| Nutbrown Properties Ltd | Real estate | 1999 |
| Nutmeg Coffee Ltd | Hospitality | 2022 |
| Nutritional Focus Ltd | Information & communication | 2013 |
| Nutritional Insight Limited | Information & communication | 2014 |
| Nuvanta Ventures Limited | Wholesale & retail | 2025 |
| NV Management (EUR) Ltd | Households | 2018 |
| Nvst.Ai Ltd | Information & communication | 2018 |
| NW Properties (Surrey) Limited | Real estate | 2022 |
| Nxus Drinks Limited | Wholesale & retail | 1990 |
| Nxus Holdings Limited | Financial services | 1986 |
| Nxus Properties Ltd | Real estate | 2025 |
| NY Cafe One Limited | Hospitality | 2015 |
| NY Consultancy Limited | Professional & scientific | 2008 |
| O & O Simuan Ltd | Real estate | 2020 |
| O&F Consultancy Limited | Real estate | 2024 |
| O&R Trading UK Ltd | Real estate | 2019 |
| O'Callaghan Consulting Ltd | Professional & scientific | 2013 |
| O'Reilly Barrington Watkis Ltd | Extraterritorial | 2024 |
| O.D.A. - Optimum Derma Aciditate Ltd | Wholesale & retail | 2012 |
| Oak Glade Management Ltd | Households | 2015 |
| Oak Road Ventures Ltd | Professional & scientific | 2023 |
| Oakdene Flooring Limited | Construction | 2016 |
| Oaklands Management (Tadworth) Limited | Households | 2007 |
| Oaklee Consultancy Ltd | Extraterritorial | 2007 |
| Oakleigh Residents' Association Limited | Other services | 1968 |
| Oaks (Sutton) Management Co. Limited(The) | Real estate | 1977 |
| Oaks View Property Management Ltd | Real estate | 2019 |
| Oakshade Mews Limited | Real estate | 2023 |
| Oakspear Limited | Administrative & support | 1982 |
| Oakton Developments (Epsom) Limited | Construction | 2020 |
| Oakton Developments (Surrey) Limited | Construction | 2007 |
| Oakton Developments Limited | Construction | 2002 |
| Oakwood Building Contractors Limited | Construction | 1986 |
| Oatlands Computer Services Limited | | 1978 |
| OB One Limited | Information & communication | 2018 |
| Obriens Decorating Services Ltd | Construction | 2025 |
| OBS Care Ltd | Education | 2021 |
| Obsidian Surveying Ltd | Construction | 2020 |
| OC Design and Build Ltd | Construction | 2016 |
| OC9 Ltd | Real estate | 2008 |
| Oceans Marine Group Ltd | Professional & scientific | 2022 |
| Oconcept Limited | Manufacturing | 2022 |
| Octagon (Coombe Lane) Management Company Limited | Households | 2008 |
| Octavia Sloane Ltd | Professional & scientific | 2026 |
| Odililight Limited | Wholesale & retail | 2026 |
| ODK Developments Limited | Real estate | 2025 |
| Odyssey Plunge Ltd | Wholesale & retail | 2024 |
| OE Parts 247 Ltd | Wholesale & retail | 2019 |
| Oeeg Consulting Limited | Real estate | 2024 |
| OFF Balance Ltd | Wholesale & retail | 2025 |
| Office of Everyone Limited | Information & communication | 2022 |
| Offshore Consulting Group Limited | Professional & scientific | 2015 |
| Ogafill AI Limited | Information & communication | 2025 |
| OGI Trade Ltd | Wholesale & retail | 2020 |
| Ogle HOG Limited | Information & communication | 2011 |
| Ohoo Limited | Professional & scientific | 2019 |
| OJW Building Services Ltd | Construction | 2025 |
| Okorefe Investment Properties Ltd | Real estate | 2025 |
| Old Court Lodge Limited | Health & social care | 2013 |
| Old Lodge (Holdings) Limited | Real estate | 1955 |
| Old Schools Court Management Company (Ewell) Limited | Households | 1991 |
| Old Vicarage Elsenham Limited | Construction | 2025 |
| Oldfield Apartments Management Company Limited | Households | 1995 |
| Oldfield Management Company Limited | Households | 1995 |
| Olimpo Holdings Ltd | Financial services | 2021 |
| Olive SMI Ltd | Wholesale & retail | 2014 |
| Oliver Edwards Developments Limited | Construction | 2017 |
| Oliver Sanderson Group PLC | Extraterritorial | 2015 |
| Oliver Sanderson Limited | Administrative & support | 2011 |
| Olivers Contracts Limited | Construction | 2016 |
| Olivian Homes Ltd | Health & social care | 2020 |
| Ombrello Limited | Financial services | 2025 |
| Omgc Ltd | Professional & scientific | 2016 |
| Omni Pics Ltd | Information & communication | 2024 |
| Omnia Partners Limited | Professional & scientific | 2016 |
| ON a Quest Limited | Wholesale & retail | 2023 |
| ON Beat Social Ltd | Professional & scientific | 2024 |
| ON Point for Business Limited | Professional & scientific | 2026 |
| ON Target Recruitment Limited | Administrative & support | 1993 |
| ON the Rise Access Training Limited | Education | 2024 |
| ON Top Barbers Ltd | Other services | 2026 |
| On-Maintenance Ltd | Construction | 2025 |
| Onabo Consulting Limited | Information & communication | 2002 |
| One Bridge Street Management Limited | Households | 2020 |
| One Five Ltd | Administrative & support | 2009 |
| One Future YOU Ltd | Other services | 2022 |
| One Hundred Partnerships Limited | Professional & scientific | 2008 |
| Onehundred Partnerships Holdings Limited | Financial services | 2024 |
| Oneputt Real Estate Ltd | Real estate | 2020 |
| Oneten Investment Limited | Real estate | 2018 |
| Online Club Ltd | Other services | 2025 |
| Only Boilers London Limited | Construction | 2023 |
| Ontoppropertymaintenance Ltd | Households | 2026 |
| Ontrsh Ltd | Wholesale & retail | 2025 |
| Onva Consulting Limited | Professional & scientific | 2008 |
| Oomisoft Limited | Information & communication | 2018 |
| Oottupura Ewell Ltd | Hospitality | 2020 |
| Opalux Ltd | Wholesale & retail | 2025 |
| Open Focus Attention Training Limited | Health & social care | 2016 |
| Opportune City Resources Limited | Administrative & support | 2010 |