| NRV Building & Maintenance Limited | Real estate | 2012 |
| Nssd Limited | Real estate | 2006 |
| NT Financial Limited | Financial services | 2021 |
| NT Medical Ltd | Health & social care | 2013 |
| Nunn Hayward LLP | | 2012 |
| Nuvara Holdings Limited | Financial services | 2025 |
| Nuvara Medicare Limited | Wholesale & retail | 2022 |
| Nyla Properties Ltd | Real estate | 2021 |
| O Downey Limited | Other services | 2013 |
| O&K Holdings Ltd | Real estate | 2018 |
| O.B.A International Ltd | Construction | 2020 |
| Oak END Practice Limited | Real estate | 2022 |
| Oak END Surgery Limited | Health & social care | 2018 |
| Oakhill Road Limited | Real estate | 2016 |
| Oakley Gardens (Bray) Management Company Limited | Professional & scientific | 2008 |
| Oakmount Real Estate Limited | Real estate | 2020 |
| Oaktree Property Management Limited | Real estate | 2019 |
| Oakview Spa Limited | Other services | 2021 |
| OB & Associates Limited | Information & communication | 2021 |
| Octavian Associates II Ltd | Professional & scientific | 2021 |
| Odyssey Management Limited | | 1989 |
| OF Stone and Wood Ltd | Construction | 2024 |
| Oforest Ltd | Manufacturing | 2020 |
| Old Crown Patrimoine Limited | Real estate | 2026 |
| Olga Carpenco Ltd | Administrative & support | 2019 |
| OLI Home Improvements Limited | Construction | 2021 |
| Olivers Opticians Limited | Wholesale & retail | 2002 |
| OM I AM Limited | Other services | 2015 |
| OMC Overseas Medical Consultancy Ltd | Professional & scientific | 2017 |
| Omiyage Limited | Wholesale & retail | 2025 |
| Ommati Limited | Professional & scientific | 2024 |
| One Apple Tree Village Ltd | Real estate | 2026 |
| One Eyed Monster Camera Limited | Professional & scientific | 2012 |
| One Eyed Rabbit Limited | Arts & recreation | 2019 |
| One Fine Solution Ltd | Real estate | 2017 |
| Oneshot.Ai Limited | Information & communication | 2020 |
| Onestrand Shaldon Limited | Real estate | 2017 |
| Online Interactive Research Limited | Professional & scientific | 2006 |
| Onmode Ltd | Information & communication | 2023 |
| ONN Limited | Real estate | 2012 |
| Onstream Limited | Mining & quarrying | 1978 |
| Onthewave Ltd | Administrative & support | 2024 |
| Opal Psychology Ltd | Health & social care | 2022 |
| Open Online Agency Limited | Real estate | 2018 |
| Open Online Limited | Real estate | 2014 |
| Open Property Finance Limited | Real estate | 2014 |
| Open Property Group Limited | Real estate | 2016 |
| Open Trading Limited | Real estate | 2017 |
| Open Trading Two Limited | Real estate | 2021 |
| Openserve Ltd | Information & communication | 2025 |
| Ophthalmic Consultancy Limited | Health & social care | 2015 |
| Optic Haul Ltd | Information & communication | 2023 |
| Optinous Business Research and Consulting Ltd | Information & communication | 2019 |
| Orbier Investments Limited | Professional & scientific | 1990 |
| Orchard Gardens Residents (Chalfont ST Peter) Ltd | Households | 2023 |
| Orchard Park (GX) Management Company Limited | Households | 2021 |
| Organic Chemistry Limited | Extraterritorial | 2012 |
| Organity Ltd | Hospitality | 2023 |
| ORP Investment (UK II) LLP | | 2016 |
| ORP Investment (UK III) LLP | | 2019 |
| Ortman Close (Gerrards Cross) Management Company Limited | Households | 2010 |
| Orvus Consumer Ltd | Manufacturing | 2025 |
| Oscar Scenic Limited | Other services | 2014 |
| Osprey Power Services Limited | Information & communication | 2025 |
| Oswal Neurology Ltd | Health & social care | 2025 |
| Otal Properties Limited | Real estate | 2022 |
| Othala Properties Limited | Real estate | 2020 |
| Othala Short Stays Limited | Real estate | 2023 |
| Otheda Limited | Professional & scientific | 2019 |
| OUM Conscious Health Ltd | Professional & scientific | 2024 |
| OUR Power Design Limited | Professional & scientific | 2026 |
| OUR Power Limited | Wholesale & retail | 2023 |
| Ourdough Limited | Manufacturing | 2025 |
| Owen Agricultural Ltd | Agriculture & fishing | 2018 |
| Oxford Men’S Health Ltd. | Health & social care | 2021 |
| Oxygen Wealth Management Limited | Financial services | 2020 |
| Oyster Two Limited | Hospitality | 2024 |
| OZJ Property Group Ltd | Real estate | 2022 |
| P J Pine & SON Limited | Construction | 2013 |
| P W Auto Centre Ltd | Other services | 2010 |
| P-Chi Services Ltd | Professional & scientific | 2020 |
| P2P4L Ltd | Administrative & support | 2018 |
| P8E Ltd | Manufacturing | 2013 |
| Pacific Corp Ltd | Financial services | 2019 |
| Pacific Securities Limited | Professional & scientific | 1998 |
| Pack and Go Limited | Professional & scientific | 1994 |
| PAD Innovation Limited | Information & communication | 2015 |
| Padel Powerhouse Limited | Arts & recreation | 2024 |
| Paine Financial Services Limited | Financial services | 2018 |
| Painease Ltd | Health & social care | 2024 |
| Palalo Global Consulting Ltd | Administrative & support | 2013 |
| Panacea Pets Limited | Professional & scientific | 2016 |
| Pani Puri House Limited | Hospitality | 2020 |
| Paramount Support Solutions Ltd | Health & social care | 2023 |
| Parchment Document Storage Limited | Administrative & support | 2011 |
| Parchment Law Group LLP | | 2011 |
| Paris & Partners Limited | Professional & scientific | 2026 |
| Park Avenue Properties Limited | Real estate | 2005 |
| Park House Care (Sandy) Limited | Health & social care | 2012 |
| Parkbuild Investments Ltd | Real estate | 2018 |