| Oliver Harrison Ltd | Professional & scientific | 2019 |
| Olivers Construction Services Limited | Construction | 2022 |
| Olivia's Cat Sitting Limited | Other services | 2025 |
| Oliviaveronicaroberts Ltd | Professional & scientific | 2024 |
| Olivo Property Group Ltd | Real estate | 2024 |
| Ollerton Dental Limited | Health & social care | 2021 |
| Ollerton Investments Ltd | Real estate | 2025 |
| Olliee's Nest Limited | Wholesale & retail | 2015 |
| Ollybeaut Hair Salon Ltd | Other services | 2025 |
| Olsen Actuators Ltd | Manufacturing | 2018 |
| Olsen Engineering Group Ltd | Professional & scientific | 2014 |
| Olsen Engineering UK Ltd | Professional & scientific | 2004 |
| Olsen Subsea Controls Ltd. | Manufacturing | 2010 |
| OLT Ltd | Health & social care | 2019 |
| Omala Limited | Other services | 2019 |
| Omani Consulting Ltd | Professional & scientific | 2015 |
| Omarvision Ltd | Health & social care | 2023 |
| Omega Access Holdings Limited | Other services | 2014 |
| Omega Access North Limited | Administrative & support | 2005 |
| Omega Holding Group Ltd | Financial services | 2024 |
| Omega Multi-Academy Trust | Education | 2012 |
| Omega Site Services Limited | Construction | 2002 |
| Omerevin Ltd | Hospitality | 2026 |
| OMG Holdings Limited | Professional & scientific | 2025 |
| OMG Supplements Ltd | Wholesale & retail | 2026 |
| OMM Healthcare Ltd | Health & social care | 2019 |
| Omni Design Group Limited | Manufacturing | 2019 |
| Omniaone Ltd | Wholesale & retail | 2018 |
| Omnicell Limited | Wholesale & retail | 2002 |
| Omnigate Digital Ltd | Information & communication | 2026 |
| Omnipotent Construction Ltd | Construction | 2025 |
| Omnis Engineering Limited | Manufacturing | 2011 |
| Omnitrim Ltd | Professional & scientific | 2026 |
| Omsai Engineering Limited | Administrative & support | 2013 |
| ON Air Media Limited | Information & communication | 2014 |
| ON Business Support Limited | Professional & scientific | 2021 |
| ON Padel Flint Ltd | Arts & recreation | 2026 |
| ON Padel Group Ltd | Arts & recreation | 2025 |
| ON Padel Ltd | Arts & recreation | 2024 |
| ON the Internet Ltd | Information & communication | 2009 |
| ON the Wall Construction Limited | Construction | 2019 |
| Onaise Management Ltd | Wholesale & retail | 2019 |
| Oncad Ltd | Professional & scientific | 2022 |
| One AM Consulting Limited | Administrative & support | 2026 |
| One Breath Leadership UK Limited | Information & communication | 2026 |
| One Chester Road Ltd | Administrative & support | 2007 |
| One Click Telecom Ltd | Information & communication | 2023 |
| One Community Trust | Education | 2019 |
| One Compliance Cyber Ltd | Information & communication | 2014 |
| One Cost Limited | Administrative & support | 2004 |
| One Design & Print Ltd | Manufacturing | 2016 |
| One Dynamics Group Limited | Information & communication | 2025 |
| One Four Properties Ltd | Real estate | 2023 |
| One Home Holdings UK Ltd | Financial services | 2023 |
| One Home Property UK Ltd | Real estate | 2023 |
| One Home UK Care Ltd | Health & social care | 2023 |
| One IT Limited | Information & communication | 2003 |
| One Link Digital Limited | Professional & scientific | 2018 |
| One Resourcing Solutions Limited | Administrative & support | 2014 |
| One Staff Recruitment Ltd | Administrative & support | 2019 |
| One Stop Idris Ltd | Information & communication | 2023 |
| One Three Three Property Group Ltd | Real estate | 2026 |
| One TOO One Travel Limited | Transport & logistics | 2025 |
| One View Digital Ltd | Administrative & support | 2020 |
| ONE4FOUR Group Ltd. | Information & communication | 2016 |
| ONE7 Diagnostics Ltd | Health & social care | 2024 |
| Onec Group Limited | Other services | 2022 |
| Onedle Limited | Information & communication | 2018 |
| Onehundred Financial Consulting Ltd | Professional & scientific | 2022 |
| Oneqi Limited | Administrative & support | 2015 |
| Oneqi SPV Limited | Real estate | 2022 |
| Onespirit Interfaith Foundation | Education | 2002 |
| Onestopml Limited | Information & communication | 2021 |
| Onethreesix Homes Limited | Real estate | 2026 |
| Onetwentycatering Ltd | Wholesale & retail | 2022 |
| Onetwoseven Consulting Ltd | Information & communication | 2019 |
| Oneway Electrics Ltd | Construction | 2026 |
| Online Business ABC Ltd | Information & communication | 2023 |
| Online Demonstrations Ltd | Education | 2020 |
| Online Pump Supplies Limited | Administrative & support | 2013 |
| Online Responsibility Network Limited | Information & communication | 2018 |
| Onlineworlduk Ltd | Wholesale & retail | 2020 |
| Only Bathrooms Limited | Wholesale & retail | 2024 |
| Onlyascii Ltd | Information & communication | 2019 |
| Onlyfinance Recruitment Ltd | Administrative & support | 2026 |
| Onmed Limited | Administrative & support | 2012 |
| Onsite Finishing Solutions Ltd | Construction | 2023 |
| Onslow Consulting Limited | Administrative & support | 2022 |
| Ontoscale Limited | Information & communication | 2023 |
| Onyx Fitted Furniture Limited | Extraterritorial | 2025 |
| Onyx Self Drive Hire Ltd | Administrative & support | 2024 |
| Onyxwear Ltd | Manufacturing | 2026 |
| OO Electrical Consultants Limited | Professional & scientific | 2025 |
| OOH Cooling Limited | Other services | 2020 |
| Ooit Limited | Administrative & support | 2024 |
| Oolio Group UK Limited | Information & communication | 2002 |
| Opal Building Projects Limited | Construction | 2026 |
| Opal Consulting Limited | Professional & scientific | 1997 |
| Opal Projects Northwest Ltd | Construction | 2018 |
| Opal Properties Limited | Real estate | 2025 |