| Newfangelt Limited | Professional & scientific | 2013 |
| Newton Launch Systems Ltd | Professional & scientific | 2011 |
| Newton-Faraday Ltd | Construction | 2026 |
| Newvisionz Limited | Professional & scientific | 2005 |
| NEXA4 Solutions Ltd | Information & communication | 2024 |
| Nexcore Solutions Ltd | Information & communication | 2026 |
| Nextgen Sports & Finance Ltd | Professional & scientific | 2024 |
| NG Hamlin UK Limited | Information & communication | 2021 |
| NG Property Ltd | Real estate | 2016 |
| NGC NS LLP | | 2017 |
| Ngsth LLP | | 2017 |
| Nibthwaite Road Freeholders Limited | Real estate | 2015 |
| Nicholas James Property Ltd | Real estate | 2023 |
| Nick Joscelyne SFX Limited | Information & communication | 2015 |
| Nigel Black Limited | Arts & recreation | 2002 |
| Nightingale Court (Rickmansworth) Limited | Households | 1999 |
| Nikaza - Asian Couture Limited | Wholesale & retail | 2016 |
| Nikcas Limited | Administrative & support | 2010 |
| Nimit's EYE Care Limited | Wholesale & retail | 2024 |
| Niramay Path Limited | Health & social care | 2020 |
| Niyot Ltd | Professional & scientific | 2012 |
| Niza ELM Ltd | Wholesale & retail | 2020 |
| Nk.Brothers Groundwork Ltd | Construction | 2026 |
| NL Digital Services Ltd | Administrative & support | 2021 |
| NMA Chauffeur Services Limited | Transport & logistics | 2025 |
| NMD Consultancy Limited | Professional & scientific | 2024 |
| NNH Developments Limited | Construction | 2015 |
| NNH Properties Limited | Construction | 2009 |
| NO.1 Superhighway Limited | Professional & scientific | 1999 |
| Noades Architects Limited | Professional & scientific | 2016 |
| Noah Logistics Limited | Wholesale & retail | 2025 |
| Noble and Nook Limited | Wholesale & retail | 2023 |
| Noble House Consulting Ltd | Professional & scientific | 2017 |
| Noiascape Limited | Construction | 2006 |
| NON Conventional Power Devices Limited | Manufacturing | 2020 |
| Nonno's Express Pizza Ltd | Professional & scientific | 2018 |
| Noor Hardware Limited | Wholesale & retail | 2016 |
| Nordic DRY (UK) Limited | Other services | 2014 |
| Norgent Limited | Information & communication | 2009 |
| Norman Walshe Conceptual Design Ltd | Arts & recreation | 2014 |
| North 88 Meat Produce Company Ltd | Wholesale & retail | 2018 |
| North Country Property Specialists Limited | Real estate | 2017 |
| North Star Transformation Ltd | Information & communication | 2025 |
| Northfields Property Limited | Construction | 2015 |
| Northolt Day Nursery Ltd | Education | 2025 |
| Northside Studios Ltd | Professional & scientific | 2025 |
| Northwood Windows & Doors Ltd | Construction | 2021 |
| Norvell Jefferson Ltd | Professional & scientific | 2013 |
| Notate Ltd | Information & communication | 2025 |
| Notorious Creative Ltd | Professional & scientific | 2021 |
| Nova Solar Group Ltd | Construction | 2025 |
| NP Private Limited | Administrative & support | 2023 |
| Npdc Engineering Ltd | Professional & scientific | 2026 |
| Npec Engineering Services Ltd | Professional & scientific | 2024 |
| NSJ Property Holdings Limited | Real estate | 2022 |
| NT Lifesci Limited | Health & social care | 2026 |
| Ntssuk Limited | Information & communication | 2015 |
| NTT Holdings Limited | Real estate | 2017 |
| NU Investments Limited | Real estate | 2020 |
| Nucleus Industries Limited | Professional & scientific | 2021 |
| Numada Health Care Limited | Health & social care | 2002 |
| Numada Home Care Limited | Administrative & support | 2013 |
| Numada Properties Limited | Real estate | 2022 |
| Number One Bruton Hospitality Limited | Hospitality | 2020 |
| Number One Bruton LLP | | 2018 |
| Nurseempower Limited | Education | 2024 |
| Nussbaumer TV Ltd | Information & communication | 2016 |
| Ny&Sons Ltd | Real estate | 2024 |
| O'Brien Management Services Limited | Professional & scientific | 2016 |
| O'Denthal Limited | Health & social care | 2012 |
| O'Halloran & SON Formwork Limited | Construction | 2017 |
| O'Shea Investments Limited | Construction | 2016 |
| O. Thomas Limited | Administrative & support | 2005 |
| Oak Developers Limited | Real estate | 2024 |
| Oak View Residents Association (Sarratt) Limited | Households | 1995 |
| Oakhill Residents Association Limited | Real estate | 1986 |
| Oaklands Accountancy Ltd | Professional & scientific | 2019 |
| Oaknet Security Ltd | Extraterritorial | 2024 |
| Oakside Alpha Surety Limited | Financial services | 2023 |
| Oaktree Consultants Ltd | Professional & scientific | 2023 |
| Oakvue Ltd | Real estate | 2023 |
| OB 33 Limited | Financial services | 2015 |
| OB Rigging Services Limited | Information & communication | 2017 |
| Ocob & Co Limited | Professional & scientific | 2025 |
| Octagonal Solutions Limited | Professional & scientific | 2018 |
| Octant Marine Limited | Transport & logistics | 2018 |
| Odditychild Limited | Real estate | 2014 |
| Odonnell Haulage & Crane Hire Limited | Transport & logistics | 2015 |
| Offitek Ltd | Manufacturing | 2018 |
| Oggit Ltd | Information & communication | 2017 |
| Okley Mills Enterprises Ltd | Education | 2025 |
| Old Cromwell Road Limited | Real estate | 2026 |
| Old Mill Associates Limited | Real estate | 1997 |
| Oliver Bowes EYE Surgery Limited | Health & social care | 2019 |
| Olives Consulting Services Ltd | Hospitality | 2024 |
| Olka Breeze (UK) Limited | Construction | 1999 |
| Olka Property Ltd | Real estate | 2026 |
| OLS EOT Ltd | Professional & scientific | 2024 |
| Olsofs Property Ltd | Real estate | 2025 |
| Olympus M. Real Estate Limited | Real estate | 2021 |