| Nuliv Ltd | Construction | 2024 |
| Number Eleven Partnership Ltd | Administrative & support | 2013 |
| Nuralex Ltd | Information & communication | 2026 |
| NV Intex Ltd | Administrative & support | 2025 |
| Nwabueze Limited | Health & social care | 2025 |
| O Pamplet Ltd | Hospitality | 2026 |
| O&D Hartington Limited | Construction | 2020 |
| O&D London Ltd | Real estate | 2018 |
| O'Dea Property Services Limited | Households | 2023 |
| O'Donoghue Plant Hire Limited | Professional & scientific | 1995 |
| Oak Mason Properties Ltd | Real estate | 2025 |
| Oakhill Estate Agents Limited | Real estate | 2012 |
| Obiakor Ltd | Health & social care | 2019 |
| Ocean Energy Ltd | Construction | 2019 |
| Ocean Solutions Business Developments Limited | Information & communication | 2006 |
| Octava Ltd | Construction | 2019 |
| Oculus-Developments Limited | Real estate | 2013 |
| Odeon Parade RTM Company Limited | Households | 2024 |
| OH Happy J Productions Ltd | Information & communication | 2024 |
| OH Mycar Limited | Wholesale & retail | 2024 |
| Ohmyvin Ltd | Wholesale & retail | 2026 |
| OJ Gaming Limited | Information & communication | 2025 |
| Old School Court Management (1993) Limited | Real estate | 1993 |
| Oleh Deineko Limited | Construction | 2025 |
| Olteanu Building Limited | Construction | 2019 |
| OM Property Solutions Ltd | Construction | 2025 |
| OM Tribe Retreats Ltd | Administrative & support | 2022 |
| OMI ENT Ltd | Administrative & support | 2021 |
| OMI Studios Limited | Information & communication | 2024 |
| Omica Gill Investments Limited | Real estate | 2024 |
| Omid Car Sales Ltd | Wholesale & retail | 2023 |
| Omni Ecotech and Logistics PVT. Ltd | Professional & scientific | 2012 |
| ON Board Defence Ltd | Wholesale & retail | 2002 |
| ON Call Services 247 Ltd | Professional & scientific | 2021 |
| ON Command Automation & Electrical Ltd | Construction | 2026 |
| ON the FLY Limited | Administrative & support | 2021 |
| ONA Limited | Real estate | 2026 |
| Once a Year in London Ltd | Wholesale & retail | 2023 |
| Ondemand Detailing Ltd | Wholesale & retail | 2018 |
| One Central Park Limited | Real estate | 2019 |
| One RUH Ltd | Hospitality | 2020 |
| One Stop Arts Ltd | Information & communication | 2022 |
| Onecarthub Limited | Wholesale & retail | 2026 |
| Oneday Coffee Ltd. | Wholesale & retail | 2024 |
| Onemli Rental Properties Ltd | Real estate | 2025 |
| Oneplace Ecommerce Ltd | Wholesale & retail | 2022 |
| Onesite Ltd | Construction | 2014 |
| Onesquarefoot Ltd | Real estate | 2019 |
| Online Accountancy & Business Solutions Ltd | Professional & scientific | 2024 |
| Online Retail Services Limited | Wholesale & retail | 2024 |
| Onslow Gardens Consulting Ltd | Professional & scientific | 2018 |
| Onyx Growth Limited | Wholesale & retail | 2025 |
| Onyx Homes Ltd | Real estate | 2022 |
| Onyx Property Holdings Limited | Financial services | 2025 |
| Oola Lingerie Limited | Wholesale & retail | 2020 |
| Open House Agents Limited | Real estate | 2019 |
| Opus INT Ltd | Construction | 2025 |
| Orange Tree House Consulting Ltd | Information & communication | 2022 |
| Orca Ventures AI Limited | Information & communication | 2026 |
| Orchid Management Community Services CIC | Manufacturing | 2026 |
| Orchid Management PVT Ltd | Hospitality | 2017 |
| Orchid Trading Group Ltd | Wholesale & retail | 2024 |
| Oregan Developments Limited | Real estate | 2015 |
| Oregan Homes Limited | Real estate | 2018 |
| Orion's Plan Ltd | Information & communication | 2024 |
| Orleans Garden Kiosk Ltd | Wholesale & retail | 2012 |
| Ormiston Wire Limited | Manufacturing | 1923 |
| Orpington Management Company Ltd | Construction | 2018 |
| Oshey Expressions Ltd. | Wholesale & retail | 2017 |
| Osterley Alliance Ltd | Real estate | 2022 |
| Osterley Construction Ltd | Construction | 2013 |
| Osterley Development Services Limited | Real estate | 2018 |
| Osterley Holdings Limited | Construction | 2019 |
| Osterley Homes Ltd | Real estate | 2010 |
| Osterley Lettings Ltd | Real estate | 2013 |
| Osterley Lodge Limited | Households | 1999 |
| Osterley Ltd | Real estate | 2018 |
| Osterley Park Group Limited | Transport & logistics | 2021 |
| Osterley Personal Training Limited | Arts & recreation | 2016 |
| Osterley Properties Limited | Real estate | 2024 |
| Osterley Strategic Finance Ltd | Professional & scientific | 2026 |
| Othia Consulting Ltd | Professional & scientific | 2025 |
| Ottar Hub Ltd | Wholesale & retail | 2023 |
| Otterworth Management Limited | Real estate | 2017 |
| Ovations Corp Limited | Construction | 2013 |
| Ozen Electronic and Engineering Ltd | Professional & scientific | 2021 |
| Ozky Ltd. | Information & communication | 2017 |
| P & R Fabrications Limited | Manufacturing | 1996 |
| P and D UK Services Limited | Transport & logistics | 2018 |
| P Croft Property Limited | Households | 2025 |
| P S Plumbing Limited | Construction | 2015 |
| P&A Wealth Management Limited | Real estate | 2024 |
| P&M Meats Ltd | Wholesale & retail | 2025 |
| P&So Properties Limited | Real estate | 2022 |
| P.A. Seccombe & SON, Limited | Wholesale & retail | 1934 |
| P.R.S Property Management Ltd | Real estate | 2022 |
| P09 Property Management Limited | Real estate | 2019 |
| P3RRY Productions Ltd | Information & communication | 2013 |
| Paarus Consulting Ltd | Information & communication | 2013 |
| Paau MAA DEI Limited | Professional & scientific | 2022 |