| M & S Enterprises Limited | Real estate | 1986 |
| M & Y Air Conditioning Limited | | 1989 |
| M & Z Developments (UK) Ltd | Real estate | 2013 |
| M a L Contract Services Limited | Construction | 1998 |
| M a Ward Farms Ltd | Agriculture & fishing | 2013 |
| M B Accident Repair Centre Limited | Wholesale & retail | 2013 |
| M Brind Consulting Ltd | Information & communication | 2018 |
| M Buivydas Ltd | Construction | 2019 |
| M C Mann Management Ltd | Real estate | 2023 |
| M Car Traders Ltd | Wholesale & retail | 2025 |
| M Chisnall & Sons Limited | Construction | 1999 |
| M D E Electrical Supplies Limited | Administrative & support | 2003 |
| M D Groundworks & Construction (Anglia) Ltd | Construction | 2025 |
| M F Gallery and Framing Limited | Wholesale & retail | 2014 |
| M F T Couriers Ltd | Transport & logistics | 2014 |
| M Greenwood Ltd | Transport & logistics | 2021 |
| M H Consultancy Solutions Ltd | Construction | 2024 |
| M Hall Carpentry Ltd | Construction | 2022 |
| M J Bardwell (Contractors) Limited | Construction | 1991 |
| M J M Curry Spice Ltd | Hospitality | 2018 |
| M J Smith Transport Limited | Transport & logistics | 1997 |
| M Jarrald Construction and Carpentry Ltd | Administrative & support | 2019 |
| M L Autocare Ltd | Wholesale & retail | 2017 |
| M M Self Ltd | Agriculture & fishing | 2013 |
| M Pakalka Ltd | Construction | 2022 |
| M R Catering Limited | Manufacturing | 2025 |
| M R W Trading Limited | Wholesale & retail | 2004 |
| M Sea Transport Ltd | Transport & logistics | 2016 |
| M&A Services (EN) Ltd | Wholesale & retail | 2017 |
| M&C Colours Ltd | Manufacturing | 2024 |
| M&C Locksmiths Ltd | Other services | 2026 |
| M&D Lazar Transport Ltd | Transport & logistics | 2018 |
| M&Hera Ltd | Wholesale & retail | 2025 |
| M&J Bristol (UK) Ltd | Professional & scientific | 2023 |
| M&L Healthcare Solutions Limited | Financial services | 2009 |
| M&M and Sons Transport Ltd | Administrative & support | 2015 |
| M&M Ipswich Limited | Real estate | 2024 |
| M&M Properties (Stamford) Ltd | Construction | 2023 |
| M&M Property Heaven Ltd | Real estate | 2025 |
| M&N Investments Limited | Real estate | 2014 |
| M&N Ipswich Management Ltd | Construction | 1999 |
| M&U Cleaning Services Ltd | Administrative & support | 2012 |
| M&V Cabs Ltd | Transport & logistics | 2025 |
| M-Prime Limited | Construction | 2022 |
| M. Brewer Limited | Real estate | 1974 |
| M. Chisnall Holdings Ltd | Financial services | 2024 |
| M. D. R. Hydrographic Ltd | Professional & scientific | 2008 |
| M. Eley Plumbing & Heating Services Ltd | Construction | 2011 |
| M. Hancock Wealth Management Ltd | Administrative & support | 2009 |
| M. Marney Limited | Administrative & support | 1978 |
| M.A.C.E. (Shipping) Limited | Transport & logistics | 1983 |
| M.A.F Property Services Ltd | Construction | 2015 |
| M.A.R.O Supplies Ltd | Wholesale & retail | 2023 |
| M.A.T. Electrical Contractors Limited | Construction | 2011 |
| M.C. Contracts Limited | Construction | 2001 |
| M.G.Motorcycles Limited | Wholesale & retail | 2019 |
| M.J. Souster (Ipswich) Limited | Wholesale & retail | 1977 |
| M.M & K.E Limited | Real estate | 2023 |
| M.Smith Building Ltd | Construction | 2026 |
| M11R Software Limited | Information & communication | 2025 |
| M3TS Ltd | Administrative & support | 2018 |
| M42 Ltd | Information & communication | 2017 |
| M9 Creative Limited | Information & communication | 2014 |
| MA Convenience Store Ltd | Wholesale & retail | 2025 |
| Mabo Investments Limited | Real estate | 2026 |
| Mabzal Healthcare Limited | Health & social care | 2016 |
| MAC Cheriton Limited | Information & communication | 2014 |
| MAC Construction (Anglia) Limited | Construction | 2002 |
| MAC Estate Management Ltd | Real estate | 2024 |
| MAC Estates Limited | Construction | 1985 |
| Macbros Group Ltd | Other services | 2024 |
| Macc International Limited | Professional & scientific | 1995 |
| Macfinder Limited | Information & communication | 2009 |
| Macfiz Ltd | Other services | 2023 |
| Mackenzie Pack Limited | Administrative & support | 2008 |
| Mackinder Accountancy Ltd | Professional & scientific | 2024 |
| Maclau Ltd | Real estate | 2024 |
| Maco Tour Tras Ltd | Transport & logistics | 2023 |
| Macrefresh Ltd | Manufacturing | 2010 |
| Macs Scaff Limited | Construction | 2022 |
| MAD Sound Productions Ltd | Arts & recreation | 2025 |
| MAD Supps Ltd | Wholesale & retail | 2025 |
| Mad-Hr Holdings Ltd | Financial services | 2026 |
| Mad-Hr Ltd | Professional & scientific | 2014 |
| Mada Services Ltd | Transport & logistics | 2016 |
| Maddette Limited | Administrative & support | 2021 |
| Maddison House Hotel Limited | Real estate | 2021 |
| Made 2 Measure Interiors Ltd | Manufacturing | 2018 |
| Made by the Forge Limited | Manufacturing | 2007 |
| Made Easy Ltd | Real estate | 2005 |
| Made MEN Music and Management Limited | Arts & recreation | 2023 |
| Made Peachy Ltd | Information & communication | 2013 |
| Made Tech IT Ltd | Information & communication | 2017 |
| Madeforjames Ltd | Manufacturing | 2020 |
| Madeleinerose Ltd | Administrative & support | 2025 |
| Madew Investments Limited | Real estate | 2023 |
| Madhav World Ltd | Wholesale & retail | 2026 |
| Madley Developments Ltd | Construction | 2026 |
| Madness Transport Ltd | Wholesale & retail | 2025 |
| Madu Transport Ltd | Transport & logistics | 2025 |