| Optic-Comm Civils Ltd | Other services | 2022 |
| Optic-Comm Ltd | Other services | 2017 |
| Optical Jukebox Ltd | Information & communication | 2013 |
| Optiks Solutions UK Ltd. | Information & communication | 2023 |
| Optima Nutrition Ltd | Wholesale & retail | 2025 |
| Optima Scaffold Design Solutions Limited | Construction | 2002 |
| Optima Scaffold Designs LLP | | 2007 |
| Optima Systems Consultancy Limited | Professional & scientific | 2012 |
| Optima Textile Systems Ltd | Manufacturing | 2025 |
| Optimal Calibrations Limited | Professional & scientific | 2024 |
| Optimal Construction SW Limited | Construction | 2024 |
| Optimal Control Solutions Ltd | Professional & scientific | 2024 |
| Optimal Engineering Design Limited | Professional & scientific | 2008 |
| Optimal Portfolio Strategies Limited | Financial services | 2024 |
| Optimal Project Planning Ltd | Professional & scientific | 2023 |
| Optimal Property Management Limited | Real estate | 2018 |
| Optimetrics Limited | Professional & scientific | 2023 |
| Optimido Ltd | Wholesale & retail | 2003 |
| Optimise Destination Management Solutions Limited | Professional & scientific | 2018 |
| Optimised Product Design Ltd | Manufacturing | 2022 |
| Optimist Build and Property Solutions Ltd | Construction | 2026 |
| Optimistik Limited | Health & social care | 2019 |
| Optimistix Limited | Information & communication | 2024 |
| Optimos Consulting Limited | Professional & scientific | 2011 |
| Optimum Access Ltd | Administrative & support | 2015 |
| Optimum B Limited | Health & social care | 2021 |
| Optimum Combined Services Ltd | Construction | 2013 |
| Optimum Direct Ltd | Administrative & support | 2026 |
| Optimum Drywall Systems (South West) Ltd | Construction | 2020 |
| Optimum Drywall Systems Limited | Construction | 2001 |
| Optimum Electrical Services Limited | Extraterritorial | 2011 |
| Optimum Fertility Clinic Ltd | Extraterritorial | 2020 |
| Optimum Fire Stopping Ltd | Construction | 2020 |
| Optimum Group Holdings (South West ) Limited | Construction | 2020 |
| Optimum Mastering Ltd | Arts & recreation | 2003 |
| Optimum Security Systems Ltd | Administrative & support | 1996 |
| Optimus Care Services Limited | Health & social care | 2025 |
| Optimus Chiropractic and Physiotherapy Limited | Health & social care | 2012 |
| Optimus Clinical Consultancy Ltd | Health & social care | 2014 |
| Optimus DB Limited | Construction | 2020 |
| Optimusclips Ltd | Information & communication | 2026 |
| Option O Ltd | Information & communication | 2023 |
| Option to Travel Ltd | Administrative & support | 2006 |
| Options (Bristol) Limited | Arts & recreation | 1999 |
| Options Electrical & Mechanical Services Limited | Construction | 2018 |
| Options Electrical Services Limited | Construction | 2001 |
| Options for Recruitment Limited | Administrative & support | 2021 |
| Optitune Limited | Administrative & support | 2001 |
| Optiweb Solutions Limited | Information & communication | 2017 |
| Optiwork Ltd | Manufacturing | 2016 |
| Optoflo Ltd | Health & social care | 2023 |
| Optrum Ltd | Construction | 2025 |
| Optus Projects Limited | Construction | 2010 |
| Opulence Solutions Ltd | Real estate | 2019 |
| Opulent Mgmt Ltd | Professional & scientific | 2026 |
| Opulyn Ltd | Wholesale & retail | 2026 |
| Opus Enterprises Limited | Administrative & support | 2024 |
| Opus Health Limited | Health & social care | 2008 |
| Opus Onyx Ltd | Information & communication | 2026 |
| Opus Project Management Limited | Construction | 2026 |
| Opus Property Ltd | Construction | 2017 |
| Opus Renewables Ltd | Construction | 2023 |
| Opusapeiro Admin Limited | Information & communication | 2018 |
| Opusapeiro Limited | Administrative & support | 2013 |
| OPW Advisory Services Ltd | Professional & scientific | 2023 |
| OPX Distribution Limited | Transport & logistics | 2021 |
| OPX Logistics Limited | Transport & logistics | 2017 |
| OPX Recruitment Limited | Transport & logistics | 2013 |
| Oqtave Technologies Ltd | Construction | 2026 |
| Oracle Films Limited | Information & communication | 2019 |
| Orahai Limited | Information & communication | 2025 |
| Oral Implantology Limited | Health & social care | 2010 |
| Oramar Store Ltd | Wholesale & retail | 2026 |
| Orange 4X4 Ltd | Wholesale & retail | 2020 |
| Orange Digital Marketing Ltd | Information & communication | 2021 |
| Orange Glow Limited | Professional & scientific | 2024 |
| Orange Kangaroo Ltd | Education | 2018 |
| Orange Orchards Consulting Ltd | Information & communication | 2024 |
| Orange OWL Consultants Ltd | Professional & scientific | 2023 |
| Orange Penguin Properties Ltd | Real estate | 2022 |
| Orange Shed Consulting Ltd | Professional & scientific | 2024 |
| Orange Translations UK Limited | Professional & scientific | 2016 |
| Orangejuice Ltd. | Professional & scientific | 2018 |
| Orangejuicecustoms Ltd | Professional & scientific | 2023 |
| Orangutan Films Limited | Information & communication | 2022 |
| Orau Limited | Real estate | 2021 |
| ORB Mechanical & Electrical Ltd | Construction | 2014 |
| ORB Mechanical Ltd | Construction | 2019 |
| ORB Services Ltd | Construction | 2016 |
| Orbe Entertainment Ltd | Arts & recreation | 2025 |
| Orbimation Technology Limited | Information & communication | 2015 |
| Orbis Allium Ltd | Information & communication | 2011 |
| Orbit Logistics Limited | Transport & logistics | 2026 |
| Orbit Skills Ltd | Administrative & support | 2025 |
| Orbital Electrical South West Ltd | Construction | 2007 |
| Orbital Elements Limited | Manufacturing | 2026 |
| Orbital Steel Ltd | Extraterritorial | 2026 |
| Orbitance Limited | Professional & scientific | 2017 |
| Orbitix Systems Limited | Information & communication | 2025 |
| Orbitz Worldwide (UK) Limited | Professional & scientific | 2007 |