| Nighthawk Industries Ltd | Other services | 2018 |
| Nighthawk Properties Ltd | Real estate | 2025 |
| Nikki's Driving School Ltd | Education | 2025 |
| Nimsim Ltd | Professional & scientific | 2013 |
| Ninefields Holdings Limited | Administrative & support | 1990 |
| Niriv Investments Ltd | Real estate | 2021 |
| Nisire Limited | Real estate | 2021 |
| NJ Cards UK Ltd | Wholesale & retail | 2023 |
| NJB - Machines, INK & Sevices Ltd | Manufacturing | 2025 |
| NJD Homes Limited | Real estate | 2018 |
| NJG Solutions Ltd | Professional & scientific | 2020 |
| NJJ Limited | Professional & scientific | 2013 |
| Njpg Limited | Construction | 2020 |
| Nnovatei (UK) Limited | Real estate | 2019 |
| Noakes Property Investment Group Ltd | Administrative & support | 2026 |
| Noble Legal Services Limited | Professional & scientific | 2026 |
| Noble Probate Services Limited | Professional & scientific | 2026 |
| Noel Diabetes Training Ltd | Health & social care | 2026 |
| Noel Mcwilliam Ltd | Financial services | 2014 |
| Noomez Project Management Ltd | Administrative & support | 2025 |
| Nora Turjanski Ltd | Administrative & support | 2019 |
| Normalfactor Limited | Administrative & support | 1998 |
| Normalu UK Limited | Professional & scientific | 2011 |
| North Weald Flying Group Limited | Administrative & support | 2002 |
| Northern Home Counties Federation of Spiritualist Churches Limited(The) | Other services | 1958 |
| NOT Just Banners Limited | Manufacturing | 2024 |
| Notera Limited | Real estate | 2026 |
| Nova Bureau Ltd | Real estate | 2024 |
| Nova-Cad Ltd | Construction | 2025 |
| NOW Management Solutions Ltd | Information & communication | 2024 |
| NP Houses Ltd | Real estate | 2024 |
| NPC Properties Limited | Real estate | 2022 |
| NPT Software Ltd | Information & communication | 2022 |
| NS & Son's Construction Ltd | Construction | 2019 |
| Nuna Studio Ltd | Professional & scientific | 2024 |
| Nupath Care Services Ltd | Health & social care | 2022 |
| Nupath Recruitment Agency Ltd | Health & social care | 2020 |
| Nutel Holdings Limited | Financial services | 2021 |
| Nykchazza Ltd | Information & communication | 2024 |
| O Millers Electrical Services Ltd | Construction | 2026 |
| O.I.W. (Steels) Limited | Manufacturing | 1979 |
| Oakdown Limited | Administrative & support | 1981 |
| Oakfield Programme Innovations Ltd | Professional & scientific | 2025 |
| Oakhall Ltd | Professional & scientific | 2024 |
| Oaklands Services Limited | Other services | 2019 |
| Oaklea Business Consultancy Ltd | Administrative & support | 2024 |
| Oaklea Holdings Ltd | Real estate | 2023 |
| Oakstone Property Holdings Ltd | Real estate | 2026 |
| Oakview Stone Ltd | Administrative & support | 2010 |
| Oakwood Developments Ltd | Administrative & support | 2014 |
| Oakwood Podiatry Ltd | Extraterritorial | 2021 |
| OAT Properties Limited | Real estate | 2017 |
| OBC Services Ltd | Professional & scientific | 2026 |
| OBR Electrical Limited | Construction | 2026 |
| OCDNADLEIF42 Ltd | Professional & scientific | 2013 |
| Ocean Asset Management Ltd | Real estate | 2016 |
| Ocean Bond Services Limited | Construction | 2018 |
| Ocean Contracts Limited | Construction | 2024 |
| Ocean Tech Contractors Limited | Construction | 2001 |
| OCL Rail Limited | Construction | 2007 |
| Octopus Networks Ltd | Information & communication | 2011 |
| Octopus Real Estate Limited | Real estate | 2021 |
| OF1 Plumbing and Heating Limited | Construction | 2025 |
| Office Fruit Daily Ltd | Wholesale & retail | 2025 |
| Office Surplus Limited | Wholesale & retail | 2021 |
| OG Solutions Limited | Extraterritorial | 2019 |
| OGC Visuals Limited | Arts & recreation | 2024 |
| Ogle Technology Ltd | Information & communication | 2020 |
| OGR Electrical Limited | Construction | 2026 |
| OH Crumbs by Chloe Ltd | Manufacturing | 2023 |
| OJN Electrical Ltd | Construction | 2020 |
| Ojohn and SON Limited | Administrative & support | 2024 |
| Ojuwoye Ltd | Wholesale & retail | 2025 |
| OKN Investment Ltd | Real estate | 2025 |
| Oktav Tiling Ltd | Construction | 2019 |
| Old Oak PUB Company Limited | Hospitality | 2026 |
| Olivers on the Beach Limited | Hospitality | 2015 |
| Oloyede Ltd | Wholesale & retail | 2024 |
| Omega Loans Ltd | Financial services | 2017 |
| Omega Refrigeration Services Limited | Manufacturing | 2012 |
| Omni Operatives Limited | Administrative & support | 2026 |
| Omniap Limited | Information & communication | 2017 |
| ON Platform Limited | Information & communication | 2013 |
| One Call Cleans IT ALL Limited | Households | 2018 |
| One Choice Marketing Ltd | Administrative & support | 2008 |
| One Make UP Limited | Other services | 1998 |
| One Photographic Ltd | Professional & scientific | 2001 |
| One Represents Ltd | Administrative & support | 2012 |
| One Stop Car Garage Ltd | Wholesale & retail | 2025 |
| One Stop Cooling & Heating Ltd | Construction | 2022 |
| One Stop Ground Work Ltd | Construction | 2018 |
| One Takeaway Limited | Hospitality | 2023 |
| Oneton Holdings Ltd | Financial services | 2023 |
| Ongar Developments Ltd | Construction | 2014 |
| Onix Capital UK Ltd | Financial services | 2018 |
| Onutra Ltd | Manufacturing | 2026 |
| Open Arms Network CIC | Hospitality | 2025 |
| Operator Licence Services Ltd | Professional & scientific | 2021 |
| Optimal Point Ltd | Wholesale & retail | 2025 |
| Optime Finance Ltd | Professional & scientific | 2022 |