| Mcpike's Brewing Limited | Manufacturing | 2021 |
| MDM Connections Ltd | Professional & scientific | 2023 |
| Meadow Green Farm Services Limited | Information & communication | 2010 |
| Meat Inn of Haverhill Ltd | Wholesale & retail | 2021 |
| MEDICS24 Limited | Health & social care | 2005 |
| Medstat (Suffolk) Limited | Professional & scientific | 2013 |
| Meila Ltd | Manufacturing | 2023 |
| MEL Aviation Limited | Professional & scientific | 1968 |
| MEL Aviation Trustee Limited | Financial services | 2025 |
| MEL Thompson Design Limited | Information & communication | 2014 |
| Melcarpentry&Construction Ltd | Construction | 2026 |
| Melford CNC Limited | Hospitality | 2025 |
| Mellow Salon Ltd | Other services | 2017 |
| Mercury Building Services Limited | Construction | 2008 |
| Merlin Systems Specialist Ltd | Wholesale & retail | 2020 |
| Mersea Carpets Limited | Wholesale & retail | 1987 |
| Metals Daily Ltd | Information & communication | 2019 |
| Mette Davis-Garratt Limited | Professional & scientific | 2016 |
| Meze Mangal Ltd | Hospitality | 2023 |
| MH & MH Holdings Ltd | Financial services | 2024 |
| MH Sales and Marketing Ltd | Administrative & support | 2025 |
| MHT Civil Engineering Ltd | Construction | 2013 |
| MIA MOO Ltd | Manufacturing | 2020 |
| Miaptica Consulting Ltd | Professional & scientific | 2026 |
| Micco Associates Ltd | Professional & scientific | 2023 |
| Microcharge Property Ltd | Financial services | 2026 |
| Microcharge Systems Limited | Manufacturing | 1999 |
| Midsomer Mews Limited | Households | 2020 |
| MIG Group Limited | Financial services | 2015 |
| Mike Bithell Games Limited | Information & communication | 2013 |
| Mike Webb Associates | | 1994 |
| Mill Kitchens Limited | Administrative & support | 1997 |
| Mill Lane Management Company Limited | Households | 1999 |
| Mill Street Stores (Armthorpe) Limited | Real estate | 1966 |
| Millers Renovation Management Ltd | Construction | 2019 |
| Milton Chiropractic Limited | Health & social care | 2008 |
| Minden Road East Limited | Hospitality | 1996 |
| Mini Model Merchant Limited | Wholesale & retail | 2021 |
| Mini Waste Limited | Water & waste | 2015 |
| Mini Waste Skip Hire Limited | Extraterritorial | 2015 |
| Misty Media Ltd | Information & communication | 2022 |
| Mja-Ps Ltd | Construction | 2019 |
| MJE Consultancy Suffolk Ltd | Professional & scientific | 2026 |
| MJH Farming Solutions Limited | Agriculture & fishing | 2011 |
| MJK Consulting Services Ltd | Administrative & support | 2025 |
| MJN Computing Ltd | Information & communication | 2026 |
| MJO Electrical (Essex) Limited | Construction | 2012 |
| Mjpr Plant Limited | Manufacturing | 2020 |
| MK1 Refrigeration Ltd | Manufacturing | 2024 |
| Mo's Caribbean Cookhouse Ltd | Hospitality | 2025 |
| Mode 7 Limited | Information & communication | 2003 |
| Modus Gauges Limited | Wholesale & retail | 1990 |
| Momi Construction Ltd | Construction | 2017 |
| Momi Investment Ltd | Real estate | 2020 |
| Monro Estates Limited | Construction | 2014 |
| Montana Gardens (Sutton) Management Company Limited | Households | 1997 |
| Montgomery Court Limited | Households | 2017 |
| Moody Harrison Medical Limited | Health & social care | 2016 |
| Mooncast Films Ltd | Professional & scientific | 2018 |
| Moonlight Acquisitions (L) Limited | Construction | 2021 |
| Moonlight Acquisitions Limited | Construction | 2021 |
| Moorfield (Easington) Management Company Limited | Households | 2019 |
| More Than Pretty Pictures Architects Ltd | Professional & scientific | 2021 |
| Morgan Harvey Logistics Ltd | Transport & logistics | 2015 |
| Morgan Home Decor Ltd | Wholesale & retail | 2023 |
| Mortlake Food & Wines Ltd | Wholesale & retail | 2019 |
| Mosaic Biopharma Consulting Ltd | Professional & scientific | 2021 |
| Motor Repair Centre Ltd | Wholesale & retail | 2016 |
| Mount Farm Vineyards Ltd | Agriculture & fishing | 2018 |
| MR Adam Howard Ltd | Health & social care | 2019 |
| MR G H RIX Frcs (Urol) Ltd | Health & social care | 2010 |
| MR J S Stanton Limited | Health & social care | 2012 |
| MR Nicholas Wardle Frcs (Orth) Limited | Health & social care | 2013 |
| MRG Estate Planning Services Ltd | Professional & scientific | 2024 |
| Mskambo Ltd | Hospitality | 2018 |
| MSL Fabrications Ltd | Administrative & support | 2019 |
| Msteelsot Limited | Wholesale & retail | 2012 |
| MTM Plant & Sales Limited | Administrative & support | 1983 |
| MTP Plumbing & Heating Limited | Construction | 2021 |
| Mulberry Buildings Ltd | Financial services | 2025 |
| Mulberry Bush Day Nursery (Mulbarton) Ltd | Education | 2003 |
| Mulberry Bush Day Nursery (Wymondham) Limited | Education | 2009 |
| Mulberry Games Limited | Manufacturing | 2022 |
| Multicoach Ltd | Education | 2022 |
| Multipom Limited | Wholesale & retail | 2014 |
| Murray International Partners Limited | Professional & scientific | 2020 |
| Murrayman Ltd | Wholesale & retail | 2014 |
| Mwah Limited | Arts & recreation | 2007 |
| My Butterfly Living Ltd | Wholesale & retail | 2026 |
| My Devilish Desires Ltd | Wholesale & retail | 2024 |
| Mydas PR and Marketing Limited | Professional & scientific | 2013 |
| Mymatespace Ltd | Information & communication | 2021 |
| N & C Electrical Limited | Construction | 2012 |
| N C Warden Associates Limited | Other services | 2012 |
| N Display Ltd | Manufacturing | 2016 |
| N W K Services Ltd. | Wholesale & retail | 1976 |
| N-Star Services Limited | Administrative & support | 2025 |
| N. E. Cutts Limited | Construction | 1979 |
| N.R Property Maintenance Ltd | Construction | 2014 |
| Naba EN Limited | Construction | 2021 |