| Oaks Car Limited | Other services | 2021 |
| Oaks Close (Tonbridge) Management Company Limited | Real estate | 2010 |
| Oaks Energy Advisory Ltd | Professional & scientific | 2015 |
| Oakspring (HR) Limited | Administrative & support | 2020 |
| Oakspring Limited | Hospitality | 2020 |
| Oakwood Holdco Limited | Financial services | 2024 |
| Oakwood Wild Estates Ltd | Real estate | 2024 |
| Oasis Developments (South East) Limited | Construction | 2021 |
| Oast Gardens Management Company Limited | Households | 2022 |
| Oast House Holdings Limited | Financial services | 2017 |
| Oast View Bodiam Limited | Real estate | 2020 |
| OBE & Co Design Limited | Manufacturing | 2012 |
| Obisol Group Ltd | Professional & scientific | 2024 |
| Obsessed Studios Limited | Information & communication | 2026 |
| Obvara Ltd | Information & communication | 2024 |
| Occam Analytics Limited | Information & communication | 2017 |
| Ocean Hippy Holdings International Limited | Financial services | 2023 |
| Ocean House Property Management Limited | Households | 2009 |
| Octamis Consulting Limited | Information & communication | 2018 |
| Octamis Limited | Information & communication | 2016 |
| Octopus Metrics Ltd. | Professional & scientific | 2018 |
| Octopus Think Ltd | Information & communication | 2019 |
| Oculus Consulting Ltd | Professional & scientific | 2001 |
| OD Design Limited | Professional & scientific | 2023 |
| Odyssey (UK) Limited | Extraterritorial | 2013 |
| Odyssey Design & Build Ltd | Construction | 2018 |
| OEZ Limited | Hospitality | 2024 |
| OFF the Hanger Wholesale Limited | Wholesale & retail | 2022 |
| OFF World Media Limited | Information & communication | 2016 |
| Office Square Management Limited | Hospitality | 2000 |
| Officetribe 2 Limited | Real estate | 2021 |
| Officetribe Ltd | Real estate | 2018 |
| Ohana Ventures Ltd | Health & social care | 2014 |
| Ohbo Properties Limited | Real estate | 2025 |
| Oilstone Consulting Limited | Professional & scientific | 2013 |
| Oink and Outfit Ltd | Professional & scientific | 2024 |
| Ojgf Limited | Administrative & support | 2024 |
| OKC Consulting Limited | Professional & scientific | 2018 |
| Okoye Ltd | Health & social care | 2009 |
| OLA Ents Ltd | Professional & scientific | 2024 |
| OLA Investments Limited | Real estate | 2018 |
| Old Dairy Brewery Limited | Manufacturing | 2009 |
| Old Dogs New Media Ltd | Information & communication | 2026 |
| Old Fire Station Flats Management Company Limited | Real estate | 2015 |
| Old Hunstanton Coach House Mews Management Company Limited | Households | 2008 |
| Old Park Land Limited | Real estate | 2023 |
| Oldburn LLP | | 2016 |
| Olden Property Consulting Limited | Professional & scientific | 2014 |
| Oleah Consulting Ltd | Professional & scientific | 2023 |
| Olen Solutions Limited | Professional & scientific | 2017 |
| Olisa Developments Ltd | Construction | 2025 |
| Olisa Estates Ltd | Real estate | 2026 |
| Olisop Group Limited | Real estate | 2019 |
| Olisop Investments SPV Limited | Real estate | 2018 |
| Olisop Investments SPV One Limited | Real estate | 2021 |
| Olivelle Limited | Wholesale & retail | 2024 |
| Oliver Bowater Construction Limited | Construction | 2024 |
| Olivia Thornhill Ltd | Professional & scientific | 2022 |
| Olympia Europe Travel Agency Limited | Administrative & support | 1995 |
| OM Carpentry and Joinery Limited | Manufacturing | 2014 |
| OM Selection Ltd | Professional & scientific | 2018 |
| OMB Tax Limited | Professional & scientific | 2003 |
| Omcap Limited | Financial services | 1989 |
| Omdir Limited | Hospitality | 2025 |
| Omfinia Ltd | Information & communication | 2020 |
| Omky Group Limited | Information & communication | 2018 |
| Omky Studios Ltd | Information & communication | 2017 |
| Omni Recycled Materials Limited | Water & waste | 2012 |
| Omni Recycling Limited | Water & waste | 2015 |
| OMT Consultancy Ltd | Professional & scientific | 2013 |
| ON Brand on Ltd | Professional & scientific | 2023 |
| ON the DOT Business Management Ltd | Professional & scientific | 2022 |
| ON the DOT Counts Ltd | Professional & scientific | 2025 |
| On-Level Paving Limited | Construction | 1998 |
| Onajobi Group Limited | Health & social care | 2020 |
| Onboard Executive Ltd | Professional & scientific | 2015 |
| One 2 One Deco Limited | Construction | 1981 |
| One and ALL Financial Services Ltd | Financial services | 2014 |
| One Britan Ltd | Wholesale & retail | 2024 |
| One Clavdivs Limited | Hospitality | 2023 |
| One Delivery BNH Ltd | Hospitality | 2019 |
| One Eighty Degrees Ltd | Information & communication | 2025 |
| One QR Management Company Limited | Extraterritorial | 2015 |
| One Stop VA Ltd | Administrative & support | 2023 |
| One. Aesthetics 89A Ltd | Other services | 2023 |
| Online Beauty Courses Worldwide Ltd | Other services | 2024 |
| Only Tradies Ltd | Construction | 2024 |
| Onyx Software Limited | Information & communication | 1995 |
| Onyx Source Ltd | Wholesale & retail | 2019 |
| Oonst Limited | Information & communication | 2013 |
| Opal Property Investment Limited | Real estate | 2018 |
| Opalle Ltd | Information & communication | 2025 |
| Openiris Ltd | Information & communication | 2021 |
| Openpatho Ltd | Information & communication | 2023 |
| Opio Inc Limited | Information & communication | 2026 |
| Opsify Limited | Information & communication | 2019 |
| Opt-In Lifestyle Ltd | Manufacturing | 2021 |
| Optimum (GB) Limited | Professional & scientific | 2009 |
| Optimytics Limited | Information & communication | 2021 |
| Optivisee Ltd | Professional & scientific | 2026 |