| NUR Property Management Ltd | Real estate | 2026 |
| Nutriact Limited | Health & social care | 2019 |
| Nutrion News Network Ltd | Extraterritorial | 2019 |
| Nutrition Facts Ltd | Extraterritorial | 2020 |
| NV Decor Ltd | Construction | 2026 |
| NVD Contracts Limited | Real estate | 2016 |
| NVD Developments Limited | Real estate | 2006 |
| NVD Limited | Wholesale & retail | 1998 |
| NW Construction Services Ltd | Construction | 2018 |
| Nyon Associates Limited | Professional & scientific | 2012 |
| Nyon Investments Limited | Financial services | 2022 |
| NYPIZZA55 Ltd | Hospitality | 2025 |
| NZH Properties Ltd | Real estate | 2026 |
| NZO Consulting Limited | Professional & scientific | 2022 |
| O & G Services Limited | Construction | 2018 |
| O & M Buildings Limited | Construction | 2025 |
| O Holdings Ltd | Professional & scientific | 2024 |
| O'Connor Engineering Limited | Construction | 2005 |
| O'Donnell Construction Management Limited | Construction | 2013 |
| OA Skillbridge Ltd | Information & communication | 2025 |
| OA2 Property Limited | Real estate | 2022 |
| Oadigitals Ltd | Information & communication | 2023 |
| Oak & Rose Properties Limited | Real estate | 2025 |
| Oak Avenue Management Company Limited | Households | 2008 |
| Oakdale Garage Limited | Mining & quarrying | 2004 |
| Oakenshaw Kennels Ltd | Agriculture & fishing | 2019 |
| Oakes Limited | Professional & scientific | 2006 |
| Oakes Sargent Properties Ltd | Real estate | 2025 |
| Oakhurst Court Holdings Limited | Professional & scientific | 2010 |
| Oakhurst Court Limited | Health & social care | 1994 |
| Oakland and Albion Properties Ltd | Real estate | 2024 |
| Oakleigh Property Holdings LLP | | 2021 |
| Oakley Decorating Contractors Ltd | Construction | 2024 |
| Oakline Goods Ltd | Wholesale & retail | 2025 |
| Oakmoon Properties Limited | Financial services | 2018 |
| Oaks Rock Consultancy Limited | Professional & scientific | 2024 |
| Oaks Rock Property Ltd | Real estate | 2017 |
| Oakwood Commercial Ltd | Real estate | 2023 |
| Oakwood House Developments Limited | Construction | 2013 |
| Oakwood Portfolio Services Ltd | Real estate | 2025 |
| Oana Trans Ltd | Transport & logistics | 2019 |
| Oasis Pathways Ltd | Health & social care | 2025 |
| Oates Contracting Services Limited | Wholesale & retail | 1996 |
| Oberbrambach Ltd. | Administrative & support | 2011 |
| Obikev Limited | Health & social care | 2014 |
| OBS Electrical Installations & Testing Limited | Construction | 2016 |
| Obscure Drinks Co Ltd | Manufacturing | 2024 |
| Obsession Transport Services Ltd | Transport & logistics | 2022 |
| Obsessiveholdings Ltd | Financial services | 2025 |
| Obsessiveproperty Ltd | Real estate | 2025 |
| OC Graphics Ltd | Manufacturing | 2014 |
| Ocean Drive Tyres Ltd | Wholesale & retail | 2026 |
| Ocean Drive Valet Ltd | Administrative & support | 2015 |
| OCR Medical Services Limited | Health & social care | 2025 |
| Octc Limited | Other services | 2011 |
| Octopus Services Ltd | Administrative & support | 2017 |
| Oculus Building Consultancy Limited | Administrative & support | 1997 |
| Ocuzen Ltd | Health & social care | 2024 |
| Odabj Group Ltd | Information & communication | 2024 |
| ODM Europe Ltd | Wholesale & retail | 2012 |
| Odoma Care Limited | Health & social care | 2018 |
| Odyssey Inns Ltd | Hospitality | 2021 |
| OE Electrics Limited | Manufacturing | 1993 |
| OEM Engine Solutions Ltd | Manufacturing | 2026 |
| Oewe Ltd | Wholesale & retail | 2020 |
| OFF the PEG Bridal Limited | Extraterritorial | 2018 |
| OFF the PEG Bridal Outlet Limited | Wholesale & retail | 2022 |
| Office Electrics Limited | Manufacturing | 1986 |
| Office TEK Solutions Ltd | Other services | 2017 |
| Official Opulentia Ltd | Wholesale & retail | 2024 |
| Ogden Developments Ltd | Construction | 2025 |
| OH K Yorkshire Ltd | Wholesale & retail | 2026 |
| Ohana Liahona Investments Ltd | Real estate | 2025 |
| OHL Properties London Limited | Households | 2019 |
| OJ Contracting Limited | Energy | 2008 |
| OJC Plastering Ltd | Construction | 2026 |
| Okentertainment Ltd | Arts & recreation | 2023 |
| Old Forge Motor Group Ltd | Wholesale & retail | 2019 |
| Old Studios Ltd | Information & communication | 2026 |
| Oldenburg Limited | Administrative & support | 2002 |
| Oldroyd Property Maintenance Ltd | Construction | 2025 |
| Olena Consulting Limited | Information & communication | 2011 |
| Oliive Branch Limited | Real estate | 2021 |
| Olive & Meze Limited | Hospitality | 2014 |
| Olive Homes Group Ltd | Real estate | 2024 |
| Oliver Dean Hair & Beauty Limited | Other services | 2016 |
| Oliver Homes & Estates Ltd | Real estate | 2024 |
| Oliver Norton Ltd | Construction | 2026 |
| Oliver Tennant Ltd | Education | 2019 |
| Oliver Vaughn Group Ltd | Wholesale & retail | 2025 |
| Oliver Ward Trading Ltd | Professional & scientific | 2026 |
| Oliver William Ecommerce Ltd | Wholesale & retail | 2024 |
| Olivier Catering Ltd | Hospitality | 2024 |
| OM Devi ADK Anaesthesia Limited | Health & social care | 2018 |
| OM Medicus Ltd | Health & social care | 2021 |
| OM Spark&Shine Limited | Administrative & support | 2026 |
| Oman Electrical Services Ltd | Construction | 2026 |
| OMB Surplus Ltd | Wholesale & retail | 2025 |
| Omega Retail Services Limited | Construction | 2023 |
| Omega-Independent Ltd | Wholesale & retail | 2024 |