| Orbit Money Ltd | Information & communication | 2025 |
| Orbit Travel Partners Ltd | Hospitality | 2025 |
| Orchard Decor Ltd | Extraterritorial | 2014 |
| Orchid & IVY Events Ltd | Hospitality | 2025 |
| Orchid Bookings Limited | Administrative & support | 2025 |
| Orchid Essentials Ltd | Wholesale & retail | 2026 |
| Orcoo Ltd | Extraterritorial | 2025 |
| Orebell Ltd | Extraterritorial | 2026 |
| Orecoll Ltd | Extraterritorial | 2026 |
| Organically Majestic Ltd | Construction | 2021 |
| Oricolor Cosmetics Limited | Manufacturing | 2026 |
| Orient Industry Group Co., Ltd | Extraterritorial | 2013 |
| Orient Mining Limited | Professional & scientific | 2011 |
| Oriental Leaves Limited | Manufacturing | 2025 |
| Origin Arts Communications Limited | Wholesale & retail | 2025 |
| Original Athletics Football Club Ltd | Arts & recreation | 2026 |
| Original Freedom Ltd | Administrative & support | 2025 |
| Origins and Echoes Ltd | Wholesale & retail | 2026 |
| Orinovae Ltd | Wholesale & retail | 2026 |
| Orion Constellation Enterprises Ltd | Information & communication | 2026 |
| Orion Network Limited | Information & communication | 2016 |
| Orion Peak Advisory Limited | Information & communication | 2026 |
| Orion Plumbing and Heating (NW) Ltd | Construction | 2026 |
| Oriplay Ltd | Wholesale & retail | 2025 |
| Orivent Ltd | Wholesale & retail | 2026 |
| Orixpan Limited | Wholesale & retail | 2025 |
| Orlando Tech Limited | Extraterritorial | 2010 |
| Ornithorynque Limited | Administrative & support | 2025 |
| Orsu-Obodo Indigenes in Diaspora CIC | Other services | 2025 |
| Orventra Ltd | Wholesale & retail | 2026 |
| Orvian Capital Limited | Real estate | 2026 |
| Oryntal Ltd | Wholesale & retail | 2025 |
| Orynthbridge UK Ltd | Information & communication | 2026 |
| Osaris Property Limited | Real estate | 2022 |
| OSB House Limited | Wholesale & retail | 2003 |
| Osinigwe Lounge Ltd | Hospitality | 2026 |
| Osono Group Limited | Information & communication | 2018 |
| Ospringe Holdings Ltd | Financial services | 2020 |
| Otakumate Ltd | Information & communication | 2025 |
| Otbfmb Ltd | Extraterritorial | 2025 |
| Ottermire Conservation Ltd | Wholesale & retail | 2025 |
| Otto Properties Limited | Real estate | 2024 |
| Otto Toy Ltd | Wholesale & retail | 2025 |
| Otuh Trfts Trading Limited | Wholesale & retail | 2025 |
| OU Yang Zeng Ltd | Wholesale & retail | 2025 |
| OU Yuan International Trade Co. Ltd | Administrative & support | 2021 |
| Ouddhan Trade Ltd | Wholesale & retail | 2025 |
| Ouliya Industry Co., Ltd | Administrative & support | 2014 |
| Oupstion Ltd | Wholesale & retail | 2025 |
| OUR Digital Horizon Ltd | Information & communication | 2025 |
| OUR World-Underwater Scholarship Society (Europe) Limited | Education | 2001 |
| Ouradmin Limited | Administrative & support | 2021 |
| Ousmetics Ltd | Wholesale & retail | 2025 |
| Outbound Intelligence Group Ltd | Information & communication | 2025 |
| Outlet 64 Limited | Wholesale & retail | 2024 |
| Outsourciax Ltd | Professional & scientific | 2025 |
| Outsourcing (KE) Limited | Information & communication | 2022 |
| Ouxunda Industrial Co., Ltd | Administrative & support | 2021 |
| Ouya Clothing Co., Ltd | Wholesale & retail | 2021 |
| Oval Joya Ltd | Real estate | 2025 |
| Oveify Global Jewels Limited | Manufacturing | 2025 |
| Ovelyn LLP | | 2025 |
| Oven and Spices Limited | Hospitality | 2025 |
| Overlandtrek Ltd | Wholesale & retail | 2025 |
| Overseas People Consulting Ltd | Administrative & support | 2018 |
| Overwatch Technologies Ltd | Information & communication | 2025 |
| Ovivra Ltd | Wholesale & retail | 2025 |
| Ovyno Limited | Wholesale & retail | 2025 |
| OWE Solutions Ltd | Construction | 2025 |
| Owen & Brown Ltd | Information & communication | 2025 |
| Owen & Brown Services Limited | Administrative & support | 2025 |
| Own Your Aura Limited | Wholesale & retail | 2026 |
| Owtv Ltd | Information & communication | 2026 |
| OX and Bucks Construction Consultancy Services Limited | Construction | 2015 |
| Oxford Academic Nexus CIC | Professional & scientific | 2025 |
| Oxford CNS Limited | Health & social care | 2022 |
| Oxford International Medical Technology Research and Development Co., Ltd | Professional & scientific | 2019 |
| Oxford Origin Limited | Manufacturing | 2022 |
| Oxford School for Applied Studies - Osas Ltd | Education | 2023 |
| Oxford Theatricals Ltd | Arts & recreation | 2024 |
| Oxford-Arch Medical Services Ltd | Administrative & support | 2026 |
| Oxfordshire Melts & Candles Ltd | Manufacturing | 2022 |
| Oxka Private Limited | Wholesale & retail | 2021 |
| Oxvor UK Ltd | Wholesale & retail | 2019 |
| OXY Information Technology Ltd | Information & communication | 2022 |
| Oyetoki Enterprises Ltd | Wholesale & retail | 2026 |
| OYO Land Management (Andover) Limited | Real estate | 2004 |
| Oysters and Pebbles Auto Ltd | Wholesale & retail | 2025 |
| Oyuyk Chia Trading Limited | Wholesale & retail | 2025 |
| Ozeri Ltd | Wholesale & retail | 2025 |
| Ozman Limited | Real estate | 2025 |
| P & E Products Ltd | Wholesale & retail | 2024 |
| P and P INT Trading Ltd | Wholesale & retail | 2019 |
| P Parker Operator Services Limited | Construction | 2018 |
| P. R. S. (LON) Limited | Professional & scientific | 2008 |
| P.R.A Gallery Ltd | Wholesale & retail | 2025 |
| P2M Solutions Ltd | Professional & scientific | 2023 |
| PAB Property & Garden Services Ltd | Construction | 2021 |
| Pacam Properties Ltd | Real estate | 2019 |
| Paceonis Slauson Ltd | Wholesale & retail | 2025 |