| Malerassa Ltd | Agriculture & fishing | 2021 |
| Malleshwari&S Limited | Wholesale & retail | 2026 |
| Mally Consulting Ltd | Hospitality | 2007 |
| Mamma Mia's Chicken Limited | Hospitality | 2022 |
| Mander Pools Limited | Construction | 1994 |
| Manning Properties Ltd | Real estate | 2019 |
| Manor Lodges Murrow Limited | Real estate | 2017 |
| Manormade Limited | Hospitality | 2014 |
| MAR GAB Transport Ltd | Transport & logistics | 2021 |
| Marco Shop UK Ltd | Wholesale & retail | 2025 |
| Marcus Brown Plant Hire Ltd | Other services | 2017 |
| Mariflo Ltd | Other services | 2025 |
| Marika Page Fashion Stylist Limited | Professional & scientific | 2018 |
| Marina and Holiday Park Solutions Ltd | Construction | 2016 |
| Mark Patrick Limited | Administrative & support | 2003 |
| Mark Peeling Plastering Limited | Construction | 2011 |
| Markem Property Limited | Real estate | 2021 |
| Maro Consultancy Ltd | Agriculture & fishing | 2022 |
| Marshall Brooks Associates Limited | Professional & scientific | 2009 |
| Marshland Bulbs Ltd | Wholesale & retail | 2025 |
| Marshland Estates Limited | Real estate | 2019 |
| Martin & Sons (March) Limited | Agriculture & fishing | 1950 |
| Martin Paul Properties Ltd | Real estate | 2020 |
| Martin Works Limited | Manufacturing | 2019 |
| Martyn Kierman Plumbing & Heating Ltd | Construction | 2015 |
| Mast Haulage Limited | Transport & logistics | 2025 |
| Masterfilter Limited | Manufacturing | 2014 |
| Mastermind Supply Limited | Manufacturing | 2022 |
| Matchwell Developments Limited | Construction | 2024 |
| Matt Dawson Contracting Limited | Construction | 2026 |
| Matthew Crawford Construction Ltd | Construction | 2021 |
| Maurice Crouch (Growers) Limited | Agriculture & fishing | 1944 |
| Maurice Crouch (Holdings) Ltd | Financial services | 2020 |
| Maxey Grounds & Co LLP | | 2011 |
| Maxis Bars Limited | Hospitality | 2016 |
| Maxtreme Limited | Arts & recreation | 2006 |
| Mayfield Construction Ltd | Real estate | 2022 |
| MB Automobile Ltd | Wholesale & retail | 2021 |
| MB Walnut Steel Ltd | Manufacturing | 2020 |
| MC Travel Services Ltd | Transport & logistics | 2019 |
| Mcgreevy Management Ltd | Professional & scientific | 2026 |
| MCJ Lemagnen Associates Ltd | Professional & scientific | 2009 |
| MCK Build Ltd | Construction | 2016 |
| MCK Estates Ltd | Real estate | 2024 |
| Mclatchie Properties Limited | Real estate | 2020 |
| MCN (Distribution) Ltd | Wholesale & retail | 2017 |
| MD Flash Ltd | Administrative & support | 2014 |
| ME and MB Limited | Other services | 2020 |
| Meadow Drove Motors Ltd | Wholesale & retail | 2006 |
| Meadow View (Church Road) Management Limited | Households | 2009 |
| Meadowgate Lane Limited | Construction | 2018 |
| Meals Direct Limited | Manufacturing | 2025 |
| Meat Market Limited | Wholesale & retail | 1999 |
| Meddicc Ltd | Education | 2020 |
| Medworth Exports Limited | Wholesale & retail | 2018 |
| Meleric Ltd | Wholesale & retail | 2024 |
| Melton Agri Holdings Ltd | Financial services | 2025 |
| Melton Contracting Ltd | Agriculture & fishing | 2019 |
| Melton Soil Sampling Ltd | Agriculture & fishing | 2019 |
| Mend Care Ltd | Health & social care | 2022 |
| Mendhams Farm Ltd | Agriculture & fishing | 2022 |
| Mentha Nurseries Limited | Agriculture & fishing | 1991 |
| MER Construction Services Limited | Construction | 2013 |
| Mercan Investment Ltd | Real estate | 2026 |
| Mercery Limited | Manufacturing | 2022 |
| Meriadoc Ltd | Construction | 2014 |
| Merrison & Goodman Group Limited | Financial services | 2020 |
| Metaline Limited | Other services | 1979 |
| Metcalfe Copeman & Pettefar LLP | | 2012 |
| Mews Environmental Limited | Education | 2008 |
| MF Healthcare Limited | Health & social care | 2014 |
| MFM Land Surveys & Engineering Services Ltd | Construction | 2011 |
| MG Pharma Consult Ltd | Professional & scientific | 2018 |
| MG Property Holding Limited | Real estate | 2025 |
| Mgrade Limited | Construction | 2020 |
| MH Hoho Limited | Hospitality | 2018 |
| MH Smith Lettings Ltd | Real estate | 2024 |
| MHP Solutions Holdings Limited | Financial services | 2025 |
| Michael Mctaggart Limited | Construction | 2016 |
| Michaela Estates Limited | Construction | 2006 |
| Michal Bernacki Limited | Manufacturing | 2015 |
| Michelle Brown Greyhounds Limited | Extraterritorial | 2020 |
| Mick Watson Haulage Limited | Transport & logistics | 2003 |
| Middleton Construction Limited | Construction | 2015 |
| Midland Bridge LLP | | 2008 |
| Mildenhall Car Sales Ltd | Wholesale & retail | 2026 |
| Mile Tree Leisure Limited | Hospitality | 2025 |
| Mill Stainless Stockholders Limited | Wholesale & retail | 1978 |
| Millennium Estates Limited | Real estate | 2025 |
| Millennium Farming Company Limited | Agriculture & fishing | 2024 |
| Milleo Property Holdings Limited | Financial services | 2023 |
| Miller Walker & Co Ltd | Financial services | 2013 |
| Millsy Limited | Wholesale & retail | 2025 |
| Millthorne Developments Limited | Construction | 2016 |
| Milton Developments (Fenland) Limited | Construction | 2015 |
| Minds, Hearts & Lives Ltd | Health & social care | 2023 |
| Minx Beauty Consultants Limited | Other services | 2012 |
| Miramed Primary Health Ltd | Health & social care | 2025 |
| Missy DE Ltd | Wholesale & retail | 2018 |
| Mistick Limited | Households | 1989 |