| One Step Science Limited | Professional & scientific | 2011 |
| Online Corporation Limited | Information & communication | 1997 |
| Onlink Limited | Professional & scientific | 2003 |
| Onyx Presentations Limited | Arts & recreation | 1991 |
| Ooho Consultancy Ltd | Information & communication | 2015 |
| Opalcare Limited | Health & social care | 1996 |
| Open Answers Limited | Information & communication | 1993 |
| Openair Menswear Limited | Wholesale & retail | 2004 |
| Opera Opera Opticians Limited | Wholesale & retail | 1984 |
| Oprro Limited | Professional & scientific | 2007 |
| Opticiancall Limited | Wholesale & retail | 1998 |
| Optik Limited | Arts & recreation | 1981 |
| Optimal Solutions 4U Limited | Professional & scientific | 2000 |
| Optimus Consultancy Limited | Professional & scientific | 1998 |
| Optimus Limited | Professional & scientific | 1979 |
| Optipharm (Opticians) Ltd | Wholesale & retail | 1979 |
| Optom Ltd | Wholesale & retail | 2004 |
| Optomlink Limited | Health & social care | 1999 |
| Optprize Limited | Real estate | 1979 |
| Opus Industrial Development & Design Limited | | 1970 |
| Orange Sky Services Limited | Other services | 2006 |
| Orangejuice Advertising Limited | Other services | 2003 |
| Orapay Consulting Services Limited | Information & communication | 2005 |
| Orbany Limited | Information & communication | 1997 |
| Orch Investments Limited | Real estate | 2004 |
| Orchid Student Living Coventry Ltd | Construction | 2025 |
| Orchid Student Living Swansea Ltd | Real estate | 2025 |
| Oregano Limited | Hospitality | 1998 |
| Oreka Kids Limited | Manufacturing | 2000 |
| Oriental (Newspapers) Limited | Manufacturing | 1993 |
| Original Blue Limited | Manufacturing | 1994 |
| Original Taste of Pakistan Limited | Hospitality | 2013 |
| Original Windows Limited | Construction | 2002 |
| Origma Limited | Wholesale & retail | 1995 |
| Orley Farm School Enterprises Limited | Real estate | 2005 |
| ORM Properties UK Ltd | Real estate | 2001 |
| Oscar Krane (Operations) Ltd | Administrative & support | 2022 |
| Osmington House Management Company Ltd | Real estate | 2004 |
| Ostara London Limited | Wholesale & retail | 2021 |
| Osterley Park Farm Limited | Agriculture & fishing | 1957 |
| OT Enterprises Ltd | Information & communication | 2003 |
| Otaaki UK Limited | Manufacturing | 2022 |
| Ottimo Eatery Ltd | Hospitality | 2021 |
| Ottoman Silks Limited | Wholesale & retail | 2004 |
| Otvale Limited | Construction | 1977 |
| OUT UK Limited | Information & communication | 2000 |
| Outerscan Limited | Information & communication | 1988 |
| Overseas Business Enterprises Limited | | 1982 |
| Oxford Care Homes Limited | Health & social care | 2001 |
| Oxhey Homes Ltd | Real estate | 2024 |
| Oyster Capsule Consulting Ltd | Professional & scientific | 2024 |
| OZ Direct Limited | Administrative & support | 2003 |
| Oz-Su Limited | Hospitality | 2008 |
| OZZ & DEN Ltd | Hospitality | 2017 |
| OZZ Off-Licence Ltd | Wholesale & retail | 2026 |
| P Madan Ltd | Professional & scientific | 2011 |
| P W Cleaning Services Limited | Other services | 2002 |
| P&R Fitness Ltd | Arts & recreation | 2017 |
| P. Donaghey Limited | Construction | 2001 |
| P. Goddard & Sons (Transport) Limited | Other services | 1982 |
| P. J. Light Haulage Limited | Transport & logistics | 2003 |
| P. Rose (Uxbridge) Limited | Wholesale & retail | 2012 |
| P.B.C.Limited | Arts & recreation | 1936 |
| P.B.L. (Jewellers) Limited | Wholesale & retail | 1978 |
| P.C. Harris Limited | Real estate | 1962 |
| P.J. Shah Associates Limited | Professional & scientific | 1998 |
| P.J.Assurance Agency Limited | Financial services | 1985 |
| P.R.O.V.E Communications Limited | Information & communication | 2001 |
| P.R.S. (London) Limited | Real estate | 2002 |
| PA Property Solutions Ltd | Real estate | 2016 |
| Pa.Pa Joe's 100 Ltd | Arts & recreation | 2002 |
| Paaren Limited | Professional & scientific | 2001 |
| Pace Sports Management LLP | | 2004 |
| Pacific Court Ltd | Real estate | 2017 |
| Padae Ltd | Wholesale & retail | 2025 |
| Padierna Properties Limited | Real estate | 2025 |
| Padma Dimension Limited | Information & communication | 2024 |
| Padwicks Travel (Wembley) Limited | Administrative & support | 1981 |
| Page Close Limited | Households | 1998 |
| Paige & Petrook Limited | Real estate | 2006 |
| Palaeodate Limited | Mining & quarrying | 2004 |
| Palmerston Industries Limited | Real estate | 1991 |
| Palmpress Limited | | 1981 |
| Palmtrend Limited | Extraterritorial | 1986 |
| Pan-Asia Management and Industrial Company Limited | Extraterritorial | 2002 |
| Panas Products Limited | Wholesale & retail | 1994 |
| Panda.Co Designs Limited | Manufacturing | 2005 |
| Panelwide Limited | Financial services | 2004 |
| Paper White Limited | Administrative & support | 2002 |
| Paps Enterprises Limited | Information & communication | 2001 |
| Papworth Specialist Vehicles Limited | | 1995 |
| Parallel Applications Ltd | Extraterritorial | 1988 |
| Paramount Enterprises UK Limited | Real estate | 2002 |
| Paramount Plants and Gardens Limited | Wholesale & retail | 2005 |
| Paranthan Union Ltd | Other services | 2016 |
| Paraspar Limited | Information & communication | 1997 |
| Paratech Limited | Information & communication | 1996 |
| Pardhan Niwas Ltd | Real estate | 2025 |
| Pardis Design & Construction Ltd | Construction | 2006 |
| Parekh Ventures Ltd | Construction | 1997 |