| Nimrod Close (Northolt) Management Company Limited | Real estate | 1983 |
| Nimyx Limited | Professional & scientific | 2008 |
| Niraj Jewellers Limited | Wholesale & retail | 2004 |
| Nirmalite Limited | Wholesale & retail | 2001 |
| Nirro Limited | Wholesale & retail | 2000 |
| Nirvasha Productions Limited | Arts & recreation | 2006 |
| Nirvasit Ltd | Information & communication | 2023 |
| Nish Consulting Limited | Professional & scientific | 2004 |
| Nitram Vacuum Heat Treatments Company Limited | Professional & scientific | 1939 |
| NJB Consulting Ltd | Information & communication | 1998 |
| NK Consulting (UK) Limited | Extraterritorial | 2002 |
| Nkpd Limited | Real estate | 2020 |
| NM Frontier UK Ltd | Wholesale & retail | 2024 |
| NNR Global Logistics UK Limited | Transport & logistics | 1991 |
| Noble Traders Limited | Financial services | 2004 |
| Nodit Limited | | 1895 |
| Noel Glennon Limited | Arts & recreation | 2015 |
| Noel Pach Limited | Administrative & support | 2004 |
| Noor Shipping (U.K.) Company Limited | Transport & logistics | 2002 |
| Norcil Ltd | Real estate | 1955 |
| Norris Engineering (Hobs & Cutters) Limited | Manufacturing | 1941 |
| North Mymms Electronics Limited | | 1978 |
| North Star Garage Limited | Wholesale & retail | 1993 |
| Northern Holdings Company Limited | Professional & scientific | 1983 |
| Northolt Guest House Limited | Wholesale & retail | 2001 |
| Northwood Trading Centre Limited | Energy | 1997 |
| Norton Bridges & Co. Limited | Professional & scientific | 1997 |
| Norvic Building Contractors Limited | Wholesale & retail | 1990 |
| Noshers of Pinner Green Limited | Wholesale & retail | 2005 |
| Nouveau Consultants (2004) Limited | Professional & scientific | 2004 |
| Nova Atlas (UK) Limited | Wholesale & retail | 1995 |
| Nova Fresh Ltd | Wholesale & retail | 2024 |
| NRK Properties Limited | Real estate | 2004 |
| Nteractive Group Limited | Financial services | 2018 |
| Ntpt Holdings Limited | Wholesale & retail | 2024 |
| NTS Graphics Limited | Information & communication | 1998 |
| Nuland Building Limited | Construction | 2006 |
| Number Crunchers Limited | Professional & scientific | 2003 |
| Numbers 62/64/66/68 Lyndhurst Gardens (Enfield) Management Co. Limited | Extraterritorial | 2000 |
| Numbers by Design Limited | Professional & scientific | 1977 |
| NUR Limited | Real estate | 1997 |
| Nutrivana Ltd | Wholesale & retail | 2025 |
| Nuvmarcs Limited | Wholesale & retail | 2013 |
| NVM IT Consultancy Limited | Information & communication | 2003 |
| NW Lettings Ltd | Real estate | 2021 |
| O'Connell Plant and Groundworks Limited | Construction | 1989 |
| O'Dareo Limited | Administrative & support | 2011 |
| O'Hara Bros. Surfacing Limited | Construction | 1975 |
| O'Neills Developments Limited | Construction | 2008 |
| O'Rorke Works Limited | Arts & recreation | 2013 |
| O.J.K Consulting Limited | Professional & scientific | 2002 |
| Oak Heights School Ltd | Education | 2006 |
| Oakbridge Development & Construction Company Limited | Construction | 1964 |
| Oakdene Partners Limited | Information & communication | 2006 |
| Oake & Company (General Merchants) Limited | Wholesale & retail | 1954 |
| Oaklands Digital Ltd | Information & communication | 2017 |
| Oakshott Productions Limited | Information & communication | 2001 |
| Oakside Consultants Limited | Professional & scientific | 1996 |
| Oaktree Garden Products Limited | Manufacturing | 1987 |
| Oakwood Advisors Limited | Professional & scientific | 2007 |
| Oasis Limited | Information & communication | 1998 |
| Oberoi Enterprises (UK) Limited | Construction | 2007 |
| Obopt Ltd | Information & communication | 2020 |
| Obsidian Environmental Services Ltd | Administrative & support | 2024 |
| OC318810 LLP | | 2006 |
| Oceana Investments Ltd | Real estate | 2023 |
| Odessey Limited | Wholesale & retail | 1986 |
| Odin Consultants Limited | Professional & scientific | 2006 |
| Odina Consulting Services Limited | Professional & scientific | 2003 |
| Odu-Tech and Health Care Services Limited | Health & social care | 2015 |
| Odyssey Developments (UK) Limited | Construction | 2007 |
| OHM Electronics Limited | Other services | 1987 |
| Oiticij Pure Limited | Wholesale & retail | 2002 |
| Okus Properties Limited | Real estate | 2002 |
| Olab Ltd | Other services | 2002 |
| Old Nursery Place RES. Assoc. (Ashford) Limited | Households | 1993 |
| Old Skool Enterprises Limited | Construction | 2002 |
| Olson Electronics Ltd | Manufacturing | 1961 |
| Olsthorne Limited | Real estate | 1981 |
| Olympic Plant Hire Limited | Construction | 1980 |
| Omega 5 (UK) Limited | Administrative & support | 1988 |
| Omega Intelligent Solutions Limited | Education | 2004 |
| Omega Platinum Limited | Construction | 2017 |
| Omega Spare Parts Limited | Wholesale & retail | 2010 |
| Omnia Assets Limited | Extraterritorial | 2017 |
| Omnia Developments Ltd | Extraterritorial | 2017 |
| Omnia Homes Ltd | Extraterritorial | 2017 |
| Omnia Housing Ltd | Real estate | 2002 |
| Omnia Investments Limited | Extraterritorial | 2017 |
| Omnia Properties Limited | Extraterritorial | 2017 |
| Omnia RCF Ltd | Real estate | 2026 |
| Omwood Limited | Hospitality | 1987 |
| ON a Roll (UK) Ltd | Transport & logistics | 2004 |
| ON the Rails Limited | Wholesale & retail | 1999 |
| Oncore Developments Ltd | Real estate | 2004 |
| One Bank Ltd | Financial services | 2005 |
| One Enterprise Limited | Professional & scientific | 2006 |
| One More Music Company Ltd | Arts & recreation | 2006 |
| One People Limited | Information & communication | 2001 |
| One Sight Residentials Limited | Real estate | 2019 |