| NK IT Solutions Limited | Information & communication | 2008 |
| NKP Investments Limited | Financial services | 2006 |
| Nkwe Ltd | Real estate | 2019 |
| Nlca KT22 7PX Ltd | Hospitality | 2016 |
| NO Ordinary House Limited | Professional & scientific | 2025 |
| Nobleman Trading Ltd | Other services | 2024 |
| Nomathemba Ltd | Arts & recreation | 2025 |
| Nontox Ltd | Wholesale & retail | 2026 |
| Norbury Mews Management Ltd | Households | 2025 |
| Norcs LLP | | 2022 |
| Norlev Group Ltd | Construction | 2025 |
| Normford Limited | Households | 1982 |
| Norsewood Arboricultre Ltd | Agriculture & fishing | 2026 |
| North Wales Crusaders Limited | Arts & recreation | 2015 |
| Norton Carpentry & Construction Ltd | Manufacturing | 2022 |
| Nostrapharma Limited | Professional & scientific | 2016 |
| Notemega Limited | Professional & scientific | 1998 |
| Notnotcow Limited | Professional & scientific | 2017 |
| Nourish.Growcookenjoy Ltd | Manufacturing | 2015 |
| Nova Equine Vets Limited | Professional & scientific | 2003 |
| Novalie Ltd | Professional & scientific | 2023 |
| Novel Thinking Ltd | Information & communication | 2025 |
| Novoview Limited | Real estate | 2013 |
| Nowhere in Particular Ltd | Professional & scientific | 2020 |
| Nrbp Limited | Transport & logistics | 2020 |
| NSI (HQ) Limited | Wholesale & retail | 2005 |
| Ntcmed Ltd | Health & social care | 2014 |
| Nucleus Global Solutions Ltd | Administrative & support | 2017 |
| Nudge Energy Limited | Information & communication | 2016 |
| Number 8 Chatsworth Residents Association Limited | Households | 1982 |
| Numbrs Ltd | Professional & scientific | 2019 |
| Numerico Accountants Limited | Professional & scientific | 2019 |
| Nutfield Holdings Trustees Limited | Administrative & support | 2018 |
| Nuthatch Gardens Ltd | Real estate | 2025 |
| Nutley Dean Development Limited | Construction | 2021 |
| Nuway Site Management Limited | Construction | 2018 |
| NYNE9 Limited | Wholesale & retail | 2025 |
| O'Brien Ductwork Services Limited | Energy | 2011 |
| O'Brien Multiservices Ltd | Construction | 2016 |
| O'Connor Advisory Services Limited | Professional & scientific | 2022 |
| O'Connor Software Ltd | Information & communication | 2020 |
| Oak Agility Limited | Information & communication | 2016 |
| Oakfield Catering Ltd | Hospitality | 2024 |
| Oakhampstead Limited | Households | 2019 |
| Oakhill Productions Ltd | Professional & scientific | 2021 |
| Oakleigh Garden Farm & Woodland Management Ltd | Agriculture & fishing | 2011 |
| Oakridge Partners Limited | Construction | 2014 |
| Oakwood Developments LD Limited | Real estate | 2017 |
| Ocean & Sky Ltd | Professional & scientific | 2016 |
| Ocean Villas Management Company Limited | Households | 2024 |
| Oceanwood Trading Limited | Wholesale & retail | 2025 |
| OCS Holdings Limited | Financial services | 2018 |
| Octica Advisory Ltd | Professional & scientific | 2024 |
| Oculus Solutions Limited | Professional & scientific | 2010 |
| Odokai Ltd | Information & communication | 2024 |
| Offthegrid Events Ltd | Administrative & support | 2025 |
| OGG Emea Ltd | Information & communication | 2020 |
| OH Creative Solutions Limited | Information & communication | 2025 |
| Ohsobrow Ltd | Other services | 2020 |
| OK 2 Limited | Professional & scientific | 1998 |
| Old Bakehouse Management Company Limited | Real estate | 2013 |
| Old Blighty Drinks Limited | Wholesale & retail | 2022 |
| Old Oakdene Tannery Limited | Real estate | 2010 |
| Oldham Beach Associates Limited | Professional & scientific | 2013 |
| Oliver Middleton Fencing Ltd | Construction | 2022 |
| Olivia Devereux Interior Design Ltd | Professional & scientific | 2025 |
| Omaswa Consulting Ltd | Professional & scientific | 2018 |
| Omega 741 Ltd | Financial services | 2018 |
| Omili Ltd. | Information & communication | 2016 |
| Omnitransit Solutions Ltd | Transport & logistics | 2026 |
| Omsr Limited | Financial services | 2014 |
| ON My Way Studios Ltd | Information & communication | 2023 |
| ON Point Associates Limited | Public administration | 2019 |
| ON the Hoof Bar and Kitchen Limited | Hospitality | 2017 |
| Onal Albay UK Limited | Real estate | 2019 |
| Once Upon a Time Holdings Limited | Hospitality | 2020 |
| Once Upon a Time Worldwide Limited | Hospitality | 2024 |
| Oncologytree Ltd | Health & social care | 2022 |
| One Financial Solutions Limited | Financial services | 2012 |
| One Focus Consulting Ltd | Professional & scientific | 2019 |
| One Moon Ltd | Hospitality | 2018 |
| One Stop Window Shop Ltd | Construction | 2025 |
| One to TEN Limited | Information & communication | 2004 |
| Onum Ltd | Financial services | 2018 |
| Open Box Consulting Limited | Professional & scientific | 2007 |
| Open Golfer Limited | Wholesale & retail | 2025 |
| OPS Club Ltd | Hospitality | 2019 |
| Opstream Technology Limited | Information & communication | 2019 |
| Optimise 4 Neuro Rehab Ltd | Extraterritorial | 2022 |
| Option Click Design Ltd | Professional & scientific | 2018 |
| Opus Business Systems Limited | Other services | 1992 |
| Opus Digital Solutions Limited | Administrative & support | 2005 |
| Opus Holdings Group Limited | Financial services | 2019 |
| Opus Network Services Limited | Information & communication | 1999 |
| Opus Risk Management Services Limited | Financial services | 2019 |
| Opus Tech Limited | Information & communication | 2020 |
| Opus Technology Ltd | Administrative & support | 2015 |
| Opus Underwriting Limited | Financial services | 2014 |
| ORA DBA Ltd | Information & communication | 2019 |
| Orama Advisory Ltd | Professional & scientific | 2016 |