| N.R. Spraying Limited | Agriculture & fishing | 2006 |
| N.Y. Productions Limited | Professional & scientific | 2004 |
| N21 Electrical Services Ltd | Manufacturing | 2025 |
| N9 Projects Ltd | Professional & scientific | 2025 |
| Nagson Limited | Information & communication | 1999 |
| Nama Estate Ltd | Real estate | 2023 |
| Nanotek Limited | Administrative & support | 1999 |
| Napier 3 Ltd | Transport & logistics | 2023 |
| Narrative Leadership Limited | Professional & scientific | 2007 |
| Nasty Limited | Wholesale & retail | 2025 |
| National Gymnastics Association UK Ltd | Arts & recreation | 2025 |
| Natural Investments Limited | Real estate | 2000 |
| Naturality Limited | Health & social care | 1991 |
| NB Property Collective Ltd | Real estate | 2026 |
| Neal Display Limited | Manufacturing | 2002 |
| Neale Property Services Limited | Real estate | 2006 |
| Need One Soon Limited | Construction | 2006 |
| Neil James & Co Limited | Professional & scientific | 2003 |
| NEK Family Limited | Education | 2016 |
| Nellben Limited | Health & social care | 2005 |
| Nellsar Limited | Health & social care | 1999 |
| Neptune Aviation Services Limited | Professional & scientific | 2003 |
| Netherdown (Herts) Limited | Construction | 1994 |
| Netinvestments.Io Limited | Financial services | 2017 |
| New Century Contract Cleaning Services Ltd. | Administrative & support | 1999 |
| New Lantern House 2018 Ltd | Hospitality | 2018 |
| New Media AID Limited | Information & communication | 2000 |
| New World Reefers Limited | Other services | 2002 |
| Newcare Group Limited | Wholesale & retail | 1983 |
| Newland Bros (Construction) Limited | Construction | 1971 |
| Newman Safety Services Limited | Professional & scientific | 2003 |
| Newmill Holdings Limited | Professional & scientific | 2003 |
| Newsprinters Holdings Limited | Information & communication | 2023 |
| Nexit Limited | Hospitality | 2006 |
| NH Property Consultants Ltd | Real estate | 2006 |
| Nicholsons Accountancy Services Limited | Professional & scientific | 1999 |
| Nicosia Car Parks Ltd | Transport & logistics | 2025 |
| Nicosia Finance Ltd | Financial services | 2025 |
| Nicosia Holdings Ltd | Financial services | 2025 |
| Nigella Express Limited | Manufacturing | 2007 |
| Nobilla Machine Tools Limited | Manufacturing | 2007 |
| Noble Properties Group Ltd | Real estate | 2019 |
| Nockolds LLP | | 2007 |
| Nomad Consulting Limited | Professional & scientific | 1996 |
| Nomtrad Limited | Professional & scientific | 2003 |
| Noonar DP Limited | Health & social care | 2011 |
| Normanton Mews Ltd | Extraterritorial | 2020 |
| Norsewood Kitchen Centre Limited | Other services | 1993 |
| Nortech & Co. LP | | 2002 |
| Nortech Engineering Services Limited | Manufacturing | 2001 |
| North London SAW Works Limited(The) | Manufacturing | 1943 |
| Northridge Cars Ltd | Wholesale & retail | 2001 |
| Northway Properties Limited | Financial services | 1985 |
| Norvins Accountancy Services Ltd | Professional & scientific | 2000 |
| Nosha Investments Limited | Real estate | 2004 |
| NOT Thought Through Productions Limited | Information & communication | 1995 |
| Novrad Limited | Households | 1998 |
| Nowa Design UK Limited | Professional & scientific | 2009 |
| NRH Consulting Ltd | Professional & scientific | 2005 |
| Ntertainers Limited | Arts & recreation | 2006 |
| Number 19 Consulting Limited | Information & communication | 2002 |
| Numericon Limited | Professional & scientific | 2003 |
| Nunnery Stables (Management Company) Limited | Water & waste | 1982 |
| Nupero Ltd | Professional & scientific | 2019 |
| Nursery Rhymes (H.I.) Limited | Education | 2007 |
| NXC Limited | Administrative & support | 2013 |
| O & S Manufacturing Limited | Manufacturing | 2004 |
| Oak Property Management Limited | Administrative & support | 2000 |
| Oaken Realities Ltd | Financial services | 2012 |
| Oakes Renovations Limited | Construction | 1999 |
| Oakhill Court Residents Management Company Limited | Households | 1996 |
| Oaklake Developments Limited | Real estate | 2004 |
| Oakleigh Court Block 'a' RTM Co. Limited | Real estate | 2004 |
| Oakleigh Park Laundry Company Limited(The) | Other services | 1900 |
| Oakmaster Consulting Ltd | Information & communication | 2000 |
| Oakmont Estates Ltd | Real estate | 2008 |
| Oakway Trading Limited | Wholesale & retail | 1993 |
| Ocean Construction Limited | Construction | 1997 |
| Ocra Ware Limited | Professional & scientific | 2003 |
| Odohertyj Ltd | Real estate | 2023 |
| Ogard Corporate Trusteeship Limited | Financial services | 2021 |
| OH WOW Ltd | Real estate | 2025 |
| OHM Healthcare Limited | Health & social care | 2004 |
| OIG Limited | Information & communication | 1994 |
| Olympic Marketing Limited | Arts & recreation | 2003 |
| OM Soft Solutions Limited | Information & communication | 2012 |
| Omnagen Limited | Manufacturing | 2002 |
| On-Site Catering Services Ltd | Hospitality | 2023 |
| On-Site Catering Services Ltd 2 Ltd | Hospitality | 2024 |
| One Life Later Limited | Information & communication | 2002 |
| Onix Systems Ltd | Construction | 1996 |
| OPC Assessment Limited | Information & communication | 2000 |
| Opcoda Ltd. | Professional & scientific | 1998 |
| OPD Group Holdings Limited | Financial services | 2023 |
| Open Door - ST Albans | Hospitality | 1993 |
| Open Spaces and Bridges Advisory Ltd | Professional & scientific | 2025 |
| Opensale Limited | Professional & scientific | 2002 |
| Optimised Networks Ltd | Information & communication | 2003 |
| Orbital Consulting Limited | Professional & scientific | 1985 |
| Orchard Road Limited | Real estate | 1999 |