| NO53 Park Road Limited | Real estate | 2023 |
| Noble Premium Limited | Wholesale & retail | 2021 |
| Noctra Team Ltd | Professional & scientific | 2025 |
| Nolan Group Limited | Construction | 2020 |
| Nomi Digital Limited | Information & communication | 2016 |
| Nookz & Cranniez Ltd | Administrative & support | 2022 |
| Norfolk Rivers Consortium Limited | Construction | 2022 |
| Norlington Road Developments Limited | Construction | 2016 |
| Norman Hart (Marquee Hire) Limited | | 1982 |
| Normanhurst School Ltd | Education | 2015 |
| North Camp Properties Limited | Real estate | 2019 |
| North London Consultants Ltd | Health & social care | 2012 |
| North London Pizza Holdings Limited | Financial services | 2023 |
| North Weald Heritage Aviation Ltd | Manufacturing | 2016 |
| Northern Secure Limited | Administrative & support | 2025 |
| Northway House Limited | Real estate | 1960 |
| Northwood (Southend) Limited | Real estate | 2005 |
| Norton Close Management Limited | Households | 1999 |
| Noubody Ltd | Wholesale & retail | 2023 |
| Nova Bricks Ltd | Construction | 2025 |
| Nova Construction Group Ltd | Construction | 2026 |
| Nova Taste Ltd | Hospitality | 2025 |
| Novagrade Limited | Real estate | 2000 |
| Novastar Trading Limited | Construction | 1999 |
| Noveltek UK Limited | Other services | 2018 |
| Novelty Products Limited | Extraterritorial | 2011 |
| Novoto by Kate Ltd | Hospitality | 2025 |
| NPG Estates Ltd | Real estate | 2014 |
| NRA Construction Limited | Construction | 2014 |
| NRG Services Ltd | Construction | 2015 |
| NRV Accountants Ltd | Professional & scientific | 2016 |
| NRV Tax Ltd | Professional & scientific | 2010 |
| NS Elite Carpentry & Joinery Limited | Manufacturing | 2025 |
| NS London Ltd | Mining & quarrying | 2017 |
| NS Properties London Ltd | Real estate | 2020 |
| NS Property Trading Limited | Construction | 2021 |
| NS UK Residential Ltd | Real estate | 2019 |
| Nsnatched London Ltd | Wholesale & retail | 2025 |
| Nssk Limited | Real estate | 2018 |
| NU ERA Contractors Ltd | Construction | 2011 |
| Nuba Limited | Transport & logistics | 2021 |
| Nuevo International BIO Security UK Limited | Wholesale & retail | 2021 |
| Nuevopacks Limited | Wholesale & retail | 2025 |
| Number Forty Limited | Real estate | 2019 |
| Number Two Devonshire Gardens (Management) Limited | Real estate | 1975 |
| Numeni Limited | Information & communication | 2018 |
| Numuw Co Ltd | Administrative & support | 2026 |
| Nuove Cucine Ltd | Construction | 2018 |
| Nushaf Limited | Wholesale & retail | 2025 |
| NVK Drylining Ltd | Construction | 2013 |
| Nxtz Limited | Real estate | 2023 |
| Nylon Retail Ltd. | Wholesale & retail | 2018 |
| Nylor Limited | Construction | 2018 |
| Nylospray Limited | Manufacturing | 1968 |
| O Soupa MAN Limited | Hospitality | 2025 |
| O'Reilly Promotions Ltd | Professional & scientific | 2016 |
| O.C. Tanner Limited | Administrative & support | 2001 |
| Oak Enterprises Limited | Wholesale & retail | 2014 |
| Oak Farm Projects Ltd | Construction | 2021 |
| Oak Fields (Lawshall) Management Company Limited | Households | 2025 |
| Oak Tree Schools Holdings Limited | Administrative & support | 1995 |
| Oakdale Court Limited | Households | 1995 |
| Oakfield Broking Limited | Extraterritorial | 2011 |
| Oaklands (Warren Hill) Limited | Real estate | 2013 |
| Oaklands School Limited | Education | 1998 |
| Oakmount & Partners Limited | Real estate | 2009 |
| Oakmount Global Management Limited | Financial services | 2011 |
| Oakmount Holdings Management Limited | Financial services | 2026 |
| Oakmount Private Holdings Limited | Real estate | 2013 |
| Oaks Care Limited | Health & social care | 2004 |
| Oakwood Contracts (London) Ltd | Construction | 2018 |
| Oakwood Corporation Limited | Wholesale & retail | 1998 |
| Oakwood Court Limited | Real estate | 1988 |
| Oakwood Food & Wines Ltd | Wholesale & retail | 2002 |
| Oakwood Hill Investment Ltd | Real estate | 2023 |
| OBC Group Limited | Construction | 2020 |
| Obros Investments Limited | Extraterritorial | 2005 |
| Ocean Villas Limited | Hospitality | 2001 |
| OCH Envoy Limited | Administrative & support | 2017 |
| Octaryn Systems Ltd | Manufacturing | 2026 |
| ODD Publishing Media House Ltd | Information & communication | 2025 |
| Oddy Building Services Limited | Construction | 2007 |
| Odhav Puri Ltd | Administrative & support | 2023 |
| Oelofse Dentserv Limited | Health & social care | 2013 |
| OG Holdingz Ltd | Financial services | 2024 |
| OGC Enforcement Limited | Administrative & support | 2025 |
| OGI Builders Limited | Construction | 2013 |
| Ogilvie Fire Protection Ltd | Construction | 2016 |
| Ohholdco Limited | Construction | 2026 |
| OJN Consultancy Limited | Professional & scientific | 2026 |
| Olamam Property Investment Limited | Real estate | 2025 |
| Old Oak London Management Company Limited | Households | 2025 |
| Old Post House (Woodford Green) Limited | Households | 2020 |
| OLE Academy Limited | Education | 2024 |
| Oli&Ben Ltd | Wholesale & retail | 2017 |
| Olinski Plumbing and Heating Limited | Construction | 2016 |
| Olive & Stone Coffee Bistro Ltd | Hospitality | 2026 |
| Olive Builders Ltd | Construction | 2026 |
| Olivié Outside Ltd | Professional & scientific | 2016 |
| OLÉ Futsal Limited | Arts & recreation | 2015 |