| Mark Ryan Limited | Information & communication | 2001 |
| Martin King Construction Limited | Construction | 2003 |
| Martins of Rushden Limited | Agriculture & fishing | 2004 |
| Matt Howell Photography Ltd | Professional & scientific | 2003 |
| MBG Solutions Limited | Professional & scientific | 2005 |
| MC Machinery Limited | Manufacturing | 2006 |
| Mclay-James Limited | Financial services | 2004 |
| Menu Innovators Limited | Professional & scientific | 2025 |
| Mercedes-Benz Grand Prix Estates Limited | Real estate | 2022 |
| Merland Copy Shop Limited | Wholesale & retail | 2006 |
| MIB-U2 Solutions Limited | Information & communication | 2004 |
| Michael Pawluk Architectural Services Limited | Professional & scientific | 2004 |
| Midland JAY Limited | Extraterritorial | 2006 |
| Mike Wells Cars Ltd | Wholesale & retail | 2007 |
| MJF Consultants Limited | Information & communication | 1993 |
| Mockett & Childs LLP | | 2026 |
| Monoworld Polymers Ltd | Water & waste | 2020 |
| Montague Jeffery Limited | Wholesale & retail | 2003 |
| Morgan Trice Consulting Ltd | Real estate | 2013 |
| MPC Plumbing & Heating Limited | Manufacturing | 2007 |
| MPG Professional Limited | Professional & scientific | 2006 |
| MRM Pharmacist Ltd | Wholesale & retail | 2022 |
| MST Construction Limited | Construction | 2005 |
| Mudworks Limited | Administrative & support | 2010 |
| MW Corporate Secretaries Limited | Professional & scientific | 2006 |
| N B Contractors Ltd | Wholesale & retail | 2005 |
| N.K.A. Hallin | Health & social care | 2007 |
| Nesbitt Training Limited | Education | 2003 |
| New Lodge Vineyard Limited | Agriculture & fishing | 2006 |
| New Provincial Enterprises Limited | Financial services | 1945 |
| New Yorker Barbers Limited | Other services | 2017 |
| Newton Textiles Limited | Wholesale & retail | 2004 |
| Nicholas and Steele Ltd | Wholesale & retail | 2010 |
| NN8 Group Ltd | Financial services | 2024 |
| Nola Limited | Administrative & support | 1974 |
| Norman Spence Decorators Ltd | Construction | 2003 |
| Norris Way Management Company Limited | Administrative & support | 2004 |
| North by Northwest Transport Services Limited | Transport & logistics | 2004 |
| Northampton Footwear Distributors Limited | Real estate | 1965 |
| Northampton Locksmiths Limited | Wholesale & retail | 1985 |
| Northampton Town FC Community Trust | Arts & recreation | 2001 |
| Northamptonshire Trampoline Gymnastics Academy Limited | Health & social care | 2005 |
| Northants Electrical Installations Limited | Construction | 2007 |
| Northants Specsavers Limited | Wholesale & retail | 1995 |
| Northants Visionplus Limited | Wholesale & retail | 2000 |
| NSL Systems Ltd | Information & communication | 1998 |
| Numbers Express Limited | Professional & scientific | 2003 |
| O'Brien Consulting Ltd. | Information & communication | 1999 |
| Oakley Plumbing Supplies Limited | Wholesale & retail | 2002 |
| Oasys P.C. Systems Limited | Information & communication | 2002 |
| Objective Travel Safety Limited | Administrative & support | 2004 |
| Ocarina Workshop Limited | Wholesale & retail | 1998 |
| Ocarina Workshop Publications Limited | Professional & scientific | 1998 |
| Ocarinas Direct Limited | Professional & scientific | 1998 |
| Occultique Limited | Wholesale & retail | 2001 |
| Okay Engineering Limited | Manufacturing | 2021 |
| Okay Rentals Limited | Administrative & support | 2021 |
| ON TAP Watercoolers Limited | Wholesale & retail | 2004 |
| ON Wheels Limited | Wholesale & retail | 2001 |
| Open Source Consultancy Ltd | Information & communication | 2002 |
| Operacy Limited | Professional & scientific | 2002 |
| Orchardlettings.Com Limited | Extraterritorial | 2000 |
| Ovaltech Business Solutions Limited | Professional & scientific | 1998 |
| Overstone Developments Limited | Extraterritorial | 1984 |
| P Bamsey Limited | Construction | 2006 |
| P S B Consultancy & Design Ltd | Professional & scientific | 2007 |
| P. J. Miller Limited | Manufacturing | 2003 |
| P. R. Soft Limited | Manufacturing | 1995 |
| Palletroute Limited | Transport & logistics | 1997 |
| Panache Pools Limited | Administrative & support | 2006 |
| Panda Cleaning Machines Limited | Wholesale & retail | 2002 |
| Paradise Computing Limited | Information & communication | 1987 |
| Parish Agencies Limited | Wholesale & retail | 2004 |
| Park View Ventures Ltd | Administrative & support | 2006 |
| Parker Structural Steelwork Limited | Construction | 2006 |
| Paul a Lewis Limited | Administrative & support | 2003 |
| Paul Grayson Rugby Ltd | Other services | 2003 |
| Paul Villiers (Floor Screeding) Limited | Construction | 2002 |
| PBR Limited | Real estate | 1966 |
| PCM Group UK Limited | Manufacturing | 1985 |
| Pcrg Limited | Professional & scientific | 2006 |
| Pentecostal Sanctuary Bible Ministries Limited | Other services | 2004 |
| Perky Properties Ltd | Real estate | 2019 |
| Pet Connect Uk-Eu Ltd | Transport & logistics | 2026 |
| Phoenix Furniture (Kettering) Ltd. | Water & waste | 2005 |
| Phoenix Personnel Limited | Administrative & support | 2005 |
| Photobrick (UKA) Ltd | Wholesale & retail | 2023 |
| Pilate's Face and Body Limited | Other services | 2006 |
| PJM Roofing Limited | Construction | 2002 |
| Planet Supplies Limited | Wholesale & retail | 2001 |
| PLANNING4LIFE LLP | | 2003 |
| Playground Supplies Limited | Construction | 1997 |
| Polylogic Limited | Information & communication | 2002 |
| Poplar Cleaning Services Ltd | Administrative & support | 2006 |
| Porobic Associates Limited | Professional & scientific | 1998 |
| Precision Surveys Limited | Construction | 2004 |
| Premium IT Ltd | Information & communication | 2007 |
| Preppie Limited | Wholesale & retail | 2003 |
| Prime Choice Limited | Real estate | 1992 |
| Primeland Developments Limited | Real estate | 1997 |