| Mayflower Health and Beauty Clinic Limited | Other services | 2003 |
| MBL Media Ltd | Other services | 2007 |
| Mccormick (UK) Pension Scheme Trustees Limited | Professional & scientific | 2025 |
| Mccormick Emea Holdings Limited | Financial services | 2022 |
| Mckenzie Mills Partnership Limited | Information & communication | 2007 |
| Media Friendly Training Limited | Extraterritorial | 1998 |
| Mega-Pak Limited | Wholesale & retail | 1991 |
| Meggas Ltd | Transport & logistics | 2024 |
| Melbourne (Dover) Management Company Limited | Households | 1988 |
| Meowve - Three Counties Ltd | Professional & scientific | 2026 |
| Merkko Builders Merchants (Oxford) Ltd | Wholesale & retail | 2006 |
| Merkko Builders Merchants (Reading) Ltd | Wholesale & retail | 2013 |
| Merkko Group Ltd | Professional & scientific | 2015 |
| Merkko LED Lighting Ltd | Wholesale & retail | 2015 |
| Merrigate Limited | Wholesale & retail | 2004 |
| Michael J Emery & Co Limited | Professional & scientific | 2007 |
| Mike Birkhead Associates Limited | Information & communication | 2006 |
| Mike Walsh Engineering Limited | Professional & scientific | 1995 |
| Milburn Productions Limited | Real estate | 1973 |
| Miles Shepherd Limited | Administrative & support | 2003 |
| Milton Keynes Water Softeners Ltd | Water & waste | 2000 |
| Mindlink Consultancy Limited | Information & communication | 1995 |
| Mini-Plastics Limited | Wholesale & retail | 1994 |
| Mirror 2 Mirror Ltd | Manufacturing | 2003 |
| Miss SOY Ltd. | Wholesale & retail | 2005 |
| Mission Possible=Life Limited | Other services | 2025 |
| Mitchell and Co Building & Renovation Ltd | Construction | 1996 |
| Mitore Solutions Limited | Administrative & support | 2005 |
| MK Gallery | Arts & recreation | 1989 |
| MK T&B Centre Limited | Wholesale & retail | 2003 |
| MMC Aircraft Limited | Transport & logistics | 2006 |
| Mobar Systems Ltd | Information & communication | 2005 |
| Model Minds Ltd | Education | 2006 |
| Monks Hollow Ventures Limited | Extraterritorial | 2004 |
| Moonglow Property Management Limited | Households | 1982 |
| Morgan Stearns Limited | Professional & scientific | 2005 |
| Mosaic Fusions Ltd | Professional & scientific | 2001 |
| Motion Asset Group Ltd | Arts & recreation | 2025 |
| Mountainloom Studio Ltd | Wholesale & retail | 2025 |
| Moxby Computers Limited | Information & communication | 1997 |
| Mprd Limited | Manufacturing | 2017 |
| Mulhall and Co Limited | Professional & scientific | 2003 |
| Muswell Hill Investments Limited | Real estate | 1964 |
| Mwfmt Limited | Education | 2002 |
| My Clockwork IT Ltd | Information & communication | 2011 |
| Naaseda Limited | Real estate | 2024 |
| NAS TEK Limited | Information & communication | 1998 |
| Nashleigh Hill Management Company Limited | Real estate | 2005 |
| Nature Wide Landscaping Paving Limited | Administrative & support | 2025 |
| Neesham Public Relations Limited | Professional & scientific | 1999 |
| Netherwood Autos Limited | Wholesale & retail | 1991 |
| Never Again Productions Limited | Information & communication | 2003 |
| New Beginnings Day Nursery Limited | Health & social care | 2004 |
| New Kinetics Limited | Information & communication | 2000 |
| New Life Residential Limited | Hospitality | 2020 |
| New Young's (Wycombe) Ltd | Hospitality | 2017 |
| News Media Channel Ltd | Information & communication | 2025 |
| Nexgas Limited | Mining & quarrying | 2003 |
| Nicel Precision Engineering Limited | Professional & scientific | 1999 |
| Nightingale Jewellers Limited | Wholesale & retail | 2001 |
| Nikad Electronics Limited | Wholesale & retail | 2002 |
| Nilex Consultancy Services Limited | Professional & scientific | 1998 |
| NMC Sportif Limited | Wholesale & retail | 1993 |
| No-Frills Retail Ltd | Wholesale & retail | 2021 |
| Normandy House Limited | Professional & scientific | 2003 |
| Northcliff Limited | Real estate | 1986 |
| Noventum Service Management Consultants Limited | Professional & scientific | 2008 |
| Noventum SMC Limited | Financial services | 2008 |
| Novotech Services Limited | Information & communication | 1996 |
| Novus Property Development Limited | Construction | 2007 |
| Nylon Colours Limited | Manufacturing | 1999 |
| O'Mahony Contractors Limited | Construction | 2000 |
| Oak Aston Limited | Information & communication | 2005 |
| Oakleaf Farm Trustees Ltd | Professional & scientific | 2025 |
| Oakridge Place Management Company Ltd | Households | 2002 |
| Oaks Community Church | Other services | 2002 |
| Old Court Flats Limited | Real estate | 2026 |
| Oldfield Music Limited | Arts & recreation | 1975 |
| Oldfield Music Overseas Limited | Arts & recreation | 1983 |
| Olney Landscapes Limited | Administrative & support | 2006 |
| Omnibridge Limited | Information & communication | 2002 |
| Omnispace Estates Ltd | Real estate | 2025 |
| One Stop Events Limited | Administrative & support | 2007 |
| Onlight Limited | Wholesale & retail | 2001 |
| Open University Worldwide Limited | Education | 1976 |
| Opio Limited | Real estate | 2007 |
| Orbital Electrical Limited | Construction | 2003 |
| Orbitdash Limited | | 1986 |
| ORP Investment (UK Omrf) LLP | | 2020 |
| Outlook on Life Ltd | Real estate | 2025 |
| Ovigal Limited | Professional & scientific | 2003 |
| Owen SPV Ltd | Real estate | 2020 |
| P L V Enterprises Limited | Hospitality | 1995 |
| P.M. Design Ltd | Information & communication | 2001 |
| P.T.E. Development Limited | Information & communication | 1998 |
| PAB (MK) Ltd | Professional & scientific | 2007 |
| Pageset Limited | Information & communication | 2002 |
| Paint-Ability Limited | Construction | 2006 |
| Paje Steel Products Limited | Real estate | 1978 |
| Palmac Electrical Services Limited | Construction | 1993 |