| Market Hill Ltd | Hospitality | 2019 |
| Markham Funeral Service Ltd | Other services | 2019 |
| Maro Entertainment Ltd | Information & communication | 2024 |
| Marriage Sofa Design Ltd | Manufacturing | 2008 |
| Marshall Electrical Ltd | Construction | 2015 |
| Marshall Hatchick LLP | | 2017 |
| Marshall Wolfe Limited | Professional & scientific | 2017 |
| Martlesham Body Repair Centre Limited | Manufacturing | 2023 |
| Martlesham Fencing Limited | Construction | 2022 |
| Martlesham New Homes Limited | Construction | 2014 |
| Martley Hall Stud Limited | Agriculture & fishing | 2020 |
| Marts INK Ltd | Professional & scientific | 2023 |
| Mary Merheim Ltd | Education | 2020 |
| Masseria UK Limited | Other services | 2022 |
| Masterplast Craftsmen Ltd | Construction | 2025 |
| Matheson Electrical Limited | Construction | 2021 |
| Matthew Scott Page Limited | Information & communication | 2021 |
| Maverick Festival Productions Ltd | Arts & recreation | 2011 |
| Mawburg Freehold Investments Ltd | Real estate | 2021 |
| Mawburg Limited | Professional & scientific | 2026 |
| MAX Ashken Limited | Administrative & support | 2026 |
| Mazzoni UK Limited | Real estate | 2008 |
| MB Planning Ltd | Professional & scientific | 2020 |
| Mbop.Dev Limited | Education | 2025 |
| MCG Land Limited | Households | 2019 |
| MD Academy of Languages Limited | Professional & scientific | 2024 |
| Meadows Agricultural Services Ltd | Agriculture & fishing | 2014 |
| Meare Castle Gundogs Ltd | Other services | 2026 |
| MEF Services Limited | Construction | 2008 |
| Megahart Developments Limited | Construction | 2014 |
| Meihua Limited | Professional & scientific | 2025 |
| Melbye Limited | Wholesale & retail | 2019 |
| Melectronics Systems Limited | Manufacturing | 2005 |
| Melford Peaks Ltd | Real estate | 2022 |
| Melissa Billen Designs Ltd | Construction | 2014 |
| Melons Green Ltd | Wholesale & retail | 2018 |
| Melton Day Nursery Limited | Education | 2008 |
| Melton Fish Bar Limited | Hospitality | 2007 |
| Melton Grange Apartments Management Limited | Households | 2012 |
| Melton Meat Products Limited | Wholesale & retail | 2007 |
| Melton Park Management Company Limited | Other services | 1998 |
| Melton Produce Limited | Wholesale & retail | 2020 |
| Melton Terrace Coppice Management Limited | Households | 2009 |
| Mend AI Ltd | Information & communication | 2025 |
| MEP Lettings Ltd | Real estate | 2020 |
| MEP Logic Ltd | Professional & scientific | 2018 |
| Merlin's Pets Ltd | Manufacturing | 2024 |
| Mesa Intelligence Limited | Information & communication | 2016 |
| Metalfix Limited | Manufacturing | 1992 |
| Metalfix Marine Limited | Manufacturing | 2001 |
| Methodology Limited | Professional & scientific | 2012 |
| MF Building Solutions Ltd | Construction | 2019 |
| MF Group Construction Ltd | Construction | 2021 |
| MGR Property Investments Limited | Construction | 2023 |
| MH Freight Specialists Limited | Professional & scientific | 2019 |
| MHB Prop Ltd | Real estate | 2025 |
| MHB Property Developments Ltd | Real estate | 2014 |
| MHC Consultancy Services Ltd | Professional & scientific | 2026 |
| Mia's Luxury Limited | Wholesale & retail | 2017 |
| MIC Animal Services Ltd | Professional & scientific | 2021 |
| Michael Howard Homes (Badley) Limited | Construction | 2018 |
| Michael Howard Homes 10 Limited | Construction | 2021 |
| Michael Howard Homes Limited | Construction | 2016 |
| Mifio Limited | Professional & scientific | 2026 |
| Mike Chittock Consulting Limited | Information & communication | 2007 |
| Mike Holmes AFA Limited | Professional & scientific | 2005 |
| Millermore Limited | Professional & scientific | 2018 |
| Milli’S Sewing Studio Limited | Manufacturing | 2021 |
| Millwest Estates & Investments Ltd | Financial services | 2012 |
| Milly Milly Limited | Extraterritorial | 2007 |
| Milton Keynes Surgery Centre Limited | Health & social care | 2019 |
| Mind Body and Sea CIC | Health & social care | 2024 |
| Mindwalks Limited | Professional & scientific | 2011 |
| Mini Motley Sanctuary CIC | Agriculture & fishing | 2026 |
| Minima Design Holdings Limited | Financial services | 2013 |
| Ministry of Caravans Limited | Information & communication | 2010 |
| Ministry of Motorhomes Limited | Information & communication | 2010 |
| Mint and Mustard Produce Ltd | Agriculture & fishing | 2016 |
| Mitchell Restoration Ltd | Construction | 2020 |
| MJC Carpentry & Construction Ltd | Construction | 2026 |
| MJU Woodbridge Ltd | Hospitality | 2022 |
| Moat Hall Farms Limited | Agriculture & fishing | 2013 |
| Moat Therapy Limited | Health & social care | 2022 |
| Mobile Checkup Ltd | Wholesale & retail | 2023 |
| Modern Classic Boats Ltd | Manufacturing | 2025 |
| Modular Consultants Ltd | Construction | 2020 |
| Montbards Group Ltd | Financial services | 2025 |
| Moon & Sixpence Limited | Hospitality | 1992 |
| Moons Beautique Ltd | Wholesale & retail | 2026 |
| Moore Bros Framlingham Ltd | Other services | 2023 |
| Moorgate IT Limited | Wholesale & retail | 2002 |
| More Metacognition Ltd | Education | 2021 |
| Morgan Beanstalk LLP | | 2022 |
| Morley Electrical (Suffolk) Ltd | Construction | 2016 |
| Mornington Consulting Limited | Information & communication | 1997 |
| Morrison and Sons Holdings Ltd | Financial services | 2024 |
| Mortgage NOW UK Limited | Financial services | 2003 |
| Mortlock Yachts Limited | Manufacturing | 2021 |
| Morton Wright Associates Ltd | Professional & scientific | 2015 |
| Mosstone Property Ltd | Real estate | 2025 |