| North London Mikvah Limited | Other services | 2010 |
| North London Private Hire Limited | Transport & logistics | 2012 |
| North Sea Fish & Chips Ltd | Extraterritorial | 2024 |
| North Sea Fish (London) Ltd | Extraterritorial | 2024 |
| North Sea Fish Restaurant Ltd | Extraterritorial | 2024 |
| Northaw Transition CIC | Other services | 2011 |
| Northstar Land Limited | Real estate | 1996 |
| Northstar Property Investment Limited | Real estate | 1996 |
| Nostaljik Ltd | Manufacturing | 2020 |
| Nova Aetas Ltd | Real estate | 2020 |
| Nova Natural Health Ltd | Health & social care | 2017 |
| Nova Portfolio Ltd | Real estate | 2026 |
| Novella London Limited | Wholesale & retail | 2021 |
| Novena Consulting Limited | Financial services | 2016 |
| NP Advanced Skin Clinic Ltd | Other services | 2026 |
| NPD Consulting Ltd | Professional & scientific | 2020 |
| NR Music Management & Consultantcy Ltd. | Information & communication | 2017 |
| NRG Environmental Ltd | Water & waste | 2016 |
| NS Electrofuture Limited | Professional & scientific | 2018 |
| NSB Care Ltd | Health & social care | 2019 |
| NSR Physiotherapy Limited | Health & social care | 2026 |
| Nubian Delivery Services Ltd | Transport & logistics | 2020 |
| Nucore Construction Ltd | Construction | 2018 |
| Nucore Construction Services Limited | Construction | 2021 |
| Nucore Developments Limited | Construction | 2025 |
| Nueva Investments | Financial services | 2024 |
| Nueva Realty (UK) Limited | Real estate | 2014 |
| Nugent Groundworks Limited | Other services | 2019 |
| Number One Accounting Ltd | Professional & scientific | 2025 |
| Numbers Associates Ltd | Professional & scientific | 2007 |
| Numbers Management Consultancy Ltd | Professional & scientific | 2018 |
| Nursery Fields Management Limited | Households | 1984 |
| Nursery Freehold Limited | Households | 2005 |
| Nutrifull Limited | Wholesale & retail | 2025 |
| NW London Electrician Ltd | Construction | 2026 |
| Nyadowa Homes Ltd | Real estate | 2023 |
| O E Production Limited | Administrative & support | 2015 |
| O Obaro and Sons Limited | Professional & scientific | 2016 |
| O T Construction Ltd | Construction | 2012 |
| O&F Associates Ltd | Information & communication | 2025 |
| O'Hanlon Property Limited | Real estate | 2019 |
| Oak Vets Ltd | Professional & scientific | 2024 |
| Oakbank Estates Limited | Real estate | 2007 |
| Oakcourt (Freehold) Limited | Households | 1996 |
| Oakfield Tours Limited | Administrative & support | 1983 |
| Oakmace Events Ltd | Administrative & support | 2020 |
| Oakmere Youth and Community Centre | Arts & recreation | 2002 |
| Oakmoss Limited | Manufacturing | 1977 |
| Oaks Funeral Directors Ltd | Other services | 2024 |
| Oakside Management Ltd | Real estate | 2018 |
| Oakwall Holdings Ltd | Administrative & support | 2026 |
| Oakwell Place 2 Management Limited | Households | 2026 |
| Oakwood Developers Limited | Construction | 2022 |
| Oaky the Brand Limited | Wholesale & retail | 2025 |
| Oasis International Investments Ltd | Construction | 2015 |
| Obcom Limited | Administrative & support | 2006 |
| OBI 1WAY Ltd | Education | 2026 |
| Ocean Preserve Limited | Manufacturing | 2018 |
| Oceanwide Holdings Limited | Other services | 2017 |
| OCL Logistic Ltd | Wholesale & retail | 2021 |
| Octavius Homes Ltd | Financial services | 2021 |
| OE & B Ltd | Health & social care | 2023 |
| OFF the Ground Solutions Ltd | Professional & scientific | 2020 |
| Offer UP TV Ltd | Information & communication | 2015 |
| OG Decorating Ltd | Construction | 2024 |
| Ohana Growth HR Consultancy Ltd | Administrative & support | 2025 |
| OJC Search Limited | Administrative & support | 2023 |
| OJL Construction Ltd | Construction | 2025 |
| Okalio Finance & Investments Limited | Professional & scientific | 2017 |
| Old Owen's Association and Sports Club Limited | Arts & recreation | 2014 |
| Old Park Farm (Hertfordshire) Limited | Real estate | 1998 |
| Olexa Limited | Construction | 2025 |
| Olimasuk Ltd | Manufacturing | 2025 |
| Olive & Rose Ltd | Construction | 2025 |
| Olive Tree Designs Ltd | Professional & scientific | 2020 |
| Olympic Preservation Limited | Manufacturing | 2015 |
| Olyve Property Group Limited | Real estate | 2024 |
| Omeco Group Ltd | Administrative & support | 2024 |
| Omega Fashions Limited | Manufacturing | 2013 |
| Omega Resistance Wire Limited | Extraterritorial | 2011 |
| Omega Wire Limited | Manufacturing | 2007 |
| Omni Partnership Ltd | Administrative & support | 2021 |
| ON & Offline Services Limited | Information & communication | 2008 |
| ON Rotation Beauty and Wellness Ltd | Other services | 2025 |
| ON Solid Ground Services Ltd | Information & communication | 2026 |
| OND Properties Limited | Real estate | 2025 |
| One Call Appliance (London) Limited | Wholesale & retail | 2016 |
| One Flooring Ltd | Construction | 2019 |
| One Hundred & Five Gloucester Terrace Management Limited | Households | 1968 |
| One Stop Allterrain Shop Limited | Other services | 2018 |
| One the Band UK Ltd | Arts & recreation | 2018 |
| One Time Care Limited | Public administration | 2022 |
| ONE2ONE First Responder Training Ltd | Administrative & support | 2021 |
| Onestop Gearbox Shop Limited | Other services | 2017 |
| Onsite Development Management Limited | Administrative & support | 2015 |
| Onwine Limited | Administrative & support | 2001 |
| Ookami Limited | Information & communication | 2020 |
| OP10 Place Ltd | Hospitality | 2024 |
| Opal Cherry Limited | Information & communication | 2017 |
| Opal Stone Investments Ltd | Real estate | 2025 |