | 2023 |
| Osborne Court Management (Wokingham) Limited | Households | 1986 |
| Osborne House (Sunningdale) Management Company Limited | Households | 2018 |
| Osborne Management Limited | Households | 1980 |
| Ospec Printing Limited | Manufacturing | 1995 |
| Osprey Construction & Electrical Limited | Construction | 2016 |
| Ostra Ltd | Real estate | 2017 |
| Otech Solutions Ltd | Professional & scientific | 2024 |
| Otium Real Estate Limited | Real estate | 2014 |
| Otkids Ltd. | Health & social care | 2016 |
| Otter Genius Ltd | Information & communication | 2023 |
| OUR Time Properties Ltd | Real estate | 2025 |
| OUT of Your Shell Limited | Administrative & support | 2025 |
| Outdoor Maintenance Company Ltd | Administrative & support | 2022 |
| Ovenu Franchising Limited | Professional & scientific | 1999 |
| Over the Line Brand Solutions Limited | Professional & scientific | 2012 |
| Overbury Design Bureau Limited | Construction | 2022 |
| Overseas Finance and Development Establishment Limited | Real estate | 1984 |
| Ovita Limited | Administrative & support | 2020 |
| Oxford Carers Ltd | Health & social care | 2020 |
| Oxford Computers Limited | Information & communication | 2006 |
| Oxford Road Apartments Limited | Households | 2006 |
| Oxfordshire Hearing Care Ltd | Health & social care | 2021 |
| Ozbiz Limited | Wholesale & retail | 2014 |
| O’Neill Health Economics Limited | Health & social care | 2022 |
| P & T Properties Reading Limited | Real estate | 2022 |
| P Webb Consultancy Ltd | Professional & scientific | 2026 |
| P'S & Tabot Limited | Professional & scientific | 2013 |
| P-Tec Ltd. | Administrative & support | 2018 |
| P.L.T. Marketing Limited | Professional & scientific | 1999 |
| P2P - Person to Person Talking Therapies Ltd | Health & social care | 2020 |
| P3M Independent Limited | Professional & scientific | 2025 |
| PAB Building Ltd | Construction | 2023 |
| Packet Coders Ltd | Education | 2022 |
| Paddock View RTM Company Ltd | Households | 2011 |
| Padel Partners Networking Limited | Administrative & support | 2025 |
| Paideia Education Ltd | Education | 2019 |
| Paktech Consultancy Ltd | Information & communication | 2018 |
| Palatine Oaklands Limited | Households | 2023 |
| Palmers GAS & Heating Services Limited | Construction | 2006 |
| Palmerstone Place RTM Company Ltd | Households | 2015 |
| Palmyra Flavoured Drinks Limited | Wholesale & retail | 2021 |
| Pamela John Dance LLP | | 2025 |
| Panasper Films Limited | Information & communication | 2017 |
| Pangaea Analytics Ltd | Information & communication | 2019 |
| Pangaea Property Holding Ltd | Real estate | 2022 |
| Pantheone Limited | Real estate | 2016 |
| Paper & Purpose Ltd | Professional & scientific | 2025 |
| Paraansh Furnitures Limited | Wholesale & retail | 2026 |
| Parabell Limited | Professional & scientific | 1998 |
| Paradis Publishing Ltd | Information & communication | 2023 |
| Paradise Barz Ltd | Hospitality | 2024 |