| One for Groundwork’S Ltd | Construction | 2022 |
| One Group Customer Sport Ltd | Wholesale & retail | 2022 |
| One Group Dynamics Ltd | Professional & scientific | 2026 |
| One Group Engineering Limited | Professional & scientific | 2016 |
| One Group Racing Ltd | Professional & scientific | 2022 |
| One Health Lewisham Limited | Health & social care | 2016 |
| One Hood Street Northampton Management Company Limited | Real estate | 2005 |
| One in a Million Entertainment Ltd | Arts & recreation | 2005 |
| One Key Mortgages Ltd | Financial services | 2025 |
| One Louder Recordings Ltd | Arts & recreation | 2011 |
| One More Ting Caribbean Kitchen Ltd | Hospitality | 2015 |
| One Night in Bath Ltd | Information & communication | 2016 |
| One Place Affordable Housing Solutions Ltd | Professional & scientific | 2020 |
| One Safety Team Group Limited | Administrative & support | 2019 |
| One Step Consulting Limited | Professional & scientific | 2025 |
| One Stop Builders Merchants Limited | Wholesale & retail | 2007 |
| One Stop Consultancy Ltd | Professional & scientific | 2025 |
| One to One Design Studio Ltd | Information & communication | 2020 |
| One Vision Alliance Limited | Financial services | 2021 |
| One Woodland Limited | Real estate | 2017 |
| One World Alliance Recruitment Group Ltd | Administrative & support | 2022 |
| One&Only Healthcare Services Ltd | Health & social care | 2022 |
| One-Time Solutions Ltd | Water & waste | 2021 |
| Onedb Limited | Professional & scientific | 2013 |
| Onediary Ltd | Information & communication | 2026 |
| Onefoursix Limited | Information & communication | 2011 |
| Oneira Developments Limited | Professional & scientific | 2006 |
| Onemsp Limited | Information & communication | 2016 |
| Oneplanit Limited | Professional & scientific | 2014 |
| Onereg Ltd | Wholesale & retail | 2024 |
| Onetik Limited | Professional & scientific | 2019 |
| Oneway (Essex) Limited | Construction | 2017 |
| Ongp Limited | Hospitality | 2021 |
| Oniscenko Ltd | Transport & logistics | 2017 |
| Online Automotive Limited | Wholesale & retail | 2006 |
| Online Company Formations Limited | Professional & scientific | 2019 |
| Online Conveyancing Quote Limited | Information & communication | 2010 |
| Online Direct Limited | Energy | 1998 |
| Online Merch Seller Ltd | Wholesale & retail | 2025 |
| Online REC Limited | Professional & scientific | 2025 |
| Online Trading Advisors Limited | Professional & scientific | 2025 |
| Onlyyou Designs Limited | Manufacturing | 2021 |
| Onpoint Fulfilment Limited | Transport & logistics | 2020 |
| Onr.Construct Limited | Construction | 2025 |
| Onroad Mobile Tyres Ltd | Wholesale & retail | 2025 |
| Onsite Hydraulics Ltd | Manufacturing | 2023 |
| Ontam Ltd | Wholesale & retail | 2021 |
| Ontarget Range Limited | Arts & recreation | 2014 |
| Onxy Care and Counselling Limited | Health & social care | 2025 |
| Onyourmarks Athletics Ltd | Arts & recreation | 2026 |
| Onyx 4X4 Ltd | Manufacturing | 2022 |
| Onyx Estates Ltd | Real estate | 2021 |
| Ooberfit Limited | Information & communication | 2019 |
| Oodles Works Limited | Construction | 2019 |
| Ooid Ltd | Transport & logistics | 2026 |
| Oonice Services Company Ltd | Administrative & support | 2025 |
| OP Ventilations System Ltd | Construction | 2019 |
| Opal Consultancy Solutions Limited | Professional & scientific | 2025 |
| Opal Court Holdings Limited | Financial services | 2025 |
| Opal Court Property Services Limited | Real estate | 2018 |
| Opal Property Solutions Limited | Real estate | 2025 |
| Open Air Hire Limited | Health & social care | 2014 |
| Open Delivery Limited | Information & communication | 2021 |
| Open Doors Care Limited | Health & social care | 2023 |
| Open House New Forest Ltd | Hospitality | 2024 |
| Open House Pubco Ltd | Hospitality | 2024 |
| Open Reality Limited | Information & communication | 1999 |
| Open Space (Uppingham) Management Company Limited | Real estate | 2017 |
| Open Stage Performing Arts Company Ltd. | Arts & recreation | 2013 |
| Operation Seraphim Limited | Information & communication | 2010 |
| Operonix Ltd | Information & communication | 2021 |
| Opg.Beauty Limited | Administrative & support | 2025 |
| Ophelia Employment Partners Ltd | Wholesale & retail | 2018 |
| Opportunities UN Ltd | Transport & logistics | 2011 |
| Oprate Ltd | Information & communication | 2026 |
| Oprint Limited | Manufacturing | 2008 |
| Optavia Ltd | Arts & recreation | 2025 |
| Optibloom Nutrition Limited | Wholesale & retail | 2026 |
| Optic Capital Limited | Construction | 2025 |
| Optic Homes Limited | Construction | 2025 |
| Optical Sciences Limited | Administrative & support | 1995 |
| Optilinksplice Ltd | Information & communication | 2024 |
| Optimal Precision Engineering Limited | Professional & scientific | 2024 |
| Optimal Rehabilitation Limited | Other services | 2020 |
| Optimax Holdings Ltd | Financial services | 2020 |
| Optimising Project Delivery Ltd | Professional & scientific | 2018 |
| Optimum Alldrive Ltd | Administrative & support | 2014 |
| Optimum Asset Ltd | Financial services | 2019 |
| Optimum Careers Limited | Professional & scientific | 2018 |
| Optimum Consulting Global Ltd | Information & communication | 2019 |
| Optimum Land Asset Ltd | Real estate | 2014 |
| Optimum Management Consulting Limited | Information & communication | 2016 |
| Optimum Medical Group Ltd | Health & social care | 2015 |
| Optimus 7 Solutions Ltd | Professional & scientific | 2021 |
| Option 7 Consulting Ltd | Professional & scientific | 2018 |
| Optix Company UK Limited | Manufacturing | 2002 |
| Opulent Africa Limited | Administrative & support | 2016 |
| Opulent Travel Group Limited | Administrative & support | 2008 |
| Opus Decoration & Interiors Ltd | Professional & scientific | 2018 |
| Opus Hair Limited | Other services | 2013 |