| Manor Body Repairs Limited | Wholesale & retail | 2003 |
| Manor Car Storage Limited | Transport & logistics | 2013 |
| Manor Farms Barley LP | | 2010 |
| Manor Organics Ltd | Agriculture & fishing | 2020 |
| Mantles Group (Properties) Limited | Real estate | 2020 |
| Mantles Group (Trading) Limited | Financial services | 2020 |
| Mantles Group Limited | Wholesale & retail | 1938 |
| Maple Joinery Cambridge Limited | Manufacturing | 2003 |
| Marchant IT Solutions (Mitsol) Limited | Information & communication | 2005 |
| Marchnata Group Ltd | Professional & scientific | 2024 |
| Marcin Owczarski Ltd | Transport & logistics | 2022 |
| Mardles Life Limited | Information & communication | 2026 |
| Mardon Estates Limited | Financial services | 1945 |
| Mareway Information Management Services Ltd | Information & communication | 2017 |
| Maria Shaughnessy Fractional Services Ltd | Administrative & support | 2025 |
| Mark Blundell Ltd | Wholesale & retail | 2017 |
| Mark Brazier-Jones Limited | Arts & recreation | 2003 |
| Mark Weatherhead Limited | Agriculture & fishing | 1981 |
| Mark Winter Property Developers Limited | Construction | 2001 |
| Market One Trading (UK) Ltd | Wholesale & retail | 2011 |
| Marketing Minders Limited | Professional & scientific | 2011 |
| Marketing Quality Assurance Limited | Professional & scientific | 1992 |
| Marlie Builders Limited | Construction | 2020 |
| Maros Lettings Ltd | Real estate | 2025 |
| Mart Barrass Architect Ltd | Professional & scientific | 2011 |
| Martin Caunt Agencies Limited | Wholesale & retail | 2013 |
| Martin Raymond Limited | Professional & scientific | 2022 |
| Martyn Downer Works of Art Limited | Professional & scientific | 2014 |
| Marvall Services Limited | Administrative & support | 2013 |
| Mary Wear Limited | Professional & scientific | 2011 |
| Matera Eco Ltd | Information & communication | 2026 |
| Matt P James Carpentry Services Limited | Construction | 2022 |
| Matthew Paterson Agronomy Limited | Professional & scientific | 2011 |
| MAY Agrifood Services Limited | Professional & scientific | 2017 |
| Maybrey Precision Castings Limited | Manufacturing | 2001 |
| Mays Groundworks Limited | Construction | 2018 |
| Maytum & Clark Lifestyle Limited | Other services | 2019 |
| MC Performance Ltd | Arts & recreation | 2021 |
| Mccarthy Holdings Group Ltd | Wholesale & retail | 2021 |
| Mcginley Performing Arts Limited | Education | 2013 |
| Mcginty and Sons Investments Ltd | Financial services | 2021 |
| Mcguffin Brothers Limited | Information & communication | 2008 |
| MCI Precision Screens Limited | Manufacturing | 2009 |
| MD Care Homes Limited | Health & social care | 2017 |
| MDS Consulting Group Ltd | Professional & scientific | 2025 |
| Meadview Services Limited | Administrative & support | 2025 |
| Media Matters Group Limited | Extraterritorial | 2022 |
| Medicines and Medical Devices Network Africa (Mmedna) Ltd | Administrative & support | 2024 |
| Medieval Jack Limited | Wholesale & retail | 2023 |
| Melbourn Auto Services Ltd | Wholesale & retail | 2020 |
| Melbourn Aviation Consultancy Limited | Professional & scientific | 2020 |
| Melbourn Buildings & Fencing Supplies Limited | Wholesale & retail | 2003 |
| Melbourn Car Body Work Ltd | Wholesale & retail | 2025 |
| Melbourn Chip Shop Ltd | Hospitality | 2025 |
| Melbourn Community Hub Management Group | Hospitality | 2012 |
| Melbourn Flooring & Interiors Limited | Wholesale & retail | 2003 |
| Melbourn Scientific Limited | Professional & scientific | 1989 |
| Melde's Keep (Melbourn) Management Company Limited | Real estate | 2016 |
| Meldform Processing Limited | Manufacturing | 1981 |
| Meldreth Landscapes Limited | Administrative & support | 2001 |
| Meldreth Manor Limited Partnership | | 2007 |
| Meldreth Motor Company (Services) Ltd | Wholesale & retail | 2002 |
| Meldrum Group Ltd | Financial services | 2018 |
| Memo Press Limited | Manufacturing | 2021 |
| Meraki Renovations Ltd | Construction | 2021 |
| Mere Advice Limited | Professional & scientific | 2012 |
| Merivel Capital Partners LLP | | 2023 |
| Merivel Limited | Professional & scientific | 2018 |
| Meshcom UK Limited | Manufacturing | 2009 |
| Metal Mate (Biggleswade) Limited | Manufacturing | 1989 |
| Mettler-Toledo Safeline X-Ray Limited | Manufacturing | 2000 |
| Mfbg Ltd | Professional & scientific | 2013 |
| Mia's Home Ltd | Wholesale & retail | 2019 |
| Mialsha Ltd | Wholesale & retail | 2026 |
| Michael Willis Design Ltd | Administrative & support | 2017 |
| Micron Bio-Systems Ltd | Manufacturing | 1997 |
| Milk ZIP Ltd | Professional & scientific | 2024 |
| Mill Courtyard (Steeple Morden) Management Company Limited | Real estate | 2021 |
| Mill END Farms Limited | Agriculture & fishing | 1961 |
| Mill Studio Business Centre Limited | Construction | 1989 |
| Mill Studio Holdings Limited | Professional & scientific | 1987 |
| Milldyke Gardens Limited | Administrative & support | 2005 |
| Millframe Fine Arts Limited | Wholesale & retail | 1993 |
| Mills Editing Limited | Information & communication | 2014 |
| Minders Keepers Limited | Other services | 1994 |
| Mini Ballers Basketball Limited | Arts & recreation | 2024 |
| Mini Glam Ltd | Wholesale & retail | 2026 |
| Minicome Limited | Households | 1981 |
| Ministore Limited | Transport & logistics | 2016 |
| Minotaur Inc. Limited | Administrative & support | 2012 |
| Mion Studio Ltd | Professional & scientific | 2022 |
| Mismarthome Ltd | Information & communication | 2025 |
| Miyabi Property Maintenance Limited | Real estate | 2025 |
| MJ Hunt Ltd | Hospitality | 2016 |
| MJL Developments Limited | Construction | 1970 |
| MJM Abacus Ltd | Administrative & support | 2022 |
| MK Official Catering Limited | Hospitality | 2025 |
| MK Plumbing and Drainage Ltd | Construction | 2016 |
| MK X Limited | Professional & scientific | 1999 |
| MMM Proper Tea Limited | Real estate | 2019 |