| NP9 Investments Limited | Real estate | 2017 |
| NPS (Walmer) Limited | Real estate | 2025 |
| NPS Property (Gillingham) Limited | Real estate | 2012 |
| NPS Property (Watford) Limited | Real estate | 2015 |
| NPS Property (Witham) Limited | Real estate | 2012 |
| NPS Property Enfield Limited | Real estate | 2014 |
| NPS Property Holding Limited | Real estate | 2012 |
| NR Prime Group Ltd | Real estate | 2026 |
| Nrex Cleaners Ltd | Administrative & support | 2023 |
| NRI Legal Services Ltd | Administrative & support | 2012 |
| NSA Properties Ltd | Real estate | 2024 |
| NSN 1 Limited | Health & social care | 2023 |
| NU Sourcing Ltd | Manufacturing | 2013 |
| Nuforce Ltd | Education | 2024 |
| Nuga Care Services Limited | Health & social care | 2025 |
| Nugadel Limited | Transport & logistics | 2026 |
| Nuha Ltd | Wholesale & retail | 2020 |
| Numie Properties Ltd | Administrative & support | 2012 |
| Numinus Ltd | Administrative & support | 2021 |
| Nunestra Limited | Health & social care | 2025 |
| Nuova Immobiliare 2015 Ltd | Financial services | 2020 |
| Nuro Limited | Other services | 2016 |
| Nurture Finance Limited | Financial services | 2025 |
| NURTURE4 Limited | Health & social care | 2025 |
| Nutrapad Ltd | Wholesale & retail | 2024 |
| Nutrinnovation Limited | Hospitality | 2012 |
| NV Builders Limited | Real estate | 1997 |
| NV Smart Homes Ltd | Information & communication | 2017 |
| NVD Enterprises Limited | Real estate | 2020 |
| NVJ UK Limited | Real estate | 2020 |
| NW Housing Ltd | Real estate | 2016 |
| Nwando Care Limited | Health & social care | 2012 |
| Nwando Properties Ltd | Real estate | 2022 |
| Nxtin Limited | Wholesale & retail | 2024 |
| Nyakoe Holdings Limited | Financial services | 2025 |
| Nyakoe Ltd | Information & communication | 2023 |
| Nyakoe-Property Ltd | Real estate | 2024 |
| NZ Solutions Limited | Construction | 2012 |
| NZ Utilities Ltd | Construction | 2025 |
| O R Developments Ltd | Construction | 2024 |
| O'Brien Plumbing Limited | Other services | 2011 |
| O'Connell Plant Hire Limited | Construction | 2017 |
| O'Hagan Contracts Limited | Construction | 2011 |
| O'Hagan London Ltd | Construction | 2022 |
| OA Management Limited | Professional & scientific | 2020 |
| Oagi Ltd. | Wholesale & retail | 2018 |
| Oak Estates Management Limited | Extraterritorial | 2015 |
| Oakdell Investments Limited | Real estate | 2014 |
| Oakseal 1 Limited | Extraterritorial | 2017 |
| Oakseal 2 Limited | Extraterritorial | 2017 |
| Oakseal 3 Limited | Extraterritorial | 2017 |
| Oakseal Ltd. | Professional & scientific | 2013 |
| Oaktree Venture Capital Ltd | Administrative & support | 2023 |
| Oakwood Technology Limited | Information & communication | 1994 |
| Oasis India Advisory Group Ltd | Professional & scientific | 2024 |
| Oats Investments Limited | Real estate | 2024 |
| Objective Journalism Ltd | Information & communication | 2024 |
| OBK Clothing Limited | Wholesale & retail | 2018 |
| Obsgyn London Ltd | Health & social care | 2019 |
| Ocds Healthcare Limited | Health & social care | 2023 |
| Oceanforce Limited | Other services | 2023 |
| Ocha Group Ltd | Real estate | 2020 |
| OD Softech Limited | Information & communication | 2021 |
| Oddjob Events Ltd | Arts & recreation | 2026 |
| Odes Limited | Other services | 2006 |
| OFC Property Limited | Real estate | 2024 |
| OFD Group Ltd | Wholesale & retail | 2026 |
| Offeriing Ltd | Wholesale & retail | 2026 |
| Office Power Products Limited | Wholesale & retail | 2011 |
| Office Products Online Limited | Wholesale & retail | 2013 |
| Ogconsult Ltd | Professional & scientific | 2022 |
| Oh-Ho Ltd | Information & communication | 2021 |
| OHN MAR WIN Limited | Arts & recreation | 2017 |
| Ojasvin Limited | Administrative & support | 2017 |
| Okehampton Ltd | Real estate | 2019 |
| Okolotowicz Trading Ltd | Real estate | 2012 |
| Oladimeji Prestige & Co. Ltd | Professional & scientific | 2024 |
| Olala Global Ltd | Wholesale & retail | 2025 |
| Oland Developments Limited | Construction | 2022 |
| Old Chiswick Yard Management Company Limited | Real estate | 1999 |
| Old Cottage Chichester Limited | Hospitality | 2017 |
| Old Forge Farm Ltd | Real estate | 2025 |
| Oldercare Limited | Extraterritorial | 2010 |
| Oleander Limited | Professional & scientific | 2002 |
| Oliver Industries Ltd | Information & communication | 2009 |
| Oliver James Productions Limited | Information & communication | 1987 |
| Olliffe Street Residents Association Limited | Households | 2000 |
| Olmeqa Limited | Information & communication | 2023 |
| Olym-Fitness Limited | Arts & recreation | 2022 |
| OM Mobile Ventures (UK) Limited | Information & communication | 2019 |
| OM Shiv Trading Limited | Wholesale & retail | 2024 |
| Omarzai Ltd | Real estate | 2024 |
| Omdot Limited | Information & communication | 2026 |
| Omega Court RTM Company Limited | Households | 2020 |
| Omega Guarding Limited | Administrative & support | 2011 |
| Omega Realisations Ltd | Financial services | 2012 |
| Omene Homes Ltd | Real estate | 2019 |
| Omhaven Limited | Wholesale & retail | 1990 |
| Omizz Ltd | Hospitality | 2019 |
| Omni Consulting Solutions Limited | Information & communication | 2018 |