| Oaklawn (Horsell) Management Company Limited | Households | 1997 |
| Oakley Property Lettings Ltd | Real estate | 2020 |
| Oakley Property Solutions Limited | Real estate | 2006 |
| Oakley Support Services Ltd | Administrative & support | 2011 |
| Oakwrights Limited | Construction | 1995 |
| Oasis Building Services Limited | Construction | 2024 |
| Oasis Electrics Limited | Construction | 2012 |
| Oasis Property Lettings Limited | Real estate | 2022 |
| Occam Arts Limited | Information & communication | 2026 |
| Ocean Grown Ornamentals Limited | Agriculture & fishing | 2023 |
| Oceania UK Limited | Wholesale & retail | 2004 |
| Oceanpoint Maintenance Ltd | Households | 2017 |
| Oceanview Group Limited | Financial services | 2023 |
| Ocelli Capital Partners Ltd | Other services | 2022 |
| Ocon Solutions Ltd | Professional & scientific | 2022 |
| Octarine Systems Ltd | Information & communication | 2026 |
| Octavio Management Ltd | Households | 2013 |
| Oddly Clean Exteriors Ltd | Administrative & support | 2026 |
| OFF Beat Therapy CIC | Health & social care | 2026 |
| OFF the Cage Ltd | Wholesale & retail | 2025 |
| OFF the Wall Padel Ltd | Arts & recreation | 2024 |
| Officers Park (Management) Limited | Households | 2025 |
| Ofpm Ltd | Real estate | 2025 |
| OH My WAX Limited | Other services | 2025 |
| Ojkos Ltd | Transport & logistics | 2025 |
| OJR Services Ltd | Agriculture & fishing | 2024 |
| OK Go Studio Ltd | Professional & scientific | 2023 |
| Old Julius Yard (Wrecclesham) Residents Association Limited | Households | 2020 |
| Old Knowle Square Management Limited | Households | 2023 |
| Old Wicks Limited | Real estate | 2006 |
| Oldaker Investments Limited | Financial services | 2025 |
| Oliso Investments | Financial services | 2025 |
| Olive Grove Group Limited | Hospitality | 2025 |
| Olivet Homes Limited | Hospitality | 2023 |
| Olivia White Design Ltd | Professional & scientific | 2012 |
| Olli Caldwell Promotions Ltd | Administrative & support | 2017 |
| Ollil Ltd | Hospitality | 2025 |
| Omdb Limited | Construction | 2023 |
| Ominous Ltd | Wholesale & retail | 2023 |
| OMP Stud Limited | Agriculture & fishing | 2011 |
| On-Point Accountancy Ltd | Administrative & support | 2016 |
| One Short Media Limited | Other services | 2014 |
| Oneonefour Restaurant Limited | Hospitality | 2016 |
| Oneoseven Media Solutions Ltd | Information & communication | 2022 |
| Online Azure Consulting Limited | Information & communication | 2022 |
| Online Therapy Ltd | Extraterritorial | 2012 |
| Onlinem Ltd. | Information & communication | 2011 |
| Only Blue Limited | Professional & scientific | 2020 |
| ONS Management Limited | Real estate | 2018 |
| ONSET999 Limited | Extraterritorial | 2022 |
| Onsite Heating Limited | Construction | 2024 |
| Onslow Mews Management Limited | Households | 2011 |
| Onyx Groundworks & Landscaping Ltd | Construction | 2019 |
| Onyx Group Surrey Ltd | Construction | 2022 |
| Open Minds Development Ltd | Education | 2024 |
| Open Synergy Limited | Information & communication | 2022 |
| Openshaw & Co. Employee Trustee Limited | Extraterritorial | 2021 |
| Opes Strategy Group Ltd | Administrative & support | 2020 |
| Ophtha Ventures Ltd | Professional & scientific | 2021 |
| Oplex Digital Ltd | Information & communication | 2024 |
| Opticheck Ltd | Information & communication | 2024 |
| Optise Ltd | Professional & scientific | 2026 |
| Optoconsult Ltd | Professional & scientific | 2021 |
| Opus Pharmacy Services Limited | Education | 2004 |
| Orange Bay Limited | Financial services | 2024 |
| Orange Electrical & Renewables Limited | Construction | 2025 |
| Orange Taxis Ltd | Administrative & support | 2016 |
| ORB Surrey Limited | Professional & scientific | 2021 |
| Orbit Housing Ltd | Real estate | 2023 |
| Orchard Court (Weyhill) Management Limited | Households | 1999 |
| Orchard House Management Limited | Households | 1978 |
| Orchard Team Solutions Limited | Professional & scientific | 2012 |
| Orchestrato Ltd | Professional & scientific | 2013 |
| Orchid Development Limited | Construction | 2018 |
| Orchid Digital Ltd | Professional & scientific | 2012 |
| Oregano Solutions Limited | Administrative & support | 2025 |
| Oriana Consultants Limited | Professional & scientific | 1997 |
| Origin Books & Media Limited | Wholesale & retail | 1991 |
| Origins Healthcare Communications Limited | Administrative & support | 2018 |
| Orion Cinemas Limited | Hospitality | 1995 |
| Orion Image Limited | Information & communication | 2009 |
| Orlie Limited | Construction | 2025 |
| Orphan Insight Ltd | Professional & scientific | 2014 |
| Orta Asia Baspasy Limited | Professional & scientific | 2020 |
| Osgooddepot Ltd | Wholesale & retail | 2024 |
| Osiiris Stunts Ltd | Construction | 2010 |
| Osiris Developments Ltd | Real estate | 2013 |
| Osmo Limited | Professional & scientific | 1989 |
| OSP Architecture Limited | Financial services | 2025 |
| Ostrom-Hall Software Limited | Professional & scientific | 2024 |
| Ostrotek Ltd | Information & communication | 2023 |
| Otion Investments Limited | Administrative & support | 2014 |
| Otus Live in Care Ltd | Health & social care | 2011 |
| Outbrand Ltd | Professional & scientific | 2019 |
| Outdoor Living Inspiration Ltd | Wholesale & retail | 2020 |
| Outstanding Cufflink Designs Limited | Manufacturing | 2011 |
| Oval Farncombe Management Company Limited | Households | 2014 |
| Over Ice Ltd | Wholesale & retail | 2012 |
| Overworld AMP Limited | Education | 2022 |
| OWL Mill Properties Limited | Real estate | 2024 |