| Nousi Tools Trading Limited | Extraterritorial | 2015 |
| Nova New Material Co., Ltd | Wholesale & retail | 2024 |
| Novalume Limited | Health & social care | 2025 |
| Novillo Engineering Limited | Professional & scientific | 2022 |
| Novus Estate Agent Limited | Real estate | 2023 |
| NRR Consulting Limited | Information & communication | 2026 |
| NS & AM Properties Limited | Real estate | 2016 |
| NS Mould International Ltd | Wholesale & retail | 2017 |
| Ntrs Limited | Wholesale & retail | 2008 |
| Ntsignals Ltd | Construction | 2023 |
| Nuac Capital Investments Ltd | Real estate | 2026 |
| Nuac Homes Limited | Real estate | 2015 |
| Nubole Limited | Extraterritorial | 2021 |
| Nucleus Education Ltd | Education | 2022 |
| Numico Limited | Extraterritorial | 2014 |
| Nurtr Digital Limited | Professional & scientific | 2025 |
| Nurturing Wild Ltd | Wholesale & retail | 2023 |
| Nutbrook Court Management Company Limited | Hospitality | 1990 |
| Nutriguard Natural Ltd | Wholesale & retail | 2025 |
| Nutriwave Limited | Extraterritorial | 2024 |
| Nuwa Music Ltd | Arts & recreation | 2026 |
| Nuxley Financial Services Ltd | Professional & scientific | 2017 |
| O & a Residential Limited | Real estate | 2013 |
| Oak Tree Day Nursery (London) Limited | Health & social care | 2004 |
| Oak Tree Montessori Limited | Health & social care | 2023 |
| Oakbury Building Services Ltd | Professional & scientific | 2015 |
| Oakdene Bromley Limited | Construction | 2018 |
| Oaklands (Beckenham) Residents' Association Limited | Households | 1968 |
| Oakley Cattery Hotel Limited | Agriculture & fishing | 2003 |
| Oakley Hair Academy Limited | Other services | 2016 |
| Oaks Electrical Services Ltd | Construction | 2021 |
| Oasis Home Deco Co., Ltd | Extraterritorial | 2013 |
| Oasis Marine Engineering Ltd | Extraterritorial | 2022 |
| Oasisbo Fabric Industry Company Limited | Extraterritorial | 2023 |
| Obaid E-Commerce Ltd | Wholesale & retail | 2026 |
| Obtain-Elec Limited | Manufacturing | 2011 |
| Obweus Limited | Professional & scientific | 2016 |
| Ocant Biological Technology Co., Ltd. | Professional & scientific | 2021 |
| Ocean GUY Marine Limited | Wholesale & retail | 2021 |
| Ocean Harmony Marine Service Limited | Extraterritorial | 2023 |
| Ocean Line Marine Service Co., Ltd | Manufacturing | 2025 |
| Ocean Perfect Group Limited | Agriculture & fishing | 2023 |
| Ocean Route Ship Store Co. Ltd | Extraterritorial | 2015 |
| Ocean Sailing Merchant Technology Co., Ltd | Manufacturing | 2021 |
| Oceana Marine Service Limited | Manufacturing | 2022 |
| Oceanchem Industrial Co., Limited | Wholesale & retail | 2016 |
| Oceanfood Sales Ltd | Extraterritorial | 2020 |
| Oceanheart Marine Service Co., Ltd | Manufacturing | 2025 |
| Oceanis Consulting Co., Ltd | Wholesale & retail | 2025 |
| Oceanlink Commerce Ltd. | Manufacturing | 2025 |
| Oceanwide Maritime Inspection Technology Co., Ltd | Manufacturing | 2023 |
| Oclean Care Technology (UK) Limited | Wholesale & retail | 2022 |
| OCR Holdings Limited | Financial services | 2025 |
| OCR Interims Limited | Administrative & support | 2025 |
| Octopus Industry Company Limited | Wholesale & retail | 2024 |
| Octrainbow Ltd | Wholesale & retail | 2024 |
| ODL Agency Limited | Professional & scientific | 2019 |
| Odsim Technology Limited | Manufacturing | 2021 |
| Odyssey AV Ltd | Manufacturing | 2018 |
| Odyssey Technology Cooperation Ltd | Extraterritorial | 2023 |
| Oelincom Technologies Ltd | Manufacturing | 2011 |
| Ofdiva Ltd | Manufacturing | 2024 |
| OG Commercial Glass Limited | Extraterritorial | 2015 |
| Ogrady Developments Ltd | Construction | 2021 |
| Ogun Property Investment Limited | Real estate | 2024 |
| Ogun Property Trading Limited | Real estate | 2022 |
| OH My Dog! Ltd | Hospitality | 2013 |
| OHM Art Limited | Professional & scientific | 2014 |
| Oiamoony UK Ltd | Manufacturing | 2023 |
| OIR Capital Limited | Financial services | 2026 |
| Okay Industry Limited | Wholesale & retail | 2015 |
| Oksana Senkevych Ltd | Information & communication | 2025 |
| Old Askean Social and Leisure Activities Limited | Professional & scientific | 1931 |
| Old Dunstonians Sports Club Limited | Arts & recreation | 1922 |
| Oleeya Industry Co., Ltd | Wholesale & retail | 2018 |
| Olek International Trade Co., Ltd. | Manufacturing | 2023 |
| Olima Beck Ltd | Hospitality | 2023 |
| Olireya Projects Limited | Administrative & support | 2006 |
| Olive's Beauty & Tanning Ltd | Other services | 2024 |
| Oliver Clothing Company Ltd | Wholesale & retail | 2025 |
| Ollie Birdi Properties LLP | | 2023 |
| Olympic Installations Limited | Manufacturing | 1992 |
| Omdi Group Co., Limited | Manufacturing | 2024 |
| Omega Services London Ltd | Wholesale & retail | 2014 |
| OMM Group Limited | Administrative & support | 2023 |
| Omni Corp Technology Limited | Information & communication | 2021 |
| Omniscient Publishing Limited | Information & communication | 2022 |
| On-Site.Socials Ltd | Professional & scientific | 2025 |
| One Clean Culture Ltd | Administrative & support | 2026 |
| One Decor Ltd | Wholesale & retail | 2026 |
| One DOT Four Ltd | Manufacturing | 2019 |
| One First Limited | Wholesale & retail | 2023 |
| One Link International Limited | Wholesale & retail | 2021 |
| One Mater of Sunshine Co., Limited | Wholesale & retail | 2021 |
| One Touch Physio Ltd | Health & social care | 2005 |
| One Tree Capital Ltd | Information & communication | 2021 |
| Onechimera Ltd | Construction | 2022 |
| Oneli Ltd | Manufacturing | 2016 |
| Oneworld International Foundation | Other services | 1999 |
| Only Home Appliances Ltd. | Extraterritorial | 2016 |