| NSG & Co UK Ltd | Administrative & support | 2020 |
| NSL 247 Limited | Administrative & support | 2015 |
| NSM 1 Contractors Ltd | Construction | 2022 |
| NSM Management Consultancy Limited | Professional & scientific | 2014 |
| NSP Europe Limited | Professional & scientific | 1993 |
| NSS Industries Ltd | Financial services | 2022 |
| Nssl Group Ltd | Public administration | 2023 |
| Nssl Holding Ltd | Health & social care | 2022 |
| Nstyle Ltd | Manufacturing | 2021 |
| NT Packaging Ltd | Wholesale & retail | 2017 |
| Nuances Clinical Consultancy Ltd | Professional & scientific | 2021 |
| Nucleus of Change Limited | Professional & scientific | 2008 |
| Nugent Couriers LLP | | 2020 |
| Nuges Consulting Limited | Professional & scientific | 2016 |
| Nuitee UK Ltd | Information & communication | 2024 |
| Nuland Court RTM Company Ltd | Real estate | 2015 |
| Nulla Nulla Capital Advisors Ltd | Professional & scientific | 2013 |
| Number Fourteen (Management) Limited | Real estate | 2013 |
| Number Fourteen (Trading) Limited | Hospitality | 2014 |
| Numeritas Ltd | Professional & scientific | 2003 |
| Numonas Limited | Households | 1977 |
| NUR Structures LLP | | 2011 |
| Nurture & Harmony Healthcare Ltd | Health & social care | 2020 |
| Nurturing Young Knowledge and Growth Limited | Education | 2025 |
| Nutriwonder Ltd. | Wholesale & retail | 2019 |
| Nutter Road Limited | Professional & scientific | 2025 |
| NW Education and Facilities Management Limited | Education | 2016 |
| NWL Development Ltd | Construction | 2024 |
| NWL Properties Ltd | Real estate | 2024 |
| NX Consultancy Ltd | Professional & scientific | 2023 |
| NYA Events Ltd | Arts & recreation | 2019 |
| Nyami Deluxe Painting & Decorating Limited | Extraterritorial | 2024 |
| NYK Accessories Limited | Wholesale & retail | 2009 |
| NYK Wedding Ltd | Wholesale & retail | 2011 |
| Nyla Investments Ltd | Other services | 2020 |
| NZA Food Centre Ltd | Wholesale & retail | 2026 |
| O Lawal Company Ltd | Health & social care | 2016 |
| O&A Homes Holding Limited | Financial services | 2025 |
| O&S Contractors Ltd | Construction | 2025 |
| O'Connell Carpentry & Building Ltd | Construction | 2019 |
| O'Hagan Transport Limited | Transport & logistics | 2001 |
| O'Hagan Transportation Ltd | Transport & logistics | 2015 |
| O'West Ventures Ltd | Real estate | 2021 |
| O'Zone Communications Limited | Professional & scientific | 1997 |
| O.C.S. Consulting (EOT) Limited | Administrative & support | 2023 |
| O.S Electrical Ltd | Construction | 2023 |
| Oak Glade Epsom Limited | Construction | 2024 |
| Oak Hill Dental Practice Limited | Health & social care | 2024 |
| Oak Lawn Compton Limited | Construction | 2023 |
| Oakdene Heating Ltd | Other services | 2009 |
| Oakfield (Foods) Limited | Manufacturing | 1987 |
| Oakfield Food Group Limited | Financial services | 2024 |
| Oakhilltoday Ltd | Real estate | 2015 |
| Oakleigh Retail Group Limited | Wholesale & retail | 2019 |
| Oaklucent Ltd | Information & communication | 2025 |
| Oakridge (Willenhall) Management Company Limited | Households | 2004 |
| Oakside Holdings Ltd | Financial services | 2026 |
| Oaktree Homecare Services Limited | Health & social care | 2018 |
| Oakview Close Management Company Limited | Households | 2003 |
| Oakvine Furniture Limited | Construction | 2012 |
| Oakwell Grange Management Company Limited | Households | 2015 |
| Oana Nechifor Ltd | Information & communication | 2023 |
| Oanady Limited | Transport & logistics | 2024 |
| Oasis Medspa Limited | Other services | 2023 |
| OAT House RTM Company Limited | Households | 2020 |
| Obic UK | Other services | 2020 |
| Oblidah Limited | Administrative & support | 2017 |
| Oceanicoasisdeals Limited | Wholesale & retail | 2023 |
| OCS Cash Management Solutions Limited | Information & communication | 2008 |
| OCS Solutions Limited | Professional & scientific | 2016 |
| Octamax Limited | Professional & scientific | 2023 |
| Octi Lock Ltd | Manufacturing | 2019 |
| Octoplas Traders Limited | Administrative & support | 1999 |
| Oculus Consultancy Limited | Health & social care | 2020 |
| Oddmans Limited | Professional & scientific | 2018 |
| Odelay Ltd | Information & communication | 2011 |
| Odin Sense Ltd | Information & communication | 2024 |
| Oecm Investments Limited | Real estate | 2025 |
| OEJ Investments Limited | Administrative & support | 2018 |
| Offtape Limited | Information & communication | 2013 |
| OGA Design and Build Ltd | Construction | 2023 |
| OGP Consultancy Limited | Professional & scientific | 2020 |
| Ogunro Ltd | Health & social care | 2024 |
| OGW Investment Holdings LP | | 2024 |
| Ogwih LLP | | 2024 |
| OH My COD 2026 Ltd | Hospitality | 2026 |
| Ohsocute Limited | Wholesale & retail | 2023 |
| Oink Media Limited | Other services | 2017 |
| Okobin Ltd | Health & social care | 2014 |
| OKP1 Limited | Hospitality | 2021 |
| Old Castle Productions Limited | Information & communication | 2024 |
| Old Hatchet Ascot Ltd | Hospitality | 2022 |
| Old Hatchet Winkfield Ltd | Hospitality | 2023 |
| Old House Gardens RTM Company Limited | Households | 2013 |
| Olive Plumbing and Heating Ltd | Construction | 2012 |
| Oliver Miller Interiors Ltd | Professional & scientific | 2022 |
| Oliver Tebbutt Creative Ltd | Arts & recreation | 2024 |
| Olivia Grace Jewellery Limited | Other services | 2014 |
| Olulola Ltd | Professional & scientific | 2019 |
| OM Hire Ltd | Administrative & support | 2021 |