| Office Vitals Ltd | Wholesale & retail | 2018 |
| Official Amzon Ltd | Wholesale & retail | 2025 |
| Official Musk Ltd | Wholesale & retail | 2025 |
| Official NUA Limited | Wholesale & retail | 2022 |
| Offmarket Ltd | Wholesale & retail | 2024 |
| Offsite I T Limited | Information & communication | 2006 |
| Oflox Ltd | Wholesale & retail | 2019 |
| OG Car Kits Ltd | Wholesale & retail | 2025 |
| OG Car World Limited | Wholesale & retail | 2024 |
| Ogct Ltd | Hospitality | 2024 |
| Ogecares Limited | Health & social care | 2020 |
| Ogeo FIX Ltd | Construction | 2018 |
| Ogeremit Limited | Financial services | 2022 |
| OH My Optics Limited | Wholesale & retail | 2025 |
| Ohene Homes Ltd | Real estate | 2024 |
| Ohent Capital Limited | Financial services | 2022 |
| Ohlips Ltd | Information & communication | 2025 |
| OHM Electrical Engineering Ltd | Manufacturing | 2018 |
| Oigamenollc Limited | Wholesale & retail | 2025 |
| Oiltech OIL and GAS Services UK Ltd | Manufacturing | 2021 |
| Oituz Logistics Ltd | Transport & logistics | 2018 |
| OJ Kennedy Construction Ltd | Construction | 2021 |
| OJ Structures Ltd | Construction | 2025 |
| Ojay Halls Ltd | Professional & scientific | 2026 |
| Ojeen London Ltd | Hospitality | 2025 |
| Ojeeninternational Ltd | Hospitality | 2025 |
| Ojha Ltd | Professional & scientific | 2026 |
| OK Brothers Ltd | Wholesale & retail | 2013 |
| OK Hawram Builders Ltd | Construction | 2025 |
| Okey Intercon Limited | Information & communication | 1997 |
| OKO Lounge Ltd | Arts & recreation | 2017 |
| OKO Resto Lounge Ltd | Hospitality | 2026 |
| OL Logistics Ltd | Transport & logistics | 2026 |
| OLA Structures Limited | Other services | 2026 |
| Olaiya Accessories Ltd | Wholesale & retail | 2019 |
| Olasfem Ltd | Construction | 2020 |
| Olcs Ltd | Wholesale & retail | 2015 |
| Old Martin Ltd | Manufacturing | 2019 |
| Old Mill Market Ltd | Wholesale & retail | 2026 |
| Oldford Services Ltd | Health & social care | 2022 |
| OLE Consultants Ltd | Construction | 2022 |
| Olearned Ltd | Professional & scientific | 2025 |
| Oleoland Hotel Company Limited | Real estate | 1990 |
| Oligoflow Limited | Wholesale & retail | 2026 |
| Olisstar Limited | Construction | 2021 |
| Olive Branch Trading Ltd | Wholesale & retail | 2020 |
| Olive Breeze UK Consulting Limited | Wholesale & retail | 2007 |
| Olive Gardens Entertainment Ltd | Hospitality | 2017 |
| Olive Light Consulting (OLC) Limited | Information & communication | 2011 |
| Olive SI Limited | Other services | 2021 |
| Oliver One Ltd | Construction | 2014 |
| Oliver Stern Services Limited | Administrative & support | 2019 |
| Olives Eight Ltd | Wholesale & retail | 2012 |
| Olivia Rocco Limited | Wholesale & retail | 2025 |
| Olivia Rose UK Limited | Information & communication | 2001 |
| Olivio Cristina Ltd | Transport & logistics | 2025 |
| Olli Productions Ltd | Information & communication | 2024 |
| Ollieossay Ltd | Wholesale & retail | 2015 |
| Ollos Technology Ltd | Information & communication | 2023 |
| OLY Properties Limited | Real estate | 2025 |
| Olympia Roofing Ltd | Construction | 2025 |
| Olympus Homes Inc Limited | Construction | 2024 |
| OM Care Properties Limited | Real estate | 2023 |
| OM IT Consulting Limited | Information & communication | 2010 |
| OM Logistics Distribution Ltd | Transport & logistics | 2025 |
| OM Property Essex Ltd | Real estate | 2020 |
| OM Shringar Ltd | Wholesale & retail | 2026 |
| OM SRI Housing Ltd | Real estate | 2025 |
| Omar Transport Ltd | Transport & logistics | 2026 |
| Omazuike Ltd | Health & social care | 2021 |
| OMC General UK Ltd | Wholesale & retail | 2022 |
| Omega Crew Ltd | Information & communication | 2024 |
| OMEGA3 Consulting Ltd | Information & communication | 2020 |
| Omenma NDI IMO Ltd | Professional & scientific | 2020 |
| Omenma Ndimo Foundation | Other services | 2020 |
| Omer Optometric Services Ltd | Health & social care | 2018 |
| Omerix Security Ltd | Administrative & support | 2025 |
| Omex Fashions Limited | Real estate | 1990 |
| Ominira Writers CIC | Education | 2024 |
| Omiris Consult Ltd | Financial services | 2010 |
| Omis Global Limited | Wholesale & retail | 2025 |
| Ommer Group Limited | Real estate | 2021 |
| Ommynom Ltd | Manufacturing | 2022 |
| Omnia Collection Limited | Education | 2023 |
| Omnideals Ltd | Wholesale & retail | 2025 |
| Omnimed Healthcare Limited | Wholesale & retail | 2020 |
| Omnivex International Ltd | Wholesale & retail | 2025 |
| Omnivision Solutions Ltd | Information & communication | 2023 |
| OMO Consultancy Services Ltd | Health & social care | 2021 |
| Omon RA Ltd | Construction | 2023 |
| OMS Properties (London) Ltd | Real estate | 2021 |
| Omshiv Enterprises Ltd | Real estate | 2025 |
| OMT Car and Commercial Ltd | Professional & scientific | 2022 |
| Omvex Limited | Information & communication | 2026 |
| ON Air Media Group Limited | Professional & scientific | 2016 |
| ON Point Study Limited | Education | 2022 |
| ON Site Safe Ltd | Construction | 2025 |
| ON the Bench Podcast Ltd | Information & communication | 2023 |
| ON the Money Productions Limited | Information & communication | 2021 |
| ON Time Suppliers Ltd | Professional & scientific | 2025 |