| NRG Management Limited | Real estate | 2025 |
| NRG Property Solutions Limited | Construction | 2008 |
| NSK Limited | Health & social care | 1968 |
| NT Consulting (UK) Ltd | Professional & scientific | 2012 |
| NTL Investments Limited | Real estate | 2022 |
| Nucare Maintenance Ltd | Administrative & support | 2013 |
| Nucrest Holdings Limited | Wholesale & retail | 2018 |
| Nucrest Limited | Wholesale & retail | 1983 |
| Nuivio Ventures UK Ltd | Administrative & support | 2020 |
| Numan Dental Ltd | Health & social care | 2024 |
| Number SIX Services Ltd | Information & communication | 2026 |
| Numerical (HR) Ltd | Administrative & support | 2018 |
| Numerical Group Ltd | Financial services | 2018 |
| Numerical Insights Ltd. | Professional & scientific | 2014 |
| Numid Limited | Professional & scientific | 2018 |
| Nuontec Limited | Real estate | 2021 |
| Nursery Holdings (ST Leonards) Limited | Education | 2016 |
| Nursery Holdings Limited | Education | 2017 |
| Nutberry Limited | Manufacturing | 1978 |
| Nutbourne Medical Ltd | Health & social care | 2021 |
| Nutriat Limited | Health & social care | 2013 |
| Nutrition Matrix Ltd | Health & social care | 2020 |
| Nutritional Therapy Education Commission | Other services | 2013 |
| Nutritotal Limited | Health & social care | 2024 |
| Nuvision Energy Limited | Administrative & support | 2009 |
| Nuwux Ltd | Information & communication | 2013 |
| NVE Technologies Limited | Extraterritorial | 2009 |
| NVO Group Ltd | Wholesale & retail | 2026 |
| NW Biopharm Consulting Limited | Professional & scientific | 2021 |
| NWR Engineering Ltd | Professional & scientific | 2026 |
| Nxtgen Football Academy Limited | Education | 2023 |
| NXY Holdings Limited | Real estate | 2021 |
| NYE Construction Limited | Construction | 2021 |
| O'Brien & Ivanovic Ltd | Professional & scientific | 2006 |
| O'Connor & Co Accountants Limited | Professional & scientific | 2025 |
| O'Gorman Installation Technology Limited | Information & communication | 1998 |
| O.A.M. Holdings Limited | Financial services | 2010 |
| Oakgood (1992) Limited | Real estate | 1992 |
| Oakgreen Developments Limited | Construction | 1996 |
| Oaklands Dental Limited | Health & social care | 2026 |
| Oaklands Surveying Ltd | Professional & scientific | 2011 |
| Oakley Down Management Company Limited | Real estate | 2010 |
| Oakmoor Group Ltd | Financial services | 2025 |
| Oakwell Property and Lettings Limited | Real estate | 2022 |
| Oakwood Court Residents Association Limited | Households | 1994 |
| Oasis Sauna Limited | Other services | 2024 |
| OAT Coffee Limited | Hospitality | 2019 |
| Obalade Locum Services Ltd | Wholesale & retail | 2019 |
| Obiter Limited | Other services | 1999 |
| Objective Nutrition Limited | Administrative & support | 2019 |
| Observatory Falmouth Limited | Health & social care | 2021 |
| Ocean One Interiors Limited | Construction | 2014 |
| Ocean Village Dental Clinic Ltd | Health & social care | 2021 |
| Oceanwise Limited | Administrative & support | 2010 |
| Octohill Invest Ltd | Real estate | 2026 |
| Oculi Dente Ltd | Health & social care | 2022 |
| Odonti Limited | Health & social care | 2013 |
| ODS Consultants Limited | Manufacturing | 2024 |
| Office Consumables Limited | Wholesale & retail | 2025 |
| Office of Chris Berry Limited | Professional & scientific | 2001 |
| Officemaid Commercial Cleaning Limited | Administrative & support | 2021 |
| OFH Bricks Ltd | Real estate | 2020 |
| OFH Ltd | Health & social care | 2019 |
| OG Sportswear UK Limited | Wholesale & retail | 2025 |
| OGD Limited | Construction | 2006 |
| Ogden & Harris Electrical Services Ltd | Construction | 2019 |
| Ogden Electrical Services Limited | Extraterritorial | 2008 |
| Oglesbyarborist Services Ltd | Agriculture & fishing | 2024 |
| Ohcs 5 DEF Limited | Wholesale & retail | 2022 |
| Ohcs High Street Ltd | Real estate | 2021 |
| Ohcs Limited | Financial services | 2013 |
| Ohcs TW3 Limited | Real estate | 2017 |
| Oinkly Limited | Professional & scientific | 2025 |
| OJ Medical Limited | Health & social care | 2015 |
| Ojeu Finder Ltd | Information & communication | 2013 |
| OJR Trading Ltd | Financial services | 2018 |
| OK Partners Ltd | Wholesale & retail | 2025 |
| Okeze Holdings Ltd | Financial services | 2012 |
| OKI Sauna & Wellness Limited | Other services | 2026 |
| Old Orchard Clinic (Sussex) Limited | Health & social care | 2012 |
| Old Orchard Clinic Limited Liability Partnership | | 2012 |
| Old Toad Studio Ltd | Wholesale & retail | 2024 |
| Old Town Corner Shop Ltd | Wholesale & retail | 2026 |
| Old Town Electrical Limited | Construction | 2015 |
| Old Town Electrics Limited | Construction | 2016 |
| Old Town Garage Services Limited | Wholesale & retail | 2023 |
| Old Town Holdings Limited | Professional & scientific | 2024 |
| Old Town Properties Limited | Real estate | 2016 |
| Old Town Shop Ltd | Wholesale & retail | 2025 |
| Old Town Trader Ltd | Real estate | 2025 |
| Old Vicarage Close Management Company 2010 Limited | Households | 2010 |
| Old Vicarage Close Management Company 2015 Limited | Households | 2015 |
| Old Vicarage Management Company (Eastbourne) Limited | Households | 2004 |
| Oldany Estate Ltd | Real estate | 2022 |
| Oliphantstreet Ltd | Professional & scientific | 2026 |
| Oliver & Andreea Care Ltd | Administrative & support | 2017 |
| Olivia Butler & Co Limited | Other services | 2018 |
| Olivo Property Management Ltd | Real estate | 2025 |
| Ollie's Army Garden & Landscaping Ltd | Administrative & support | 2024 |
| Olokun Store Ltd | Wholesale & retail | 2021 |