| Oak Farm Drive Management Company Limited | Administrative & support | 2011 |
| Oak Zone Biotech UK Ltd | Wholesale & retail | 2018 |
| Oakbits Ltd | Information & communication | 2026 |
| Oakbourn Limited | Manufacturing | 2016 |
| Oakdale Property Development Ltd | Real estate | 2020 |
| Oakdene Pharmaceuticals Ltd | Manufacturing | 2024 |
| Oake Investments Ltd | Real estate | 2017 |
| Oakfield Village Estate Management Company Limited | Households | 2016 |
| Oakfields (Camberley) Limited | Households | 1986 |
| Oakfields Residents Management Company Ltd | Households | 2021 |
| Oakham Heights Residents Management Company Limited | Households | 2011 |
| Oakhurst Court Management Company Limited | Households | 2001 |
| Oakington Business Park Management Company Limited | Real estate | 2004 |
| Oakington Design Studio Limited | Professional & scientific | 2021 |
| Oakington Dog Day Care Centre Limited | Other services | 2016 |
| Oakington Garden Centre Limited | Wholesale & retail | 2006 |
| Oakington Property Consultants Limited | Financial services | 2019 |
| Oakland Innovation Ltd | Professional & scientific | 1989 |
| Oakleaf Court (Ascot) Limited | Households | 1994 |
| Oakleigh Event Management Limited | Arts & recreation | 2005 |
| Oakley Court Property Management Limited | Households | 2023 |
| Oakley Street Asset Management | Professional & scientific | 2008 |
| Oakridge Biotech Solutions Ltd | Professional & scientific | 2026 |
| Oaks Services (Cambridge) Ltd. | Professional & scientific | 2015 |
| Oakwell Place Management Limited | Households | 2022 |
| OAS Consultancy Limited | Professional & scientific | 2010 |
| Oasis Asset Associates Limited | Professional & scientific | 2004 |
| Oasis Fabric Workshop Ltd | Wholesale & retail | 2023 |
| Oasismarine Co., Ltd | Extraterritorial | 2022 |
| Oath Healthcare Franchising Ltd | Administrative & support | 2024 |
| Oath Healthcare Limited | Administrative & support | 2020 |
| Oath Training & Consulting Limited | Education | 2025 |
| OB Building Ltd | Construction | 2024 |
| Obai Ltd | Wholesale & retail | 2023 |
| Objective Imaging Limited | Professional & scientific | 2000 |
| Objenix Limited | Information & communication | 1997 |
| Obrizum Group Ltd. | Professional & scientific | 2015 |
| Obscrewity Ltd | Construction | 2025 |
| Obscure Technologies Ltd | Information & communication | 2024 |
| Obstevenson Holdings Limited | Financial services | 2024 |
| Obtuse Goose Ltd | Administrative & support | 2012 |
| Occam Grey Ltd | Professional & scientific | 2019 |
| Occam Research Services LLP | | 2021 |
| Occitania Ltd | Information & communication | 1989 |
| Ocean Embrace Ltd | Wholesale & retail | 2024 |
| Ocean Industry Co., Ltd | Wholesale & retail | 2016 |
| Ocean Mind Property Management Limited | Real estate | 2022 |
| Ocean Success Shipping Company Limited | Extraterritorial | 2014 |
| Ocean Wisdom Education Limited | Education | 2016 |
| Oceana Holiday Homes Ltd | Hospitality | 2024 |
| Oceania West Parade Limited | Extraterritorial | 1998 |
| Oceanic Teakdecking Ltd | Manufacturing | 2024 |
| Oceanmead Limited | Households | 1986 |
| Ocho Rios Ltd | Real estate | 2008 |
| OCR Nationals | Education | 2002 |
| Ocrintelligenceit Ltd | Information & communication | 2025 |
| Ocruh Limited | Professional & scientific | 2019 |
| Octa Design & Build Limited | Construction | 2024 |
| Octa Group Limited | Professional & scientific | 2020 |
| Octa Ride Limited | Arts & recreation | 2025 |
| Octafinity Ltd | Information & communication | 2016 |
| Octava Capital Ltd | Manufacturing | 2026 |
| Octavian Park Management Company Limited | Households | 2002 |
| Octiocor Ltd | Professional & scientific | 2022 |
| October Dawn Limited | Manufacturing | 2014 |
| Octopus Forest | Administrative & support | 2024 |
| Octoshrew Ltd | Information & communication | 2021 |
| Octue Ltd | Professional & scientific | 2013 |
| Ocula Technologies Holdings Limited | Information & communication | 2021 |
| Odackal Limited | Health & social care | 2013 |
| Odbuyit Ltd | Real estate | 2021 |
| Oddo Oddo Ltd | Manufacturing | 2025 |
| Odds & EMS Ltd | Wholesale & retail | 2020 |
| Odes AI Limited | Information & communication | 2024 |
| Odin Intelligence Limited | Administrative & support | 2015 |
| Odreight Commercial Cleaning Solutions Ltd | Administrative & support | 2020 |
| Odreight Domestic Cleaning Solutions Ltd | Administrative & support | 2020 |
| Odusa International Limited | Wholesale & retail | 2025 |
| OE Technology Ltd | Wholesale & retail | 2022 |
| OEM SWS Co., Ltd | Wholesale & retail | 2024 |
| OF Planet Earth Limited | Wholesale & retail | 2022 |
| OFF the Wall (Cambridge) Limited | Construction | 2007 |
| Offbeat Music Limited | Information & communication | 2025 |
| Office Athletes (Cambridge) Ltd | Other services | 2017 |
| Office Crap PTY Ltd | Administrative & support | 2026 |
| Office Develop Ltd | Administrative & support | 2011 |
| Officeergo Innovations Ltd | Manufacturing | 2023 |
| Officina Publishing Services Ltd | Manufacturing | 2025 |
| Offord and Camp Limited | Construction | 2022 |
| Ogado Limited | Manufacturing | 2026 |
| Oggi Tomic Films Ltd | Information & communication | 2019 |
| Ogradena Limited | Health & social care | 2013 |
| OH Susannah International Limited | Administrative & support | 2025 |
| Ohizi Limited | Real estate | 2024 |
| Ohnbar Ltd | Information & communication | 2024 |
| OI! Monster Limited | Manufacturing | 2015 |
| OJ Jessica LLP | | 2022 |
| OJB Trading Limited | Wholesale & retail | 2024 |
| Ojmr Solutions Ltd | Construction | 2025 |
| OK Bargains Ltd | Wholesale & retail | 2019 |