| Omega Healthcare Solutions Ltd | Health & social care | 2020 |
| Omev Limited | Professional & scientific | 2024 |
| Omne Agency Limited | Professional & scientific | 2001 |
| Omne Bidco Limited | Financial services | 2024 |
| Omne Topco Limited | Financial services | 2024 |
| Omni Money Solutions Limited | Information & communication | 2019 |
| Omni People Limited | Health & social care | 2014 |
| Omni-Channel Marketing Ltd | Professional & scientific | 2024 |
| Omniavincit Holding Ltd | Real estate | 2025 |
| Omonosun Investments Ltd | Public administration | 2022 |
| OMT Amusements Ltd | Arts & recreation | 2025 |
| ON Four Wheels Limited | Wholesale & retail | 2025 |
| ON PAR Interiors Limited | Professional & scientific | 2022 |
| ON Property Partners Ltd | Real estate | 2025 |
| ON SET Rigging Solutions Limited | Professional & scientific | 2025 |
| ON Site Associates Limited | Construction | 2019 |
| ON the Marc Carpentry and Joinery Ltd | Manufacturing | 2025 |
| ON Track Education Services Limited | Education | 2005 |
| ON Track to CEO Ltd | Information & communication | 2026 |
| On-Call Caring Ltd | Administrative & support | 2022 |
| On-Line Roadmarking Limited | Construction | 2015 |
| ONA Services Ltd | Administrative & support | 2021 |
| Once Upon a Pixel Ltd | Professional & scientific | 2022 |
| One Albany Close Ltd | Real estate | 2018 |
| One Approach Road Freehold Limited | Households | 2023 |
| One Cargo Hub Limited | Transport & logistics | 2024 |
| One for Road Ltd | Hospitality | 2024 |
| One Group Developments Ltd | Real estate | 2025 |
| One Group Services Ltd | Administrative & support | 2010 |
| One JM Limited | Health & social care | 2015 |
| One MEP Ltd | Construction | 2022 |
| One Pangolin Limited | Professional & scientific | 2024 |
| One Podiatry Ltd | Health & social care | 2025 |
| One Shop Roofing Merchants Limited | Wholesale & retail | 2017 |
| One Stop Breaker Ltd | Other services | 2014 |
| One Strategic Communication Limited | Professional & scientific | 2000 |
| One Twenty Grove Limited | Professional & scientific | 2015 |
| One Two Sports Consultancy Ltd | Education | 2024 |
| One Water Please Limited | Wholesale & retail | 2019 |
| One Wavelength Ltd | Information & communication | 2011 |
| One World Engineering Ltd | Other services | 2014 |
| One Zero Publishing Limited | Information & communication | 2011 |
| ONE2ONE Cars Ltd | Transport & logistics | 2015 |
| ONE51 ES Metals (UK) Limited | Financial services | 2008 |
| Oneil Plumbing & Heating Ltd. | Construction | 2016 |
| ONF Online Ltd | Wholesale & retail | 2021 |
| Onicateus Limited | Professional & scientific | 2023 |
| Online Playgrounds Limited | Professional & scientific | 2010 |
| Only for the Glory Ltd | Information & communication | 2013 |
| Onlylobo Ltd | Professional & scientific | 2018 |
| Onside Sales Limited | Administrative & support | 2017 |
| Onsite Building Control Ltd | Construction | 2000 |
| Onwards & Upwards Ventures Ltd | Real estate | 2023 |
| Onyx Corporation Ltd | Hospitality | 2013 |
| OOC Marketing Limited | Other services | 2014 |
| OP Builders Limited | Manufacturing | 2025 |
| Opait Solutions Limited | Information & communication | 2012 |
| Opal Xena Ltd | Hospitality | 2025 |
| Opel Ltd | Wholesale & retail | 2025 |
| Open House Estate Agents Bedford Ltd | Real estate | 2013 |
| Open House HMO Limited | Real estate | 2017 |
| Open Sight Ltd | Information & communication | 2012 |
| Openui Ltd | Information & communication | 2024 |
| Opera Omnia Productions Limited | Arts & recreation | 2016 |
| Optes Services Limited | Wholesale & retail | 2022 |
| Optiems Limited | Information & communication | 2024 |
| Optimal Health Doctor Ltd | Health & social care | 2025 |
| Optimal Solution Services Limited | Administrative & support | 2024 |
| Optimis Consulting Limited | Professional & scientific | 2012 |
| Optimis Estates Limited | Professional & scientific | 2015 |
| Optimis Group Limited | Financial services | 2016 |
| Optimum Homeimprovements Ltd | Administrative & support | 2017 |
| Optimum Motor Contracts Ltd | Wholesale & retail | 2023 |
| Optivest Properties Limited | Real estate | 2023 |
| Optix Security Limited | Administrative & support | 2013 |
| Opul Aviation Limited | Transport & logistics | 2025 |
| Opulent Home Kitchen Collections Ltd | Manufacturing | 2024 |
| Orange Frog Graphics Ltd | Wholesale & retail | 2017 |
| Orange Glow Energy Limited | Construction | 2010 |
| Orange Peel Intellectual Limited | Information & communication | 2012 |
| Orange Rose Hospitality Ltd | Hospitality | 2023 |
| Orange Tulip Hospitality Ltd | Hospitality | 2023 |
| Orbis Design Ltd | Professional & scientific | 2020 |
| Orbitacx Limited | Professional & scientific | 2017 |
| Orchard Castle Trading Limited | Hospitality | 2012 |
| Orchard Dynamics Ltd | Construction | 2024 |
| Orchard END Farm Ltd | Agriculture & fishing | 2024 |
| Orchard Fruit Co. UK Limited | Wholesale & retail | 2018 |
| Orchard Home Surveys Ltd | Professional & scientific | 2023 |
| Orchid Fields (Phase 2) Management Company Limited | Households | 2016 |
| Orchid Homecare Ltd | Health & social care | 2015 |
| Ordentum Ltd | Information & communication | 2026 |
| Order 2 EAT Limited | Hospitality | 2017 |
| Order Systems Limited | Wholesale & retail | 2017 |
| Ordinary Toucan Ltd. | Information & communication | 2014 |
| Organic the Best Ltd | Wholesale & retail | 2019 |
| Organica Vita Ltd | Manufacturing | 2015 |
| Orgev Laboratories Ltd | Health & social care | 2011 |
| Oriental Cuisine Bedford Ltd | Hospitality | 2023 |
| Origin 8 Consultancy Limited | Extraterritorial | 2018 |