| Oakbrook Freehold Limited | Households | 2019 |
| Oakbrook Residents Association Limited | Households | 2007 |
| Oakdene Products Ltd | Wholesale & retail | 2015 |
| Oakdene Professional Services Ltd | Real estate | 2026 |
| Oakes Home Management Ltd | Manufacturing | 2023 |
| Oakfield (Crawley) Management Company Limited | Households | 2003 |
| Oakfield Court 2 (Bradley Stoke) Management Company Limited | Households | 2002 |
| Oakfields Consultancy Ltd | Professional & scientific | 2024 |
| Oakhill Meadow Management Company Limited | Households | 2026 |
| Oakhurst Court (Freehold) Limited | Households | 2005 |
| Oakhurst Court Residents Management Company Limited | Households | 2003 |
| Oakland Development 2015 Limited | Real estate | 2015 |
| Oakleigh Gates Limited | Construction | 2011 |
| Oakley Landscapes Limited | Administrative & support | 2005 |
| Oakley Manor House Ltd | Real estate | 2023 |
| Oakley Renovations South East Ltd | Construction | 2023 |
| Oakman Pamphylia Limited | Administrative & support | 2018 |
| Oakvale UK Limited | Real estate | 2006 |
| Oakwood Property Consultants Ltd | Administrative & support | 2019 |
| Ocallaghan RIG Ltd | Construction | 2025 |
| OCD Cleaning London Limited | Administrative & support | 2017 |
| Ocean Architecture Ltd | Professional & scientific | 2023 |
| Ocean Business Ltd | Administrative & support | 2024 |
| Oceanic Pawel Poniatowski Limited | Construction | 2007 |
| ODE Trades Limited | Construction | 2022 |
| OFF Court Studio Ltd | Wholesale & retail | 2026 |
| Office Land Solutions UK Limited | Wholesale & retail | 2025 |
| Office Power Limited | Wholesale & retail | 2012 |
| Ofiom Care Limited | Health & social care | 2026 |
| OH My Pleasure Ltd | Wholesale & retail | 2025 |
| Ohbro Properties Limited | Real estate | 2022 |
| Olag Development Limited | Construction | 2021 |
| Old School Mews Management Company Limited | Real estate | 1999 |
| Oldencraig Mews Management Company Limited | Households | 2022 |
| Olima (London) Limited | Health & social care | 2017 |
| Oliver Charles Ltd | Manufacturing | 2016 |
| Oliver James Developments Limited | Real estate | 2015 |
| Olivia Sofia Austin Limited | Extraterritorial | 2016 |
| Olugbolahan Onibuwe-Johnson Ltd | Financial services | 2020 |
| Omnee 360 Ltd | Information & communication | 2025 |
| Omnia Solutions Ltd | Administrative & support | 2020 |
| ON Circuit Cars Limited | Wholesale & retail | 2017 |
| ON Circuit Limited | Wholesale & retail | 2016 |
| ON the DOT Technologies Limited | Information & communication | 2015 |
| Onclick Lifestyle Ltd | Arts & recreation | 2020 |
| One Cent Barbers Ltd | Other services | 2021 |
| One Cent Group Limited | Financial services | 2022 |
| One Cent Hire Limited | Administrative & support | 2019 |
| One Cent Ltd | Construction | 2014 |
| One Cent Properties Limited | Construction | 2022 |
| One Cent Spa Ltd | Other services | 2021 |
| One Horsham Gates Management Company Limited | Households | 2016 |
| One Take Pictures Limited | Information & communication | 2003 |
| One Thousand and One Ltd | Professional & scientific | 2024 |
| Onera Limited | Wholesale & retail | 2025 |
| Only Extractor Fans Ltd | Construction | 2025 |
| Onscore Limited | Information & communication | 2021 |
| Oomman Creations Limited | Information & communication | 2023 |
| Opal & Co. Cleaning Ltd | Administrative & support | 2025 |
| Open Palm Care Ltd | Health & social care | 2024 |
| Opes Financial Partners Limited | Administrative & support | 2011 |
| Optimised Living Limited | Professional & scientific | 2017 |
| Optimum Cars Limited | Transport & logistics | 2016 |
| Opting for Health Ltd | Wholesale & retail | 2024 |
| Optomation Limited | Information & communication | 2014 |
| Oranbell Limited | Professional & scientific | 2019 |
| Orchard House (1991) Limited | Households | 1991 |
| Orchard Property Maintenance Limited | Administrative & support | 2025 |
| Orchids Pastry Ltd | Wholesale & retail | 2020 |
| Orion Cloud Solutions Ltd | Information & communication | 2024 |
| Orion House Management Limited | Households | 2005 |
| Orix Chase Ltd | Professional & scientific | 2017 |
| Orlanix Limited | Construction | 2003 |
| Orly Limited | Administrative & support | 2013 |
| Ornelossi Limited | Wholesale & retail | 2025 |
| Oscar Romeo Aviation Limited | Arts & recreation | 1991 |
| Oschan Ltd | Wholesale & retail | 2015 |
| Outdoor Solutions Limited | Administrative & support | 2024 |
| Outlier Creative Agency Ltd | Information & communication | 2025 |
| Outset Design Studio Ltd | Professional & scientific | 2018 |
| Outwood Cricket Club | Arts & recreation | 2007 |
| Overseas Moving Network International Limited | Other services | 1986 |
| Overxceed Ltd | Information & communication | 2020 |
| Owens Accountancy Ltd | Administrative & support | 2013 |
| Oxford Eden Medical and Science Limited | Health & social care | 2024 |
| Oxgrid Ltd | Information & communication | 2023 |
| Oxted Developments (2007) Limited | Construction | 2007 |
| Oxted Developments (2008) Limited | Construction | 2007 |
| Oxted Land Company Limited | Construction | 2007 |
| Oxted Residential Limited | Construction | 2007 |
| Oxwich Accountancy Limited | Professional & scientific | 2018 |
| Ozka Services Ltd | Information & communication | 2024 |
| P & B Services Limited | Wholesale & retail | 2002 |
| P & C Services (Gatwick) Limited | Professional & scientific | 1998 |
| P & D Property Developers Limited | Construction | 2006 |
| P Hudd Ltd | Real estate | 2024 |
| P&R Roofing and Building Ltd Ltd | Construction | 2025 |
| P.G.M.Agencies Limited | Construction | 1966 |
| PAC Executive Cars Limited | Transport & logistics | 2011 |
| PAC Investments Limited | Construction | 2001 |