| Orka Real Estate Ltd | Construction | 2020 |
| Orla Hill Ltd | Information & communication | 2011 |
| Orlando 2 Limited | Financial services | 2019 |
| Orlando Limited | Arts & recreation | 1987 |
| Orphelins Ltd | Real estate | 2011 |
| Orpheus Music Therapy Services Limited | Health & social care | 1996 |
| Orris&Co. Ltd | Hospitality | 2025 |
| Orsett Business Park Limited | Real estate | 2026 |
| Orthene Chemicals Limited | Manufacturing | 1976 |
| Orthene Holdings Limited | Financial services | 2010 |
| Ortho Mechanics Limited | Other services | 2020 |
| Orthodock Ltd | Information & communication | 2021 |
| Orthopaedics Limited | Health & social care | 2005 |
| Orthopath Limited | Health & social care | 2015 |
| Orthopod Traders Limited | Financial services | 2025 |
| Orto Solis Limited | Construction | 2022 |
| ORU Asana Ltd | Professional & scientific | 2022 |
| ORU Parcel Limited | Hospitality | 2020 |
| ORU Solutions Ltd | Professional & scientific | 2026 |
| Oryx JO Ltd | Real estate | 2018 |
| OS Holdings Group Limited | Financial services | 2022 |
| OS Investments Co. Limited | Real estate | 2022 |
| OS M Ritmos Brasileiros Ltd. | Arts & recreation | 2024 |
| Osaproperties Ltd | Real estate | 2025 |
| Osasil Limited | Real estate | 2021 |
| OSC15 Limited | Health & social care | 2014 |
| Oscano Ltd | Wholesale & retail | 2023 |
| Oshimva Ltd | Wholesale & retail | 2025 |
| Oshrod International UK Ltd | Professional & scientific | 2024 |
| Oshwal Distibutors Limited | Professional & scientific | 1984 |
| OSL Management Limited | Real estate | 2026 |
| Osman &Omar Ltd | Manufacturing | 2013 |
| Ospo NOW Ltd | Information & communication | 2023 |
| OSR Consultancy Services Ltd. | Information & communication | 2014 |
| Osteo.Owais Ltd | Health & social care | 2025 |
| Osteobysonali Ltd | Health & social care | 2026 |
| Ostrander Limited | Professional & scientific | 2024 |
| Ostrander Property Limited | Real estate | 2020 |
| Osumtraders Limited | Wholesale & retail | 2021 |
| Otachieve Limited | Extraterritorial | 2020 |
| Other One Limited | Construction | 2018 |
| Otillie Willow Limited | Professional & scientific | 2016 |
| Otis Jaxon London Ltd | Wholesale & retail | 2021 |
| Otter Trading Limited | Hospitality | 2014 |
| Otto Property Circle Ltd | Households | 2022 |
| Ottoman College Ltd | Wholesale & retail | 2023 |
| OUD Dynasty Limited | Wholesale & retail | 2023 |
| Ouie Ltd | Wholesale & retail | 2017 |
| Oumina Properties Ltd | Real estate | 2024 |
| OUR Indian Food Ltd | Wholesale & retail | 2025 |
| OUR Paint Works Ltd | Construction | 2020 |
| OUR Superior Smile Ltd | Health & social care | 2015 |
| Ouroboros Tattoo Ltd | Arts & recreation | 2020 |
| OURS888 Ltd | Real estate | 2023 |
| OUT of TEN Ltd | Professional & scientific | 2023 |
| Outcomemet Limited | Information & communication | 2024 |
| Outdoor Events Catering Limited | Hospitality | 2023 |
| Outerwear London Ltd | Manufacturing | 2019 |
| Outline AV Limited | Other services | 2019 |
| Outreach Care Support Limited | Health & social care | 2016 |
| Outsmartm Limited | Information & communication | 2013 |
| Outspire Media Limited | Professional & scientific | 2012 |
| OVA Electrical Limited | Construction | 2017 |
| Overhaul Services Ltd | Professional & scientific | 2023 |
| Ovibp Ltd | Transport & logistics | 2018 |
| Ovidiu S RO Ltd | Construction | 2015 |
| Oviproconstruct Ltd | Construction | 2020 |
| OVM Analytics Ltd | Professional & scientific | 2025 |
| Ovrela Ltd | Professional & scientific | 2026 |
| Ovsr Limited | Real estate | 2019 |
| Ovticu Ltd | Transport & logistics | 2016 |
| Ovydavid Limited | Construction | 2015 |
| Owen Housing Solutions Ltd | Professional & scientific | 2015 |
| OWL & Co Limited | Administrative & support | 2013 |
| OWL Events Ltd | Administrative & support | 2026 |
| OWL Investments Ltd | Wholesale & retail | 2024 |
| Owlco Holdings Ltd | Extraterritorial | 2018 |
| Owned by Code Ltd | Information & communication | 2012 |
| OX & Grill Steak House Ltd | Hospitality | 2025 |
| OX Barns Limited | Real estate | 2025 |
| Oxalis Capital Limited | Real estate | 2024 |
| Oxbit Capital 110CP Ltd | Real estate | 2020 |
| Oxbit Capital 122CA Ltd | Real estate | 2026 |
| Oxbit Capital Ltd | Real estate | 2020 |
| Oxbit Ltd | Information & communication | 2012 |
| Oxbridge Learning Ltd | Education | 2025 |
| Oxbridge Semita Ltd | Information & communication | 2022 |
| Oxford Biosensors Limited | Professional & scientific | 2018 |
| Oxford Commerce Limited | Wholesale & retail | 2016 |
| Oxford School of Advanced Studies Limited | Education | 2025 |
| Oxhey Finance Limited | Financial services | 2015 |
| Oxhey Holding Limited | Real estate | 2017 |
| Oxhey Investments Limited | Real estate | 2017 |
| Oxhey Ltd | Real estate | 2021 |
| Oxhey Pharma Limited | Wholesale & retail | 2024 |
| Oxhey Property Limited | Real estate | 2017 |
| Oxhey Property Management Ltd | Real estate | 2013 |
| Oxhey UK Investments Ltd | Real estate | 2021 |
| Oxus Aviation Limited | Transport & logistics | 2012 |
| Oxyfit Impulse Ltd | Wholesale & retail | 2020 |