| Olde Toll House Ltd | Hospitality | 2025 |
| Oldsters Elite Home Care Ltd | Health & social care | 2022 |
| OLE QIM Ltd | Wholesale & retail | 2025 |
| Olea Properties Ltd | Real estate | 2022 |
| Olegijus Ltd | Other services | 2025 |
| Olenix Web Solutions Ltd | Information & communication | 2023 |
| Oleti Consulting Ltd | Information & communication | 2025 |
| Oliart Ltd | Construction | 2020 |
| Olir Properties Maintenance and Services Ltd | Real estate | 2023 |
| Olive Lights Healthcare Ltd | Health & social care | 2025 |
| Olive Properties & Investments Ltd | Real estate | 2017 |
| Oliver Chapman Ltd | Construction | 2021 |
| Oliver Charles Antiques Limited | Wholesale & retail | 2001 |
| Ollie B Services Ltd | Construction | 2025 |
| Olmeet Limited | Real estate | 2021 |
| Olmexa Limited | Wholesale & retail | 2025 |
| Olympus PM Construction Ltd | Construction | 2026 |
| OM Courier Limited | Transport & logistics | 2026 |
| OM Saravanabhava Ltd | Real estate | 2020 |
| OM Teknology Limited | Wholesale & retail | 2026 |
| Omaks Energy Ltd | Information & communication | 2012 |
| Omarlittlesbarbers Ltd | Other services | 2025 |
| Omarzada Limited | Other services | 2025 |
| OME Plumbing & Heating Ltd | Construction | 2020 |
| Omega Experts Ltd | Administrative & support | 2025 |
| OMG DXB Ltd | Professional & scientific | 2026 |
| Omid's Tennis Academy Ltd | Education | 2025 |
| OMK Dryliner Ltd | Construction | 2023 |
| Omni Trading Hub Ltd | Wholesale & retail | 2020 |
| Omni Web Creators Ltd | Information & communication | 2024 |
| Omnia Resourcing Ltd | Administrative & support | 2021 |
| Omnicam Cctv Services Limited | Construction | 2025 |
| Omnicorp Management Limited | Real estate | 2014 |
| ON Point Business Associates Limited | Professional & scientific | 2025 |
| ON Stores Ltd | Wholesale & retail | 2026 |
| ON4T Ltd | Wholesale & retail | 2025 |
| One 8 Extra Limited | Wholesale & retail | 2024 |
| One Fitness Limited | Arts & recreation | 2014 |
| One Foods Ltd | Hospitality | 2023 |
| One in ALL Outlet Ltd | Wholesale & retail | 2023 |
| One Management Group Ltd | Professional & scientific | 2019 |
| One Professional Cleaning Service Ltd | Administrative & support | 2025 |
| One Stop Distribution Ltd | Wholesale & retail | 2025 |
| One Stop Food Store Limited | Wholesale & retail | 2011 |
| One Stop Groceries Limited | Wholesale & retail | 2023 |
| One Stop Solution Accountants Limited | Administrative & support | 2021 |
| One to One MDS Consulting Ltd | Professional & scientific | 2011 |
| One World Group Holdings Ltd | Real estate | 2017 |
| Oneformation UK Limited | Wholesale & retail | 2021 |
| Oneida Life Ltd | Construction | 2023 |
| Onemarsmedia Limited | Professional & scientific | 2024 |
| Onetwo Innovations Limited | Information & communication | 2025 |
| Onguard Services Ltd | Administrative & support | 2021 |
| Onkar Building Works Ltd | Construction | 2025 |
| Online Educators Ltd | Education | 2015 |
| Onlineselluk Limited | Wholesale & retail | 2025 |
| Only Organic Wellness Ltd | Wholesale & retail | 2024 |
| Onyx Guardian Ltd | Wholesale & retail | 2025 |
| OOM Software Ltd | Information & communication | 2015 |
| Ooohmy Style Ltd | Manufacturing | 2023 |
| Opal Design & Construct Ltd | Real estate | 2026 |
| Open Door Pictures Ltd | Information & communication | 2025 |
| Open Way to Late Limited | Wholesale & retail | 2026 |
| Openhouse Twickenham Ltd | Real estate | 2024 |
| Oppona Limited | Real estate | 2021 |
| Opportunity Properties Ltd | Construction | 2016 |
| Oprea Group Limited | Financial services | 2025 |
| Optimum Asset Investments Limited | Real estate | 2022 |
| Optimum Recycling Services Ltd | Water & waste | 2025 |
| Optireview Ltd | Information & communication | 2026 |
| Optivus Consultants Ltd | Information & communication | 2024 |
| Opturion Limited | Professional & scientific | 2021 |
| Orain Limited | Wholesale & retail | 2026 |
| Orange Security Ltd | Administrative & support | 2023 |
| Orange Transgroup Ltd | Transport & logistics | 2012 |
| Oranium Limited | Wholesale & retail | 2014 |
| Oras Business Services Limited | Professional & scientific | 2012 |
| ORB Wellbeing Ltd | Information & communication | 2021 |
| Orbi Ltd | Information & communication | 2025 |
| Orbis Edifice Limited | Real estate | 2025 |
| Orbital Trading Limited | Transport & logistics | 2015 |
| Orchard Ridge Ltd | Extraterritorial | 2022 |
| Oredd Limited | Wholesale & retail | 2025 |
| Orel Brothers Ltd | Construction | 2024 |
| Organic Maya Ltd | Wholesale & retail | 2026 |
| Organic Nuts and Spices Limited | Wholesale & retail | 2025 |
| Oriental Sun Ltd | Hospitality | 2023 |
| Original Karahi Ltd | Hospitality | 2024 |
| Origzon Limited | Financial services | 2022 |
| Orin Limited | Construction | 2022 |
| Orlik Z Ltd | Wholesale & retail | 2018 |
| Orthoprosmile Ltd | Health & social care | 2018 |
| Orzey Trading Limited | Wholesale & retail | 2025 |
| Osborne Logistics Ltd | Transport & logistics | 2025 |
| Oscar Essentials Ltd | Wholesale & retail | 2016 |
| Oscorp Industries Ltd | Health & social care | 2023 |
| Osman Plumbing & Heating Services Ltd | Construction | 2014 |
| Osterley Developements Limited | Real estate | 2019 |
| Osterley Meat Market Ltd. | Wholesale & retail | 2024 |
| Osterley Outings Limited | Other services | 2024 |