| Old Drayton Limited | Hospitality | 2014 |
| Old Hayes Property Ltd | Real estate | 2023 |
| Old Lion Limited | Financial services | 2025 |
| Old Mill Homes Ltd | Construction | 2021 |
| Old Newtonians Rugby Football Club Limited | Arts & recreation | 2012 |
| Old OWL Inns (Black Horse) Limited | Hospitality | 2018 |
| Old School Brand UK Ltd | Manufacturing | 2025 |
| Old Station Close (Whetstone) Management Limited | Households | 2014 |
| Old Station Road Holdings Limited | Professional & scientific | 1996 |
| Old Vicarage Holdings Ltd | Financial services | 2025 |
| Old Wood Court (Burton on the Wolds) Limited | Households | 2020 |
| Olevisio Ltd | Professional & scientific | 2025 |
| Olgc Satellite Club Limited | Arts & recreation | 2020 |
| Olivaro Ltd | Hospitality | 2026 |
| Olive Electrical Services Limited | Construction | 2025 |
| Olive Homes and Property Ltd | Real estate | 2026 |
| Olive Leaf Estates Ltd | Real estate | 2020 |
| Olive Leaf Lettings Ltd | Real estate | 2023 |
| Olive Tree Dental Practice Limited | Health & social care | 2006 |
| Olive Tree Holdings and Investment Limited | Real estate | 2019 |
| Olive Trees Express Limited | Hospitality | 2017 |
| Olive Trees Restaurant Limited | Hospitality | 2017 |
| Oliver Barber Limited | Other services | 2024 |
| Oliver Court Development Ltd | Real estate | 2013 |
| Oliver Rayns Limited | Real estate | 2017 |
| Oliver's Crazy Cuts Ltd | Other services | 2025 |
| Oliver's Entertainment Limited | Hospitality | 2012 |
| Oliver's Properties Limited | Real estate | 2015 |
| Oliveti Accessibility Limited | Professional & scientific | 2010 |
| Oliveti Construction Limited | Construction | 2001 |
| Oliveti Group Ltd | Professional & scientific | 2014 |
| Oliveti Manufacturing Limited | Administrative & support | 2014 |
| Olivia House Management Partnership Ltd | Households | 2022 |
| Olivia India Limited | Wholesale & retail | 2009 |
| Olivia James Leicester Ltd | Financial services | 2025 |
| Olivia LUX Ltd | Manufacturing | 2022 |
| Olivia Teare & Co Ltd | Wholesale & retail | 2025 |
| Olivia Thomas Limited | Education | 2015 |
| Olivia's Properties Ltd | Real estate | 2020 |
| OLIVIA2017 Limited | Transport & logistics | 2016 |
| Olla Post Birth Support Ltd | Education | 2024 |
| Ollie Ollie Ltd | Information & communication | 2018 |
| Ollurs Limited | Wholesale & retail | 2024 |
| OLM Marketing Ltd | Professional & scientific | 2025 |
| Olney Business Park MC Limited | Real estate | 2007 |
| Olotrans Ltd | Transport & logistics | 2022 |
| Oloughlin Smiles Ltd | Health & social care | 2024 |
| Oloye Aesthetics Ltd | Other services | 2021 |
| Olwen M Davies Limited | Professional & scientific | 2002 |
| Olympiaa Ltd | Hospitality | 2021 |
| Olympus Eyewear UK Limited | Wholesale & retail | 2019 |
| OM (Leicester) Limited | Real estate | 2006 |
| OM Construction Limited | Construction | 2019 |
| OM Courier Worldwide Parcel Service Limited | Transport & logistics | 2025 |
| OM Cutting Leicester Ltd | Manufacturing | 2018 |
| OM Dhriti Enterprise Ltd | Water & waste | 2023 |
| OM Express Limited | Transport & logistics | 2023 |
| OM Funeral Services Limited | Other services | 2013 |
| OM Installations Ltd | Construction | 2024 |
| OM Namah Shivaya Limited | Health & social care | 2023 |
| OM News Limited | Other services | 2016 |
| OM Properties Investment Company Limited | Real estate | 1985 |
| OM Properties Leicester Ltd | Real estate | 2026 |
| OM Property Invesment Ltd | Real estate | 2023 |
| OM SAI Trading Ltd | Hospitality | 2019 |
| OM Shanti OM Ltd | Other services | 2025 |
| OM Shri Ganesh Ltd | Real estate | 2025 |
| Omac Group Ltd | Administrative & support | 2024 |
| Oman Global Capital Limited | Extraterritorial | 2017 |
| Omanex International Ltd | Financial services | 2025 |
| Omar Estates (Leic) Ltd | Real estate | 2022 |
| Omar Investments Ltd | Households | 2025 |
| Omarji Investments Limited | Real estate | 2013 |
| OMC Youth Enterprise Limited | Health & social care | 2022 |
| Omega 89 Store Ltd | Wholesale & retail | 2023 |
| Omega Consultants Ltd | Professional & scientific | 2024 |
| Omega Engineering Services Ltd | Manufacturing | 2018 |
| Omega Garments Ltd | Manufacturing | 2018 |
| Omenya Ltd | Information & communication | 2019 |
| Omer's Cleaning Service Ltd | Administrative & support | 2026 |
| OMI Bar Ltd | Hospitality | 2020 |
| Omni Consultant Ltd | Information & communication | 2014 |
| Omni Resources Ltd | Administrative & support | 2025 |
| Omni Telecom Ltd | Information & communication | 2023 |
| Omni Trove Properties Ltd | Real estate | 2025 |
| Omniche Ltd | Information & communication | 2025 |
| Omnidea Ltd | Professional & scientific | 2018 |
| Omniguard Consulting Ltd | Information & communication | 2024 |
| Omniphi Systems Limited | Information & communication | 2006 |
| Omom Ltd | Information & communication | 2025 |
| Omsai Equity CAP Ltd | Real estate | 2026 |
| Omumbeejumbee Records Ltd | Arts & recreation | 2025 |
| OMV Build Solution Limited | Construction | 2019 |
| OMW Holdings Limited | Administrative & support | 2026 |
| ON Fire Stoves Ltd | Wholesale & retail | 2023 |
| ON Firs Management Ltd | Households | 2016 |
| ON Grow Ltd | Transport & logistics | 2023 |
| ON International Media Ltd | Administrative & support | 2022 |
| ON IT 1ST Ltd | Wholesale & retail | 2025 |
| ON Poynt Creative Ltd | Professional & scientific | 2022 |