| M & a Fruit and Veg(Kings Lynn) Ltd | Households | 2024 |
| M & J Building & Maintenance Limited | Construction | 2016 |
| M & J Fabrications Ltd | Manufacturing | 2024 |
| M & J Groundworks Limited | Construction | 2016 |
| M & K Developers Limited | Construction | 2018 |
| M & N Coldstores Limited | Construction | 2014 |
| M & N Design & Build Limited | Construction | 2015 |
| M C Mallett Accountants Limited | Professional & scientific | 2017 |
| M Clarke Roofing Ltd. | Construction | 2022 |
| M Cousins & SON Ltd | Construction | 2011 |
| M Dobre Ltd | Health & social care | 2022 |
| M F Heavy Haulage Ltd | Transport & logistics | 2015 |
| M J Elliott & SON Limited | Manufacturing | 2024 |
| M L Sands Limited | Construction | 2011 |
| M Morgan Motor Engineer Limited | Wholesale & retail | 2001 |
| M Plus 2 Ltd | Administrative & support | 2023 |
| M Plus Growth Ltd | Information & communication | 2023 |
| M Plus Investments Limited | Real estate | 2022 |
| M Plus Investments Partnership LLP | | 2023 |
| M R Bathrooms Ltd | Construction | 2003 |
| M Sharp Driver Hire Limited | Transport & logistics | 2023 |
| M T Heritage Enterprises Ltd | Hospitality | 2022 |
| M W 5 Ltd | Hospitality | 2025 |
| M Williamson Developments Limited | Construction | 2008 |
| M&C Telecoms Limited | Professional & scientific | 2024 |
| M&D Painting & Decorating Ltd | Construction | 2017 |
| M-Tek Glass Ltd | Manufacturing | 2023 |
| M. H. Rains Limited | Agriculture & fishing | 1999 |
| M.A. Freight Services Limited | Transport & logistics | 1994 |
| M.C. Commercials Ltd | Wholesale & retail | 2005 |
| M.C. Nurse Limited | Construction | 1999 |
| M.E. Ayres & Sons Limited | Transport & logistics | 2002 |
| M.E. Ayres Holdings Limited | Transport & logistics | 2025 |
| M.G.Crisp(Narborough)Limited | Construction | 1954 |
| M.H. Rains (Holdings) Limited | Professional & scientific | 1999 |
| M.V.S Valeting Service Limited | Administrative & support | 2021 |
| M.W.Frost Anaesthetic Services Limited | Health & social care | 2010 |
| M.W.Smith Shellfish Limited | Agriculture & fishing | 2000 |
| MA - AI Limited | Transport & logistics | 2017 |
| Mabel Bakery Ltd | Hospitality | 2023 |
| Mabuza Group Ltd | Wholesale & retail | 2015 |
| Mabuza Valeting and Cleaning Ltd | Administrative & support | 2012 |
| Mackintosh EA Services Limited | Administrative & support | 2024 |
| Maclagan Studio Ltd | Arts & recreation | 2017 |
| Maclean Securities Limited | Financial services | 2006 |
| Macmillan Court (Bishopspark) Residents Association Limited | Households | 1992 |
| Macstanas Ltd | Transport & logistics | 2024 |
| Made by Field Ltd | Professional & scientific | 2019 |
| Madeinro Ltd | Wholesale & retail | 2020 |
| Madon Integrated AI Solutions Ltd | Information & communication | 2025 |
| MAG Power Networks Limited | Construction | 2025 |
| Magazine Leisure Ltd | Hospitality | 2014 |
| Magic Accommodations Ltd | Real estate | 2020 |
| Magic Couriers Ltd | Transport & logistics | 2017 |
| Magnifique Aesthetics & Beauty Ltd | Other services | 2020 |
| Magnolia Drive Management (KL) Limited | Households | 2017 |
| Magpie Security (Norfolk) Limited | Administrative & support | 2019 |
| Maintain Flight Level Ltd | Manufacturing | 2025 |
| Major Tea Co.Limited | Wholesale & retail | 1963 |
| Makes Sense Clothing Limited | Wholesale & retail | 2025 |
| Makroad Logistics Ltd | Transport & logistics | 2026 |
| Mallard Property Services Ltd | Hospitality | 2022 |
| Mallards (Massingham) Limited | Households | 2010 |
| Maltmas Farms Ltd | Agriculture & fishing | 2024 |
| Malvik Ltd | Wholesale & retail | 2025 |
| Mamdouh Group Ltd | Health & social care | 2025 |
| Mammoth Energy Solutions Limited | Construction | 2025 |
| Mamo Consultants Limited | Wholesale & retail | 2015 |
| Mandeep and Vishal Limited | Health & social care | 2025 |
| Mandeep Bhogal Limited | Health & social care | 2016 |
| Mandingo Enterprises Limited | Hospitality | 2018 |
| Mango Spice Ltd | Hospitality | 2025 |
| Mangocpcsdriver Limited | Construction | 2018 |
| Mann Made Developments Limited | Construction | 2010 |
| Manning Builders Ltd | Construction | 2022 |
| Manogize Ltd | Health & social care | 2023 |
| Manor Farm Barns Management (Harpley) Limited | Administrative & support | 1999 |
| Manor Farm Livery Limited | Extraterritorial | 2015 |
| Manorside Investments Ltd | Financial services | 2026 |
| Manser & Co Hair and Beauty Ltd | Other services | 2025 |
| Mantera Ltd | Transport & logistics | 2018 |
| Mapus Financial Planning Limited | Financial services | 2000 |
| Mapus Ltd | Financial services | 2025 |
| March Timber Supplies Ltd | Wholesale & retail | 2024 |
| Marct Properties Limited | Real estate | 2025 |
| Marg Limited | Health & social care | 2026 |
| Marham Hall Farms Holdings Limited | Financial services | 2024 |
| Marham LGV Driver Services Ltd | Transport & logistics | 2014 |
| Marine Court Management Company Limited | Real estate | 1982 |
| Maritime Mews Management Limited | Households | 1995 |
| Mark Donaldson (Norfolk) Limited | Hospitality | 2023 |
| Mark Pazik Ltd | Financial services | 2021 |
| Mark Poynton at Caistor Hall Limited | Hospitality | 2023 |
| Mark Spencer Services Limited | Transport & logistics | 2008 |
| Mark Tilbrook Properties Ltd | Real estate | 2026 |
| Marken Consultancy Group Limited | Information & communication | 2018 |
| Marken RE Specialty Limited | Financial services | 2018 |
| Marleys Cafe Ltd | Hospitality | 2019 |
| Marlin Holdings (Norfolk) Limited | Construction | 2012 |
| Marriott's Warehouse Limited | Hospitality | 2013 |