| Northern Healthcare MAN Ltd | Health & social care | 2017 |
| Northern Medico Ltd | Health & social care | 2024 |
| Northfield's Beauty Ltd | Other services | 2019 |
| Northstar Rebuild Limited | Wholesale & retail | 2026 |
| Norton Building Services Ltd | Construction | 2018 |
| Nour Cars Ltd | Wholesale & retail | 2018 |
| Nova Build London Ltd | Construction | 2018 |
| Nova Point Trading Company Ltd | Wholesale & retail | 2026 |
| Nova Security Group Ltd | Administrative & support | 2023 |
| Novacare Clinical Ltd | Health & social care | 2026 |
| Novel Bites Limited | Hospitality | 2025 |
| Novel Housing Limited | Real estate | 2021 |
| Novel Restaurants Limited | Hospitality | 2022 |
| NSA Training Ltd | Professional & scientific | 2014 |
| NSC Sterling Limited | Wholesale & retail | 2025 |
| NSN Medtech UK Ltd | Wholesale & retail | 2026 |
| Nsrl Ltd | Real estate | 2021 |
| NTK Consulting Group Limited | Professional & scientific | 2024 |
| NTS 14 Limited | Transport & logistics | 2020 |
| NTS Records Ltd | Information & communication | 2021 |
| Nuch Limited | Arts & recreation | 2016 |
| NUE Interiors Limited | Construction | 2022 |
| NUMEDIC24 Ltd | Health & social care | 2024 |
| Nuriah Limited | Wholesale & retail | 2026 |
| NUS Holds Ltd | Financial services | 2025 |
| NUS Property Investment Ltd | Real estate | 2025 |
| Nush Marlins Developments Limited | Construction | 2018 |
| Nusrat Motors Limited | Wholesale & retail | 2020 |
| Nusrat Trading Ltd | Transport & logistics | 2019 |
| Nutricherry Limited | Information & communication | 2005 |
| NV Bright Ltd | Administrative & support | 2017 |
| NVI2017 Trading Ltd | Transport & logistics | 2017 |
| NVS Holdings Limited | Real estate | 2021 |
| Nwarege Limited | Real estate | 2024 |
| NWG Building Maintenance Ltd | Administrative & support | 2025 |
| NY Builders Ltd | Construction | 2014 |
| Nylers Ltd | Arts & recreation | 2012 |
| O Property Group Ltd | Real estate | 2024 |
| O'Connor Businesslinks Ltd | Real estate | 2008 |
| O'Connor Supplementary Education Ltd | Education | 2025 |
| O'Halloran & O'Brien Limited | Construction | 1972 |
| Oakmead Property Management Limited | Households | 2021 |
| Oakview Holding Real Estate Ltd | Real estate | 2024 |
| Oasis Plus Care Services Ltd | Public administration | 2020 |
| OB Construction & Properties Ltd | Construction | 2016 |
| Obgyn Ltd | Information & communication | 2025 |
| Obgynae Ltd | Information & communication | 2025 |
| Oceancliffe Real Estates Ltd | Real estate | 2025 |
| Octahedron Ltd | Wholesale & retail | 2024 |
| Odugbemi Bluebrickman Studios Limited | Information & communication | 2015 |
| OES Healthcare Limited | Health & social care | 2013 |
| OES Holds Ltd | Financial services | 2021 |
| OES Investments Properties Ltd | Real estate | 2021 |
| Of-A-Visions Limited | Arts & recreation | 2022 |
| Office Isolate Ltd | Wholesale & retail | 2020 |
| Offitec Limited | Manufacturing | 1991 |
| Oggul Limited | Construction | 2022 |
| Ohob Building Contractors Limited | Construction | 2008 |
| Ohob Group Limited | Construction | 2008 |
| Ohob Holdings Limited | Professional & scientific | 2012 |
| OK Traders Ltd | Wholesale & retail | 2025 |
| Okesanya Medicare Limited | Health & social care | 2016 |
| Okiko Ltd | Construction | 2025 |
| Okolossus Ltd | Health & social care | 2025 |
| Old Library Lodge (2018) Ltd | Households | 2018 |
| Old Wolf Ltd | Administrative & support | 2024 |
| OLI & Ayla Properties Ltd | Real estate | 2023 |
| Omega Maintenance Services Limited | Administrative & support | 2014 |
| Omega-Aplus Services Ltd. | Education | 2013 |
| OMJ Networks Limited | Construction | 2021 |
| Omnibot Nexus Ltd | Information & communication | 2024 |
| Omould Technology (UK) Co., Ltd | Wholesale & retail | 2021 |
| ON Point Property Management Ltd | Real estate | 2015 |
| Oncology Holds Ltd | Financial services | 2026 |
| Oncology Investment Property Ltd | Real estate | 2026 |
| Oncology Management Limited | Health & social care | 2015 |
| Oncotechnologies Ltd | Health & social care | 2020 |
| One Take Media Ltd | Information & communication | 2019 |
| One Window Business Solution Ltd | Professional & scientific | 2019 |
| Oneex Lets Ltd | Real estate | 2023 |
| Oneex Ltd | Construction | 2023 |
| Online Corner Shop Limited | Wholesale & retail | 2024 |
| Onlydate.Com Limited | Information & communication | 2002 |
| Onlysnaps Ltd | Professional & scientific | 2023 |
| Onslow Grange Estates Limited | Real estate | 2026 |
| Ontrack Cars Ltd | Transport & logistics | 2023 |
| OOM Shivaya Ltd | Wholesale & retail | 2017 |
| Opaline Ltd | Wholesale & retail | 2025 |
| Open Box Entertainment Ltd | Wholesale & retail | 2023 |
| Open Gate International Ltd | Wholesale & retail | 2026 |
| Opgroup Ltd | Construction | 2025 |
| Oprea Constructions Ltd | Construction | 2019 |
| Optical Surfaces Holdings Limited | Financial services | 2025 |
| Options Services Kent Ltd | Households | 2019 |
| Opulent Creations Limited | Construction | 2023 |
| Orama Vibes Ltd | Information & communication | 2015 |
| Orange Fish Promotional Marketing Ltd | Wholesale & retail | 2025 |
| ORANGE23 Ltd | Information & communication | 2019 |
| Orangecrust Ltd | Wholesale & retail | 2025 |
| Ordinary Global Limited | Wholesale & retail | 2018 |