| Omni Fulfilment Ltd | Manufacturing | 2024 |
| Omni Management Ltd | Professional & scientific | 2023 |
| Omnis Design Limited | Professional & scientific | 2018 |
| Omnivision Monitoring Limited | Administrative & support | 2023 |
| Omoregie Healthcare Ltd | Administrative & support | 2016 |
| Omrum Limited | Administrative & support | 2022 |
| ON a Roll Flooring Ltd | Construction | 2014 |
| ON One Innovations Ltd | Professional & scientific | 2013 |
| ON Stage Solutions Ltd | Manufacturing | 2011 |
| ON the BUS Events Ltd | Arts & recreation | 2024 |
| ON Tour Films Ltd | Information & communication | 2021 |
| ON Track Business Support Ltd | Professional & scientific | 2021 |
| Onautm Ltd | Information & communication | 2025 |
| One 2 One Accountancy Solutions Ltd | Professional & scientific | 2011 |
| One 2 One Admin Services Ltd | Professional & scientific | 2019 |
| One Chens Ltd | Real estate | 2019 |
| One for ALL Hot Yoga Ltd | Arts & recreation | 2016 |
| One for the JOB Ltd | Manufacturing | 2024 |
| One Harmony 99 Ltd | Hospitality | 2018 |
| One Investment Projects Limited | Information & communication | 2017 |
| One Less Pill Ltd | Other services | 2019 |
| One One Hospitality 1 Limited | Real estate | 2023 |
| One One Hospitality Holdings Limited | Financial services | 2023 |
| One One Nine Specials Project Limited | Administrative & support | 2011 |
| One Shore Road Management Limited | Households | 2017 |
| One Step Outside Ltd | Professional & scientific | 2014 |
| One Stop DIY Timber Merchants Limited | Wholesale & retail | 2018 |
| One Surrey Road Management Company Limited | Households | 2005 |
| One Way Lettings Ltd | Real estate | 2020 |
| ONE2KEY Ltd | Information & communication | 2017 |
| ONE3SIX Group Ltd | Wholesale & retail | 2025 |
| Onebluebottle Ltd | Information & communication | 2026 |
| Onedp Ltd | Administrative & support | 2024 |
| Oneflow Drainage Ltd | Water & waste | 2024 |
| Onefuel Ltd | Manufacturing | 2025 |
| Onetogo Ltd | Information & communication | 2021 |
| Onform Group Limited | Professional & scientific | 2024 |
| Online Academies Limited | Education | 2018 |
| Online Showreels Limited | Arts & recreation | 2009 |
| Onshore Construction Limited | Construction | 2004 |
| Onshore Estates Limited | Construction | 2011 |
| Onshore Homes Ltd | Construction | 2002 |
| Onumsinachi & Co Ltd | Wholesale & retail | 2021 |
| Onyx Hair Limited | Other services | 2003 |
| Ookkee Holdings Ltd | Other services | 2021 |
| Ookkee Ltd | Other services | 2016 |
| Oort Cloud Trading Company Limited | Wholesale & retail | 2022 |
| OPA Coffee Limited | Hospitality | 2023 |
| OPA Combined Ltd | Wholesale & retail | 2024 |
| OPC Brickwork Ltd | Construction | 2017 |
| Open Advice Technologies Limited | Information & communication | 2021 |
| Open Comedy Ltd | Hospitality | 2020 |
| Openleaf Ltd | Professional & scientific | 2021 |
| Openzen Ltd | Construction | 2023 |
| Operational AI Marketing Systems Ltd | Wholesale & retail | 2026 |
| Ophir Management (Bournemouth) Limited | Households | 1991 |
| OPI Match Ltd | Wholesale & retail | 2016 |
| Oppenheim Estate Ltd | Real estate | 2023 |
| Oppi Technology Limited | Information & communication | 2023 |
| OPS Force One Limited | Professional & scientific | 2026 |
| Opti-It Limited | Information & communication | 2022 |
| Optima Search - Europe & America Limited | Administrative & support | 2013 |
| Optima Vehicle Transportation Limited | Construction | 2016 |
| Optimal Health Nutrition Ltd | Health & social care | 2020 |
| Optimal Property Limited | Construction | 2017 |
| Optimise Global Ltd | Information & communication | 2022 |
| Optimise Itsm Limited | Information & communication | 2024 |
| Optimum Chiropractic Clinic Ltd | Health & social care | 2024 |
| Optimum Dynamic Care Ltd | Health & social care | 2023 |
| Optimum Dynamic Properties Ltd | Real estate | 2025 |
| Optmis Ltd | Wholesale & retail | 2010 |
| Opulence by Dionne Ltd | Other services | 2020 |
| OPW Management Poole Ltd | Households | 2023 |
| OR Timepieces Ltd | Manufacturing | 2025 |
| Oracle Protection Insurance Brokers Ltd | Financial services | 2023 |
| Orange Housing Ltd | Real estate | 2020 |
| Orange Rooms Bournemouth Limited | Real estate | 2012 |
| Orasis Medical Limited | Health & social care | 2018 |
| Orbit 360 Food and Caterers Limited | Administrative & support | 2016 |
| Orbit 360 Ltd | Administrative & support | 2013 |
| Orbit Retails Limited | Wholesale & retail | 2011 |
| Orbit Technologies South Limited | Information & communication | 1990 |
| Orca Construction Ltd | Construction | 2018 |
| Orca Limited | Real estate | 2021 |
| Orchard Glen Management Limited | Households | 1999 |
| Orchard Properties Southern Limited | Real estate | 2022 |
| Orchardleigh Park Management Limited | Households | 1988 |
| Orchards Flat Management Company Limited(The) | Households | 1986 |
| Orchid Thai Massage and Spa Limited | Other services | 2020 |
| Orcn Solutions Limited | Information & communication | 2025 |
| Ordernizers Limited | Extraterritorial | 2016 |
| Orea Clinic Ltd | Other services | 2026 |
| Organ Factory Ltd | Real estate | 2024 |
| Organic Childcare Limited | Other services | 2015 |
| Oriade Limited | Public administration | 2020 |
| Oriental Bubble Tea Ltd | Wholesale & retail | 2020 |
| Oriental Express Food Catering Limited | Hospitality | 2011 |
| Oriental Rotisserie Ltd | Hospitality | 2025 |
| Oriental Style Ltd | Manufacturing | 2001 |
| Origin Barbecue Limited | Hospitality | 2026 |