| Number 1 Auto & Valeting Centre Ltd | Wholesale & retail | 2022 |
| Number 8 Cavendish Place Management Company Limited | Households | 1995 |
| Number Nine the Park Limited | Households | 2012 |
| Number One Archers Road Management Committee Limited | Households | 2000 |
| Numbers and More Limited | Professional & scientific | 2013 |
| Numbers Have Meaning Ltd | Professional & scientific | 2023 |
| Numberten Assets Management Ltd | Administrative & support | 2011 |
| Numkam and Daughters Ltd | Real estate | 2021 |
| Nuna Foods Ltd | Wholesale & retail | 2025 |
| Nuonano Limited | Manufacturing | 2018 |
| Nuraltin Ltd | Hospitality | 2025 |
| Nurses UK Franchising Ltd | Administrative & support | 2024 |
| Nurses UK Limited | Administrative & support | 2015 |
| Nurstar Solutions Ltd | Health & social care | 2019 |
| Nurtured Wellbeing Limited | Hospitality | 2014 |
| NUT Hedges Ltd | Professional & scientific | 2014 |
| Nutbourne Property and Development Limited | Construction | 2017 |
| Nutritionpod Limited | Extraterritorial | 2017 |
| Nuts Intl Services Limited | Administrative & support | 2013 |
| Nutshalling Limited | Information & communication | 2017 |
| Nuttree Holdings Limited | Real estate | 2016 |
| Nutz 4X4 Extreme Fabrication Ltd | | 2011 |
| Nuvo Cases Ltd | Wholesale & retail | 2025 |
| Nuvola Distribution Limited | Information & communication | 2010 |
| Nuyu Wellness Clinic Ltd | Other services | 2026 |
| NVD U.K. Limited | Transport & logistics | 2016 |
| Nvyskn Ltd | Wholesale & retail | 2025 |
| NWI Consulting Limited | Financial services | 2018 |
| NX Prime Publishing Ltd | Information & communication | 2025 |
| NXN Surveying Limited | Professional & scientific | 2025 |
| NXT Flooring Limited | Administrative & support | 2024 |
| NXT Solutions Ltd | Information & communication | 2018 |
| NXT Stop Ltd | Wholesale & retail | 2025 |
| Nxtgn Online Limited | Information & communication | 2022 |
| Nyathi Pharm Ltd | Wholesale & retail | 2023 |
| NYK Component Solutions Limited | Transport & logistics | 2007 |
| Nyonic Ltd | Wholesale & retail | 2026 |
| NYX Accounting Limited | Professional & scientific | 2020 |
| Nz-Security Limited | Information & communication | 2015 |
| NZV Transport Ltd | Transport & logistics | 2017 |
| O K Builders Ltd. | Construction | 2017 |
| O M Excavations Ltd | Construction | 2026 |
| O Sable France Ltd | Manufacturing | 2014 |
| O'Brady's Blooms Ltd | Extraterritorial | 2025 |
| O'Briens Eastleigh Ltd | Hospitality | 2023 |
| O'Sullivan Roofing Ltd | Construction | 2022 |
| O.C. Property Maintenance Limited | Construction | 2008 |
| O.Hardie HTS Limited | Wholesale & retail | 2025 |
| OA Carpentry Ltd | Construction | 2025 |
| OAC Recycling Ltd | Wholesale & retail | 2009 |
| Oak & Stone Management Ltd | Transport & logistics | 2025 |
| Oak Couriers Limited | Transport & logistics | 2025 |
| Oak Management Company (Watford) Limited | Households | 1987 |
| Oak School of Motoring Ltd | Education | 2014 |
| Oak Tree Court Hythe Limited | Administrative & support | 2012 |
| Oak Tree Management (Southampton) Limited | Households | 2009 |
| Oak Tree Place (Hedge END) Management Company Limited | Households | 2007 |
| Oak View Homes (I.O.W.) Limited | Wholesale & retail | 2003 |
| Oakdene Construction (UK) Limited | Construction | 2006 |
| Oakdene Court RTM Company Limited | Households | 2024 |
| Oakdene UK Developments Ltd | Construction | 2021 |
| Oakfast Limited | Real estate | 1996 |
| Oakham Grange Limited | Hospitality | 2018 |
| Oakley Build Ltd | Construction | 2019 |
| Oakley Coating Services Ltd | Construction | 2024 |
| Oakley Funeral Planning Ltd | Other services | 2019 |
| Oakley House Owners Company Limited | Hospitality | 2006 |
| Oakley Property Management Limited | Real estate | 2002 |
| Oakley Road Dental Practice Limited | Health & social care | 2019 |
| Oakley Road Garage Ltd | Professional & scientific | 2022 |
| Oakmill Landscaping Ltd | Administrative & support | 2023 |
| Oakmill Projects Ltd | Construction | 2026 |
| Oakmount House Management Company Ltd | Households | 2019 |
| Oakmount Management Limited | Households | 1991 |
| Oakridge Consultancy Limited | Professional & scientific | 2023 |
| Oakridge Property Services Limited | Construction | 2023 |
| Oakridge Property Solutions Ltd | Real estate | 2025 |
| Oakridge Smallholding Limited | Agriculture & fishing | 2010 |
| Oakridge Timber Limited | Wholesale & retail | 2003 |
| Oaks Real Estate Ltd | Real estate | 2024 |
| Oakstead Estates Ltd | Real estate | 2025 |
| Oakview Advisers Ltd | Professional & scientific | 2025 |
| Oakwood Carpenters Limited | Construction | 2020 |
| Oakwood Court Residents Association (Southampton) Limited | Households | 1999 |
| Oakwood Escapes Ltd | Real estate | 2024 |
| Oakwood Management (South) Ltd | Households | 2023 |
| Oase Holding U.K. Limited | Financial services | 2002 |
| Oasis Associates Limited | Professional & scientific | 2018 |
| Oasis Church Southampton Ltd | Other services | 1995 |
| Oasis Southampton Ltd | Hospitality | 2007 |
| OAT Services Limited | Agriculture & fishing | 2001 |
| Oaty Goat Ltd | Hospitality | 2022 |
| OBERT20 Ltd | Public administration | 2024 |
| Objective Management Limited | Professional & scientific | 1986 |
| Observe Care Ltd | Health & social care | 2014 |
| Observium International Limited | Information & communication | 2018 |
| Observium Limited | Information & communication | 2014 |
| Obsessed Automation Management Ltd | Professional & scientific | 2026 |
| Obsidian Compliance Limited | Professional & scientific | 2026 |
| Obsidian Retreats Ltd | Hospitality | 2026 |