| Malcuth Ltd. | Real estate | 2022 |
| Mamada Ltd | Real estate | 2022 |
| Manchester Mercantile Ltd | Wholesale & retail | 2023 |
| Mango Code Limited | Information & communication | 2018 |
| Marasao (UK) Limited | Professional & scientific | 2024 |
| Marc Leather Limited | Wholesale & retail | 2024 |
| Marco Ruffatti Ltd | Wholesale & retail | 2014 |
| Maria Jones Clinical Psychology Services Ltd | Health & social care | 2015 |
| Marianne Olyver and HER Orchestra Limited | Arts & recreation | 1998 |
| Marianpruitt Ltd | Wholesale & retail | 2025 |
| Marisand Properties Limited | Real estate | 2007 |
| Maritime Consulting Associates Limited | Professional & scientific | 1981 |
| Mark Alderton Holdings Limited | Real estate | 1987 |
| Mark Bouttell Electrical Services Limited | Construction | 2003 |
| Mark Ferrari Limited | Wholesale & retail | 1995 |
| Mark Hall Electrical Installations Limited | Construction | 2003 |
| Mark Kennedy (Lowestoft) Limited | Construction | 2005 |
| Mark Swift Design Ltd | Professional & scientific | 2008 |
| Marketzen Limited | Administrative & support | 2025 |
| Marleys Confectionery Limited | Wholesale & retail | 2018 |
| Martin Emmanuel Ltd | Information & communication | 2021 |
| Martin Melville Plumbing & Heating Limited | Construction | 2001 |
| Martin Troughton Consulting Ltd | Professional & scientific | 2022 |
| Martlesham Heath Squash Club Limited | Arts & recreation | 1976 |
| Mastrends Ltd | Wholesale & retail | 2023 |
| Matthew Kibble Transport Limited | Transport & logistics | 2001 |
| Maxwell Hairdressing Limited | Other services | 2002 |
| Maxxis International (UK) Ltd | Wholesale & retail | 1975 |
| Mazzam Limited | Wholesale & retail | 2020 |
| MB Film & TV Construction Limited | Construction | 2002 |
| Mbli Ltd | Manufacturing | 2023 |
| MBR Technologies Ltd | Manufacturing | 2025 |
| Mdstg Limited | Wholesale & retail | 2021 |
| Meare Landscaping Limited | Construction | 2007 |
| Medical Device Technology Consultants Limited | Health & social care | 2004 |
| Medimap Limited | Professional & scientific | 2005 |
| Melford Green Limited | Extraterritorial | 2005 |
| Melly Store Ltd | Wholesale & retail | 2024 |
| Melton Boatyard Limited | Manufacturing | 1981 |
| Messrs P J and M W Richards | | 1995 |
| Messrs. H. & V. Horsley | | 1992 |
| Messrs. John Brown & Sons | | 1993 |
| Metal Office Equipment Limited | Manufacturing | 1987 |
| Method ERP Ltd | Professional & scientific | 2017 |
| Metisra Consulting Limited | Professional & scientific | 2018 |
| MGO Marketing Limited | Wholesale & retail | 2023 |
| MHW Ventures Limited | Real estate | 2024 |
| Michael Page Services Limited | Construction | 2003 |
| Micro Filtration Limited | | 1982 |
| MID Anglian Enterprise Agency Limited | Administrative & support | 1984 |
| MID Suffolk Citizens Advice Bureau | Information & communication | 2004 |
| MID Suffolk Fencing Limited | Construction | 1999 |
| MID Suffolk Voluntary Organisations Forum | Other services | 1998 |
| Mihai Preda Transport Ltd | Administrative & support | 2018 |
| Mike Herbert Limited | Administrative & support | 2003 |
| Milas Global Ltd | Wholesale & retail | 2024 |
| Mildenhall Auto Centre Limited | Wholesale & retail | 1982 |
| Mildenhall Tyre & Auto Centre Ltd | Manufacturing | 2003 |
| Miles Developments Limited | Real estate | 2007 |
| Minutaie Ltd | Wholesale & retail | 2024 |
| Miracle Mills Limited | Extraterritorial | 1985 |
| Mishibell Limited | Wholesale & retail | 2024 |
| Misty Rain Limited | Information & communication | 2025 |
| Mitchell's Garage (Lowestoft) Limited | Wholesale & retail | 1975 |
| Mitchell's Motor Repairs Limited | Wholesale & retail | 2000 |
| MKT Logistics Limited | Transport & logistics | 2008 |
| MKU Properties Limited | Real estate | 2026 |
| MLT Transport Ltd | Transport & logistics | 1995 |
| MNN Consulting Limited | Administrative & support | 2023 |
| MNO Contracts Ltd | Construction | 2022 |
| Moddtech Media Limited | Information & communication | 2024 |
| Monarch Joinery Limited | Manufacturing | 1990 |
| Monastics Recruitment Ltd | Administrative & support | 2023 |
| Moneywealth Info Systems Limited | Wholesale & retail | 2023 |
| Mood and Space Ltd | Construction | 2022 |
| Moonrise.Mk Ltd | Wholesale & retail | 2024 |
| Moore Green Limited | Professional & scientific | 2001 |
| Moorst Ltd | Information & communication | 2023 |
| Moreside Investments Corporation Limited | Extraterritorial | 2002 |
| Morgan LE FAY Ltd | Manufacturing | 2024 |
| Mortimers Seafood Restaurant Limited | Real estate | 1985 |
| Motal & Moolchand Ltd | Wholesale & retail | 2021 |
| Moulton Manor Farm | Agriculture & fishing | 1963 |
| Mount Lofty Ltd | Health & social care | 2025 |
| Mountain Aquatics Ltd | Administrative & support | 2023 |
| Mowbon Limited | Real estate | 2006 |
| MP Eastern Partners LLP | | 2018 |
| MRA Transport Ltd | Transport & logistics | 2006 |
| MRT Communications Limited | Professional & scientific | 1999 |
| MS7 Associates Ltd | Administrative & support | 2017 |
| Msne Property Investment Ltd | Real estate | 2025 |
| Multi Treasure Int’L Co., Ltd | Extraterritorial | 2015 |
| Muntons (Holdings) PLC | Professional & scientific | 1979 |
| Muntons PLC | Manufacturing | 1921 |
| Muntons Trustees Limited | Professional & scientific | 2002 |
| Mushkin Mallin Ltd | Wholesale & retail | 2022 |
| Music Box DJ Ltd | Arts & recreation | 2015 |
| Musicbank Records Limited | Professional & scientific | 2001 |
| MVP Engineering Limited | Manufacturing | 2006 |
| MX33 Group Commodities Ltd | Manufacturing | 2022 |