| Ntec Support Services Limited | Professional & scientific | 2013 |
| NTK Trade Windows Limited | Construction | 2025 |
| Ntna Limited | Other services | 2025 |
| Nudo Skin Limited | Other services | 2024 |
| NUE Innovations Edmonton Ltd | Wholesale & retail | 2021 |
| NUE Innovations Limited | Wholesale & retail | 2017 |
| Nueducation Ltd | Education | 2023 |
| Nuel Masters Consulting Ltd | Professional & scientific | 2025 |
| Nuella Care Services Ltd | Health & social care | 2022 |
| Nuleaf Homes Limited | Real estate | 2018 |
| Numnut Limited | Other services | 2009 |
| NUR Construction Ltd | Construction | 2026 |
| NUR Valeting Ltd | Wholesale & retail | 2025 |
| Nurah Ltd | Administrative & support | 2016 |
| Nuromist Ltd | Wholesale & retail | 2025 |
| Nurturing Futures, Consultancy Ltd | Information & communication | 2025 |
| Nutaj Limited | Construction | 2016 |
| Nutriafrica Ltd | Hospitality | 2025 |
| Nutriibox Ltd | Manufacturing | 2020 |
| Nutrition Rocks Limited | Extraterritorial | 2021 |
| Nuvella Estates Limited | Real estate | 2016 |
| Nuviz Ltd | Information & communication | 2025 |
| Nuvla Motors Limited | Wholesale & retail | 2025 |
| NV Building Ltd | Construction | 2018 |
| NVL Properties Ltd | Real estate | 2018 |
| NW London Inventories Ltd | Administrative & support | 2016 |
| Nwanya Studio Limited | Professional & scientific | 2024 |
| NWB London Ltd | Construction | 2026 |
| Nyko Structure LP | | 2017 |
| Nyro Ltd | Households | 2018 |
| Nysaessentials Ltd | Wholesale & retail | 2025 |
| Nytex Ltd | Wholesale & retail | 2022 |
| Nöud London Limited | Manufacturing | 2025 |
| N’Dao Limited | Other services | 2022 |
| O & I Consultancy & Coaching Ltd | Professional & scientific | 2025 |
| O I Properties Limited | Real estate | 2020 |
| O&O Global Ltd | Financial services | 2019 |
| O'Donovan Brothers Investments Ltd | Real estate | 2025 |
| O'Donovan Brothers Ltd | Water & waste | 2020 |
| O'Donovan Demolition Limited | Construction | 2014 |
| O'Donovan Holdings Ltd | Financial services | 2018 |
| O'Donovan Property Group Limited | Financial services | 2021 |
| O'Donovan Property Limited | Real estate | 2021 |
| O'Donovan Skip Hire Limited | Water & waste | 2025 |
| O'Donovan Waste Management Limited | Extraterritorial | 1999 |
| O'Reilly,Civils&Earthworks Ltd | Construction | 2025 |
| O. T. (Smoked Salmon) Limited | Manufacturing | 1985 |
| O.K FAM Estates Ltd | Real estate | 2022 |
| O.Z MOT Center Limited | Wholesale & retail | 2026 |
| O2 Catering Limited | Wholesale & retail | 2016 |
| OA Design Studio Ltd | Manufacturing | 2021 |
| OA Latam Advisory Ltd | Professional & scientific | 2020 |
| Oak Care Home Limited | Public administration | 2021 |
| Oak Care Home Support C.I.C. | Health & social care | 2024 |
| Oak Property Invest Ltd | Real estate | 2018 |
| Oak Rose Holdings Ltd | Financial services | 2025 |
| Oakland Building Developments Limited | Real estate | 1998 |
| Oakland Building Services Ltd. | Construction | 1996 |
| Oakland Flooring Limited | Wholesale & retail | 2006 |
| Oakray Electrical, Fire & Security Ltd | Construction | 2023 |
| Oakray Heating and Mechanical Services Ltd | Construction | 2023 |
| Oakray Limited | Construction | 1979 |
| Oakray Property Regeneration Ltd | Construction | 2023 |
| Oakray Renewables Limited | Construction | 2023 |
| Oaks Shipping Limited | Transport & logistics | 2002 |
| OATH707 Ltd | Wholesale & retail | 2023 |
| OB Scaffolding Services Ltd | Construction | 2025 |
| OBA Catering Supplier Limited | Wholesale & retail | 2011 |
| OBA IP Limited | Administrative & support | 2024 |
| OBA Real Estate Ltd | Real estate | 2023 |
| OBA Recruitment UK Ltd | Education | 2019 |
| Obaa the Brand Ltd | Wholesale & retail | 2026 |
| Obbj Ltd | Construction | 2026 |
| Obcie Additions Ltd | Real estate | 2021 |
| Obella Ltd | Wholesale & retail | 2024 |
| OBG International Ltd | Real estate | 2020 |
| Obitre-Gama Ltd | Health & social care | 2021 |
| Obuks Ltd | Professional & scientific | 2020 |
| OC Trading Ltd | Administrative & support | 2026 |
| Ocak IT Solutions Ltd | Information & communication | 2020 |
| Ocbook Community Interest Company | Professional & scientific | 2024 |
| Ocean Floor Creations Ltd | Wholesale & retail | 2023 |
| Ocean South Ltd | Real estate | 2025 |
| Ocean's Ventilation Cleaning Service Ltd | Administrative & support | 2024 |
| Oceanair International Movers Limited | Transport & logistics | 2009 |
| Oceans Media Ltd | Professional & scientific | 2025 |
| Oceans Pathway Care Ltd | Health & social care | 2026 |
| Ocelot Productions Limited | Information & communication | 1985 |
| Ochi Rios Jerk Burgers Ltd | Extraterritorial | 2025 |
| OCS Roofing Ltd | Construction | 2023 |
| Octmerit Ltd | Wholesale & retail | 2026 |
| Octo Rent Ltd | Information & communication | 2025 |
| OD PR Limited | Information & communication | 2017 |
| OD Restoration Ltd | Construction | 2019 |
| ODA Group Limited | Construction | 2019 |
| ODA Life Textile and Furniture Limited | Wholesale & retail | 2017 |
| ODD Wall Limited | Wholesale & retail | 2025 |
| Oddchild Music Limited | Information & communication | 2010 |
| Oddity Ltd | Information & communication | 2015 |
| Oddity Media Ltd | Professional & scientific | 2023 |