| O'Keefe Professional Services Limited | Professional & scientific | 2011 |
| Oakfield Management (GT B) Ltd | Households | 2017 |
| Oakgrove (Holly House) Management Company Limited | Real estate | 2015 |
| Object Oriented Hardware Limited | Professional & scientific | 1994 |
| Ocean Crossing Ltd | Health & social care | 2007 |
| Office Incorporated Limited | Construction | 2006 |
| Offley Chase Estates Limited | Real estate | 1989 |
| Offley New Homes Ltd | Real estate | 2024 |
| OH SO Glitter Limited | Manufacturing | 2017 |
| Old Bank House Dental Surgery Limited | Health & social care | 2007 |
| Old North Road Limited | Households | 1992 |
| Oluonye Ngozi Limited | Health & social care | 2026 |
| Ommadorn Limited | | 1983 |
| Omniscient Solutions Limited | Information & communication | 2002 |
| ON2U Promotions Limited | Administrative & support | 2003 |
| One Call Hire Limited | Administrative & support | 2016 |
| Oniva Limited | Professional & scientific | 2003 |
| Onli Properties Limited | Real estate | 2006 |
| Opel Estates Limited | Real estate | 2003 |
| Open Here Limited | Information & communication | 2007 |
| Optikinetics Limited | Manufacturing | 1970 |
| Optix Fire and Security 24/7 Limited | Professional & scientific | 2005 |
| Optvisual Computers Limited | Real estate | 1996 |
| Orlin Technologies Limited | Wholesale & retail | 2006 |
| P D Plastering Limited | Construction | 2001 |
| P L General Building Contractors Limited | Extraterritorial | 2001 |
| P S Process Improvement Limited | Professional & scientific | 2001 |
| P S Sidhu Limited | Financial services | 2015 |
| Palmbrook Properties Limited | Construction | 2020 |
| Panasshh Ltd | Professional & scientific | 2022 |
| Paragon Training (UK) Limited | Wholesale & retail | 2005 |
| Parallel Worlds (Books) Limited | Wholesale & retail | 2000 |
| Parkinson Cowan Limited | Professional & scientific | 1900 |
| Partners of Milton Keynes Limited | Professional & scientific | 1985 |
| Pathfinder Vehicle Systems Limited | Information & communication | 2006 |
| Paul Stephen Barbering Limited | Other services | 2007 |
| Paul Sweeney Limited | Construction | 2007 |
| PCL Corporatewear Limited | Wholesale & retail | 1994 |
| Peace Dragon Records Ltd. | Information & communication | 2020 |
| Peek Developments Limited | Real estate | 2004 |
| Pegasus Professional Services Limited | Professional & scientific | 2002 |
| Pelican Medics Ltd | Health & social care | 2024 |
| Pendulum Productions Ltd | Information & communication | 2023 |
| Peter Evans Studios Limited | Arts & recreation | 1976 |
| Peter Webster Music Limited | Information & communication | 2001 |
| Phaselarge Limited | Real estate | 1990 |
| Phelans Jewellers Limited | Wholesale & retail | 2006 |
| Phil Goodson Brickwork Contractors Limited | Construction | 1996 |
| Phil Jones Consultancy Limited | Professional & scientific | 2003 |
| Phoenix Optics (UK) Limited | Other services | 2003 |
| Photolit Printing Limited | Manufacturing | 1983 |
| Photoquest Ltd | Professional & scientific | 2006 |
| Pintea ENG Ltd | Construction | 2016 |
| Pitamber Limited | Real estate | 2005 |
| PKW Accountancy Limited | Professional & scientific | 2004 |
| Placing People (Bedford) Limited | Administrative & support | 2005 |
| Platina Limited | Information & communication | 1996 |
| Playturf Limited | Construction | 2008 |
| PO Shin TAO TEH Association Limited | Other services | 1989 |
| Polar Speed Distribution Limited | Transport & logistics | 1996 |
| Poplar Homes Limited | Real estate | 2002 |
| Poppy Gardens MGT Co Ltd | Households | 2022 |
| POR Ultimo Ltd | Information & communication | 2021 |
| Portasa Limited | Professional & scientific | 2004 |
| Porthmeor Investments Limited | Real estate | 2007 |
| Portland Industrial Estate Management Limited | Real estate | 1970 |
| Positive Software Productions Ltd | Information & communication | 1999 |
| PPS Investments Limited | Professional & scientific | 2003 |
| Praiseposter Limited | Real estate | 2001 |
| Praxissolutions Limited | Information & communication | 2006 |
| Precraft Limited | | 1986 |
| Prestwood Carpets | | 1990 |
| PRG Carpentry Limited | Construction | 2003 |
| Priory Construction (Eastern) Limited | Professional & scientific | 2003 |
| Professional Pest Management Limited | Administrative & support | 2003 |
| Protronix EMS Limited | Manufacturing | 2006 |
| Proving Services Limited | Information & communication | 2001 |
| Puckeridge Management Co Ltd | Real estate | 2023 |
| Pulp Theatre Limited | Information & communication | 2000 |
| Purdue Metals Limited | Real estate | 1958 |
| PWT Property Group Ltd | Real estate | 2024 |
| Q B a S Limited | Professional & scientific | 2003 |
| Quattro Engineering Limited | | 1985 |
| Quick Essential Trans Limited | Transport & logistics | 2007 |
| Quince Stoneworks Limited | Construction | 2005 |
| R & J Hardware Limited | Wholesale & retail | 2002 |
| R a D Associates Limited | Information & communication | 1994 |
| R G Grant & Sons Ltd | Transport & logistics | 2001 |
| R.A. Gibson (Colesden) Limited | Agriculture & fishing | 1945 |
| R.B.F. Limited | Real estate | 2002 |
| R.J.W. Autos Limited | Wholesale & retail | 2003 |
| R.P. Testa Plumbing and Heating Services Limited | Construction | 2003 |
| Rahbar Trust | Education | 1999 |
| Raidxtreme (UK) Limited | Arts & recreation | 2007 |
| Raptr Martial Arts Ltd | Arts & recreation | 2020 |
| Rareunit Limited | Transport & logistics | 1997 |
| Rawlinson Pryde Limited | Professional & scientific | 2002 |
| RAY Sarll Renovations Limited | Construction | 2007 |
| RCH London Ltd | Professional & scientific | 2019 |
| Ready Reckoners Limited | Professional & scientific | 2003 |