| M.J.Tree Services Limited | Agriculture & fishing | 2004 |
| Mablex Engineering Limited | Manufacturing | 2007 |
| Mackinnon Construction Limited | Construction | 1999 |
| Macrae Farms Limited | Agriculture & fishing | 1957 |
| Made Purple Investments Limited | Real estate | 2020 |
| Made Purple Ltd | Information & communication | 2018 |
| Magic Online Solutions Limited | Information & communication | 2006 |
| Mainline Internet Services Limited | Information & communication | 1999 |
| Majestic Pools Limited | Construction | 2002 |
| Major Demolition Limited | Construction | 1996 |
| Majorettes (Norwich) Limited | Transport & logistics | 1954 |
| Maltings Close Residents Association (Halesworth) Limited | Real estate | 1977 |
| Maneline Coachworks Limited | Manufacturing | 2003 |
| Manwaring Professional Services Limited | Other services | 2006 |
| Mapus-Smith & Lemmon LLP | | 2007 |
| Marine Weld Fabrication Limited | Manufacturing | 2004 |
| Mark Vigrass Limited | Administrative & support | 2003 |
| Mark Welch Building Services Limited | Construction | 2015 |
| Mark Welch Properties Limited | Real estate | 2025 |
| Martin Sexton Prints & Cards Limited | Information & communication | 2002 |
| Martins Plastics Limited | Wholesale & retail | 1976 |
| Masson Seeley and Company,Limited | Manufacturing | 1920 |
| Mats Express Ltd | Professional & scientific | 2025 |
| Matthews Builders Limited | Construction | 2003 |
| Mayuda Limited | Professional & scientific | 2006 |
| MC Lead Glaziers Limited | Construction | 2003 |
| MCB FS Consulting Limited | Professional & scientific | 2025 |
| Mcdaniel's Limited | Education | 2001 |
| MD ARB Ltd | Professional & scientific | 2023 |
| Mead Contractors Limited | Construction | 2021 |
| MEG Builders Limited | | 1985 |
| Mejo Design Ltd | Real estate | 2007 |
| MEL Carter Groundworks Limited | Construction | 2007 |
| Melbourne Mews Management Limited | Real estate | 1990 |
| Menutex Limited | Professional & scientific | 1998 |
| Merlin Translations Limited | Professional & scientific | 2018 |
| MFF Delivery Ltd | Administrative & support | 2017 |
| Michael Baker Building Maintenance Limited | Construction | 2003 |
| Mick Peake Motors Limited | Wholesale & retail | 2003 |
| Micon International Co Limited | Administrative & support | 2000 |
| Middletons (Chelmsford) Limited | Hospitality | 2025 |
| Middletons (Colchester) Limited | Hospitality | 2025 |
| Middletons (KL) Limited | Hospitality | 2025 |
| Middletons (Leicester) Limited | Hospitality | 2025 |
| Middletons (Norwich) Limited | Hospitality | 2025 |
| Middletons (Peterborough) Limited | Hospitality | 2025 |
| Middletons (Wymondham) Limited | Wholesale & retail | 1999 |
| MIG Anglia Limited | Manufacturing | 1987 |
| Miguel Bestard Carpentry Limited | Construction | 2007 |
| Milligan Hotel & Restaurant Company Limited | Hospitality | 2007 |
| Mills & Malucelli Limited | Wholesale & retail | 2005 |
| Mills Brothers Builders Limited | Construction | 2003 |
| Mirage Haulage Limited | | 1991 |
| Mitchell Demolition Limited | Construction | 2005 |
| Mizsei Ward Consultancy Limited | Information & communication | 2007 |
| MJB Consultancy (East) Limited | Professional & scientific | 2023 |
| Mjkm Services Limited | Construction | 2003 |
| MKN UK Limited | Extraterritorial | 2007 |
| ML Garage Limited | Wholesale & retail | 2015 |
| Modelling Hairstyles Ltd | Other services | 2007 |
| Moneyfacts Group Holdings Limited | Information & communication | 2007 |
| Moneyfacts Limited | Extraterritorial | 1988 |
| Moor Farm Meats Ltd | Wholesale & retail | 2019 |
| Mooroolbark Rossie Braes Limited | | 1986 |
| Morina Property Investments Ltd | Real estate | 2025 |
| Morris Armitage Dmkt Limited | Real estate | 2006 |
| Morrissey Builders Limited | Construction | 2005 |
| Morton & Page Farm & Garden Supplies Limited | | 1977 |
| Morton Enterprises Limited | Wholesale & retail | 1940 |
| Motosave Limited | Wholesale & retail | 1980 |
| Mowzer Motorsport Limited | Manufacturing | 2004 |
| MR. Plastic Limited | Wholesale & retail | 1996 |
| MRL Systems Limited | Manufacturing | 1999 |
| MS Marketing Services Limited | Wholesale & retail | 2005 |
| MTE Autos Ltd | Wholesale & retail | 2022 |
| Mulberry Tree Homes Limited | Construction | 2007 |
| Mundesley Volunteer Inshore Lifeboat Limited | Other services | 1973 |
| Mussett Helicopters Limited | Information & communication | 1990 |
| Myriad Investments (UK) Limited | Real estate | 2004 |
| N a C Cafe Bar Limited | Hospitality | 1999 |
| N Kelly Ltd | Construction | 2015 |
| N. G. Dawson Accountancy Services Limited | Professional & scientific | 2006 |
| N.L.Roper & Sons Limited | Manufacturing | 1972 |
| Naked Manufacturing Group Holdings Limited | Wholesale & retail | 2006 |
| Nanoflam Holdings Limited | Financial services | 2017 |
| Narstate Limited | Agriculture & fishing | 1979 |
| Nart Retail Ltd | Wholesale & retail | 2017 |
| Natrimi Ltd | Other services | 2021 |
| Nawzad Holdings Limited | Financial services | 2023 |
| Ncnuk CIC | Other services | 2025 |
| Necton Farms Limited | Agriculture & fishing | 1953 |
| Neil Whicker Electrical Services Limited | Construction | 2005 |
| Nelstar Limited | Extraterritorial | 1980 |
| Nemsdune Limited | | 1976 |
| NET Paragon Solutions Limited | Information & communication | 2000 |
| Neurokin Network Ltd | Professional & scientific | 2024 |
| Neville Godfrey Limited | Construction | 2008 |
| New Fortune Ltd | Hospitality | 2024 |
| New WOK Well Limited | Hospitality | 2020 |
| Newfoundlands Limited | Water & waste | 2004 |