| NO Labelling Limited | Wholesale & retail | 2024 |
| NO Monopoly Geniuses Ltd | Arts & recreation | 2020 |
| NO Time to DIE Ltd | Arts & recreation | 2020 |
| NO TV Limited | Information & communication | 2000 |
| Nobility Trading Ltd | Administrative & support | 1997 |
| Noble Discount Store Limited | Wholesale & retail | 2024 |
| Noble Turner Associates Limited | Professional & scientific | 2003 |
| Noblix Ltd | Wholesale & retail | 2026 |
| Nobre Store Ltd | Wholesale & retail | 2026 |
| Noendquest Ltd | Information & communication | 2022 |
| Nomedaskeen Ltd | Professional & scientific | 2025 |
| Noon & Bloom Ltd | Hospitality | 2026 |
| Noor Remit Ltd | Manufacturing | 2020 |
| Nooravita UK Limited | Wholesale & retail | 2023 |
| Nordsten Grinding & SAW Works Limited | Manufacturing | 1975 |
| Norfolk Realty Ltd | Real estate | 2014 |
| Norman and Lewis Limited | Financial services | 1993 |
| Normas Newsagents Limited | Wholesale & retail | 2003 |
| North Hill Exchange Limited | Real estate | 1994 |
| North Point Rental Properties Ltd | Real estate | 2026 |
| North Thames Construction Limited | | 1973 |
| Northbrooke Limited | Real estate | 2006 |
| Northern Design House Limited | Information & communication | 2006 |
| Northern Information Technology Consultancy Limited | Information & communication | 2001 |
| Northern Properties (Braintree) Ltd | Real estate | 2020 |
| Northern Signals Ltd | Other services | 2018 |
| Northman Brookes Ltd | Construction | 2025 |
| Northumberland DRY Relief Lounge Ltd | Wholesale & retail | 2026 |
| Norwich China Town Limited | Extraterritorial | 2022 |
| Norwich Road (Attleborough) Management Company Limited | Households | 2019 |
| Notch Limited | Information & communication | 2003 |
| Nounsley Surveying Limited | Administrative & support | 2003 |
| Nova Realty Ltd | Real estate | 2021 |
| Nova Systems | | 1996 |
| Novahub Techonologies Limited | Wholesale & retail | 2026 |
| Novaia Ltd | Wholesale & retail | 2025 |
| Novaverse Creation Ltd | Wholesale & retail | 2024 |
| Novekai Ltd | Other services | 2025 |
| Novo Health Limited | Administrative & support | 2025 |
| NRG Property Ltd | Real estate | 2024 |
| NS Store Ltd | Wholesale & retail | 2026 |
| NSH Health Limited | Health & social care | 2017 |
| NSO (UK) Limited | Professional & scientific | 2005 |
| NSR Solutions Limited | Professional & scientific | 2007 |
| Nszz Property Limited | Real estate | 2025 |
| Ntweddings Ltd | Information & communication | 2015 |
| Nudge Nudge Limited | Administrative & support | 2004 |
| Nueretz Students Ltd | Real estate | 2023 |
| Nugila Property Ltd | Real estate | 2022 |
| Numz Holdings Ltd | Real estate | 2020 |
| Nunngeo Consulting Limited | Professional & scientific | 2006 |
| Nurture DEN Ltd | Health & social care | 2024 |
| Nutramart Limited | Wholesale & retail | 2024 |
| Nutrivive Health Ltd | Wholesale & retail | 2024 |
| Nuucom Limited | Real estate | 2023 |
| Nuucore Ltd | Construction | 2025 |
| Nwcumbrian Properties Limited | Real estate | 2022 |
| NXT Level Care Ltd | Health & social care | 2025 |
| NY Explorer Ltd | Professional & scientific | 2022 |
| Nzee Professionals Ltd | Other services | 2016 |
| O E Longshaw (Seals) Limited | Wholesale & retail | 2004 |
| O'Carroll Engineering UK Limited | Professional & scientific | 2018 |
| O'Clay Consultancy Limited | Other services | 2015 |
| O-I Glass Limited | Manufacturing | 1953 |
| O.Comitti and SON Limited | Manufacturing | 1897 |
| O.J.M Insulations Limited | Construction | 2001 |
| O3WEB Orange Limited | Information & communication | 2026 |
| Oak Court (South Ockendon) Residents Association Limited | Other services | 1989 |
| Oak Tree Gallery Limited | Wholesale & retail | 2007 |
| Oakdove Limited | Real estate | 1987 |
| Oakhill Property Investments Limited | Real estate | 2017 |
| Oakley Adventures Ltd | Arts & recreation | 2004 |
| Oakley Builders Limited | Wholesale & retail | 1990 |
| Oakridge Global Holdings Limited | Real estate | 2017 |
| Oakway Builders Ltd | Construction | 2026 |
| Oakwood Fencing Services Limited | Manufacturing | 2003 |
| Oakwood Global Ltd | Wholesale & retail | 2026 |
| Oakwood Pharmacy Limited | Wholesale & retail | 1996 |
| Oamg Ltd | Real estate | 2024 |
| Oasis Community Services Limited | Extraterritorial | 1989 |
| Oasis Premium Mart Ltd | Wholesale & retail | 2024 |
| Obelus Clothing Limited | Wholesale & retail | 2019 |
| OBI NWA Medicals Limited | Health & social care | 2026 |
| Obilin Limited | Health & social care | 2025 |
| Oblivarion Digital Ltd | Wholesale & retail | 2025 |
| Obrro Limited | Wholesale & retail | 2023 |
| Obscura Coven Ltd | Wholesale & retail | 2025 |
| Ocean Code AI Ltd | Information & communication | 2026 |
| Ocean Delight Fish and Chips Limited | Hospitality | 2024 |
| OCP (Essex) Limited | Construction | 2006 |
| Octaclean Limited | Administrative & support | 2025 |
| Octalearn Ltd | Education | 2025 |
| October's Rise Limited | Professional & scientific | 2003 |
| Ofar Ltd | Construction | 2017 |
| Office Vision Holdings Limited | Financial services | 2006 |
| Offord Fenning and Associates Limited | Professional & scientific | 1997 |
| Ofodile 2 Health Limited | Health & social care | 2025 |
| Ofstrand Limited | Construction | 2020 |
| Oglretail Ltd | Wholesale & retail | 2026 |
| OHR Property Investments Ltd | Administrative & support | 2018 |