| Normanton Lodge Care Ltd | Health & social care | 2022 |
| North END Avenue Company Limited | Households | 2025 |
| North Reserves Ltd | Financial services | 2026 |
| North Reserves Paddock Ltd | Hospitality | 2026 |
| North-South Travel Limited | Administrative & support | 1981 |
| Northpoint (Residential Holdings) Limited | Extraterritorial | 2017 |
| Northpoint Printing Ltd | Manufacturing | 2009 |
| Northrock Consulting Ltd | Professional & scientific | 2024 |
| Norvad Construction Ltd | Construction | 2023 |
| Nostromo Finance Ltd | Professional & scientific | 2025 |
| Nouanalytics Ltd | Administrative & support | 2025 |
| Novascorpio Limited | Administrative & support | 2013 |
| Novelty Structures Ltd | Wholesale & retail | 2020 |
| November Ltd | Construction | 2025 |
| Novo Cleaning Services Ltd | Administrative & support | 2026 |
| NOX London Ltd | Administrative & support | 2024 |
| Nrgfarm Limited | Information & communication | 2010 |
| NS Herbalist UK Limited | Agriculture & fishing | 2014 |
| NSZ Private Ltd | Transport & logistics | 2023 |
| NT Wholesales Ltd | Wholesale & retail | 2026 |
| Numerx Ltd | Other services | 2020 |
| Nuvate Marketing Limited | Professional & scientific | 2026 |
| NV Cargo Limited | Transport & logistics | 2018 |
| Nyamuzihwa Limited | Health & social care | 2018 |
| NYK Financial Services Ltd | Professional & scientific | 2025 |
| Nyuki Tech Ltd | Information & communication | 2024 |
| O V Facilities Ltd | Administrative & support | 2023 |
| Oak Builders Ltd | Construction | 2019 |
| Oak Cottage Pet Hotel Ltd | Other services | 2024 |
| Oak Place Management Limited | Households | 1993 |
| Obsession Cleaners Ltd | Administrative & support | 2018 |
| Obstetrics & Feto-Maternal Medicine Limited | Extraterritorial | 2010 |
| Ocean Vista Limited | Construction | 2023 |
| Octoberboy Ltd | Wholesale & retail | 2026 |
| Ocura 360 Limited | Information & communication | 2025 |
| Oddment Labs Ltd | Information & communication | 2013 |
| Ogam Ltd | Wholesale & retail | 2019 |
| Ohaio UK Limited | Wholesale & retail | 2021 |
| Ohp&Bi Limited | Hospitality | 2019 |
| OIG Controls Ltd | Construction | 2024 |
| Oishii Grill Ltd | Hospitality | 2024 |
| OJB Investments Ltd | Construction | 2016 |
| OJL UK Ltd | Hospitality | 2023 |
| OK Grace Ltd | Manufacturing | 2022 |
| Okbo & Partners Ltd | Hospitality | 2017 |
| Old Malden Limited | Construction | 2023 |
| Old Malden Partners Limited | Construction | 2023 |
| Olive House Ltd | Hospitality | 2011 |
| Oliver Haynes Personal Training Ltd | Arts & recreation | 2007 |
| Olu-Moyek Ltd | Health & social care | 2012 |
| Omax Projects Ltd | Construction | 2025 |
| Omega Plus Development Ltd | Real estate | 2023 |
| Omega Plus Rental Limited | Real estate | 2024 |
| Omni Local Ltd | Information & communication | 2012 |
| ON Point Recruitment Limited | Administrative & support | 2012 |
| Onassis Apparel UK Limited | Professional & scientific | 2012 |
| Onassis Clothing UK Limited | Professional & scientific | 2012 |
| One Business Consultants Ltd | Professional & scientific | 2019 |
| One Logistics Ltd | Administrative & support | 2012 |
| One OFF Interiors Ltd | Professional & scientific | 2025 |
| Onedon Media Limited | Extraterritorial | 2016 |
| Onidentity Ltd | Information & communication | 2019 |
| Onmt Ltd | Transport & logistics | 2022 |
| Onnik Ltd | Transport & logistics | 2023 |
| Onsb Ltd | Transport & logistics | 2019 |
| Onsiteautos Limited | Wholesale & retail | 2017 |
| Ontarget Pharma Consultancy Limited | Professional & scientific | 2015 |
| Onwic Limited | Wholesale & retail | 2024 |
| Onyou Group Ltd | Other services | 2023 |
| Optimal Construction Group Limited | Real estate | 2021 |
| Orayaa Ltd | Wholesale & retail | 2025 |
| ORB Vision Limited | Construction | 2000 |
| Orbital Business Consultants Ltd | Professional & scientific | 2023 |
| Orchid Property Corporation Ltd | Real estate | 2015 |
| Orchid Property Investments Ltd | Real estate | 2017 |
| Order Creative Ltd | Arts & recreation | 2025 |
| Organic Consultancy Ltd | Professional & scientific | 2016 |
| Oriel Investments (UK) Limited | Construction | 2003 |
| Oriental Star Consulting Limited | Professional & scientific | 2015 |
| Origo Byte Ltd | Information & communication | 2026 |
| ORZ Ltd | Real estate | 2009 |
| Osscar Properties Ltd | Real estate | 2020 |
| Otago Build Ltd | Administrative & support | 2009 |
| OTG Auto Techs Limited | Wholesale & retail | 2025 |
| OTG Group Ltd | Professional & scientific | 2022 |
| OTS Computer Solutions Ltd | Information & communication | 2007 |
| Ottoman Ventures LLP | | 2012 |
| Ouiteo Technologies Ltd | Information & communication | 2021 |
| Oule Ltd | Professional & scientific | 2013 |
| OUQ Holdings Ltd | Wholesale & retail | 2021 |
| Outhost Ltd | Information & communication | 2025 |
| Overseas UK Trading Ltd | Wholesale & retail | 2021 |
| Owairaka Consulting Limited | Information & communication | 2009 |
| Owls Digital Ltd | Information & communication | 2026 |
| Oxbridge Centre (UK) Limited | Education | 2002 |
| Oxford Acacia Tree Ltd | Real estate | 2020 |
| OZ Partners Ltd | Professional & scientific | 2011 |
| P&3J Limited | Other services | 2008 |
| P&J DE Villiers Limited | Arts & recreation | 2018 |
| P&R Accounting UK Ltd | Professional & scientific | 2018 |