| OM Construction Services Limited | Construction | 2014 |
| OM Medical Services Limited | Administrative & support | 2016 |
| Omcas Limited | Professional & scientific | 2026 |
| Omega Bricks Properties Ltd | Real estate | 2025 |
| Omega Creation Limited | Administrative & support | 2017 |
| Omega Express Couriers Ltd | Transport & logistics | 2010 |
| Omega Suites Ltd | Real estate | 2023 |
| Omega Systems & Services Ltd | Wholesale & retail | 2022 |
| Omega-Wellness Ltd | Wholesale & retail | 2019 |
| Omex Property Services Limited | Real estate | 2003 |
| Omika Homes Ltd | Real estate | 2024 |
| OML2025 Limited | Real estate | 2020 |
| Omnes Bay Ltd | Wholesale & retail | 2020 |
| Omni Cycle Ltd | Wholesale & retail | 2020 |
| Omni Traders Limited | Wholesale & retail | 2025 |
| Omnicraft Ltd | Construction | 2024 |
| Omnihouse Supplies Ltd | Wholesale & retail | 2025 |
| Omniscient Marketing UK Limited | Professional & scientific | 2023 |
| Omnitech Services Limited | Information & communication | 2016 |
| Omniversity of Knowledge Ltd | Education | 2023 |
| OMO Mase Limited | Hospitality | 2014 |
| Omok&S Ltd | Real estate | 2023 |
| OMR Trading Limited | Construction | 2025 |
| ON Call Engineers Ltd. | Construction | 2024 |
| ON Line Registrars Limited | Professional & scientific | 1996 |
| ON the Bubble Drylining Limited | Construction | 2019 |
| ON the Money Store Limited | Wholesale & retail | 2023 |
| ON2SITE Limited | Administrative & support | 2025 |
| Oncilla Limited | Financial services | 2012 |
| Ondris Ltd | Wholesale & retail | 2025 |
| One and Only Group Limited | Wholesale & retail | 2019 |
| One Brick Ltd | Real estate | 2021 |
| One Call Away Ltd | Administrative & support | 2026 |
| One Call GAS Works Ltd | Administrative & support | 2017 |
| One Day, Day One Coaching Ltd | Health & social care | 2024 |
| One From the Best Limited | Transport & logistics | 2025 |
| One Gaming Limited | Real estate | 2022 |
| One Kart Ltd | Wholesale & retail | 2020 |
| One Name Antony Limited | Wholesale & retail | 2018 |
| One One Two Menswear Limited | Wholesale & retail | 2020 |
| One Project Limited | Construction | 2026 |
| One Sky Ventures Enterprise Ltd | Administrative & support | 2022 |
| One Stop Audit Limited | Professional & scientific | 2009 |
| One Stop Auto Spare Parts Limited | Wholesale & retail | 2025 |
| One Stop Education Ltd | Education | 2014 |
| One to One Films Services Ltd | Arts & recreation | 2020 |
| One to One Pack Limited | Administrative & support | 2025 |
| One Two One Counseling Services Limited | Professional & scientific | 2013 |
| ONE10 Construction Ltd | Construction | 2021 |
| ONE64DIECAST Limited | Wholesale & retail | 2020 |
| Onenest Services Ltd | Professional & scientific | 2025 |
| Onesqure Limited | Real estate | 2025 |
| Onetake Visuals Ltd | Information & communication | 2021 |
| Onetrisoft Ltd | Information & communication | 2021 |
| Onetrue Limited | Administrative & support | 1974 |
| Onewealth Ltd | Administrative & support | 2020 |
| Onexa Capital Ltd | Real estate | 2025 |
| Onexa Ltd | Administrative & support | 2025 |
| Onicrest Transport Ltd | Transport & logistics | 2020 |
| Onitlikeacarbonnet Ltd | Wholesale & retail | 2019 |
| Online Business 4 YOU Limited | Hospitality | 2017 |
| Online MOT Ltd | Wholesale & retail | 2020 |
| Online Shoppe Zamb Ltd | Wholesale & retail | 2025 |
| Online Watch Accessories Limited | Wholesale & retail | 2022 |
| ONLINE2HEAVEN Ltd | Wholesale & retail | 2023 |
| Onlineamz Ltd | Wholesale & retail | 2023 |
| ONLINESALES247UK Ltd | Wholesale & retail | 2025 |
| Only Good Times Ahead Limited | Hospitality | 2026 |
| Onryy Ltd | Wholesale & retail | 2026 |
| Onspire Media Limited | Wholesale & retail | 2024 |
| Ontime Delivery Ltd | Transport & logistics | 2020 |
| Onyxinc Ltd | Wholesale & retail | 2023 |
| Onyy Ltd | Wholesale & retail | 2026 |
| Onzoo Ltd | Manufacturing | 2026 |
| Oomla Ltd | Professional & scientific | 2022 |
| Oops Kazmi Limited | Real estate | 2020 |
| OP Aerosols Limited | Wholesale & retail | 2023 |
| OP Online Limited | Manufacturing | 2025 |
| Opal Pro Cleaning Ltd | Administrative & support | 2026 |
| Opal Sapphire Properties Ltd | Real estate | 2022 |
| Opalvale Limited | | 1973 |
| OPC Carpentry Ltd | Manufacturing | 2025 |
| Open B Gateway Limited | Information & communication | 2019 |
| Opes Finance Consulting Ltd | Information & communication | 2018 |
| Ophc Diamond Trading Limited | Wholesale & retail | 2025 |
| Ophthalunit Limited | Health & social care | 2025 |
| Oppal Smiles Limited | Health & social care | 2026 |
| Oprean Trans Ltd | Transport & logistics | 2020 |
| Opris C Trans Ltd | Transport & logistics | 2022 |
| Opsbo Digital Limited | Other services | 2023 |
| Opscel Ltd | Information & communication | 2026 |
| Opti Chef Limited | Extraterritorial | 2015 |
| Opti Property Limited | Hospitality | 2017 |
| Opti-Lighting Limited | Manufacturing | 2014 |
| Optic NET Construction Ltd | Construction | 2025 |
| Opticon Limited | Wholesale & retail | 1990 |
| Optielite Innovations Limited | Manufacturing | 2024 |
| Optiflow Mechanical Ltd | Construction | 2025 |
| Optik Eyecare Limited | Wholesale & retail | 2023 |
| Optima Property Funding Limited | Financial services | 2008 |