| M&W JAY Limited | Construction | 2004 |
| M&W JAY Park Homes Limited | Real estate | 2008 |
| M.Bloomfield & Sons Limited | Real estate | 1963 |
| M.C. ROE Agricultural Services Ltd | Agriculture & fishing | 2020 |
| Mack Heating Services Limited | Construction | 2018 |
| Macrae Inn Ltd | Hospitality | 2017 |
| Maestros Academy Ltd | Arts & recreation | 2019 |
| Magic Carpet Audio Visual Ltd | Professional & scientific | 2022 |
| Magnatu Ltd | Construction | 2021 |
| Magnifye Limited | Professional & scientific | 2007 |
| Mainstream Entertainment Limited | Arts & recreation | 2025 |
| Malom Ltd | Professional & scientific | 2019 |
| Maltdoctor Ltd | Professional & scientific | 2021 |
| Maltster's Yard Management Co Limited | Real estate | 2010 |
| Maltwell Consulting Limited | Professional & scientific | 2025 |
| Mama Nourish Ltd | Wholesale & retail | 2020 |
| Management and Marine Supplies Limited | Administrative & support | 2017 |
| Mandarin 228 Ltd | Hospitality | 2021 |
| Mandatory Performance Ltd | Manufacturing | 2024 |
| Mandox Limited | Real estate | 2003 |
| Manifesto Strategy Limited | Professional & scientific | 2012 |
| Manlay Limited | Hospitality | 2025 |
| Manor Drive Ltd | Information & communication | 2019 |
| Manor Farm Community Energy Limited | Professional & scientific | 2013 |
| Maple Financial Management Limited | Professional & scientific | 2024 |
| Marcus Smith Property Developments Limited | Construction | 2019 |
| Marcus Smith Tiling Limited | Construction | 2017 |
| Margetts Advisory & Support Services Limited | Professional & scientific | 2010 |
| Marigot Ltd | Real estate | 2025 |
| Marindrew Ltd | Information & communication | 2016 |
| Marine Team Ltd | Construction | 2022 |
| Marisail Ltd | Manufacturing | 2023 |
| Maritlink Limited | Households | 1999 |
| Mark Buckle Electrician Ltd | Construction | 2004 |
| Mark's Delivery Services Ltd | Transport & logistics | 2015 |
| Marlowe Medical Limited | Health & social care | 2026 |
| Marsh Software Ltd | Extraterritorial | 2019 |
| Marshall's Meadow Management Company Limited | Households | 2000 |
| Martial Arts Stowmarket: HAN GUK MU Sool Ltd | Arts & recreation | 2024 |
| Martin Buckett Limited | Information & communication | 2024 |
| Martin Jewers Consulting Ltd | Professional & scientific | 2014 |
| Martin Mounsey Limited | Wholesale & retail | 2012 |
| Marvel Care Ltd | Health & social care | 2022 |
| Masala Moussaka Ltd | Wholesale & retail | 2024 |
| Master Wong Limited | Health & social care | 2017 |
| Matrix Thinking Ltd | Professional & scientific | 2024 |
| Maxfr Limited | Wholesale & retail | 2022 |
| MB Trees (East Anglia) Limited | Other services | 2004 |
| MBC Electrical Testing Limited | Construction | 2009 |
| MC Build & Renovations Ltd | Construction | 2025 |
| Mccartan's Limited | Hospitality | 2001 |
| Mcfox Capital Ltd | Wholesale & retail | 2025 |
| Mcfox Group Ltd | Financial services | 2024 |
| Mcfox Properties Ltd | Real estate | 2024 |
| Mcfox Renovates Ltd | Real estate | 2025 |
| Mcfox Services Limited | Administrative & support | 2025 |
| Mcfox Stays Ltd | Real estate | 2025 |
| Mcmyn Limited | Construction | 2005 |
| Mcnamara Motors Limited | Administrative & support | 1930 |
| Mcneill Property (Maidstone) Limited | Real estate | 2023 |
| MD Watson Consulting Limited | Professional & scientific | 2018 |
| Mechanic INK Ltd | Information & communication | 2019 |
| Medspares Ltd | Manufacturing | 2018 |
| MEG OH Designs Limited | Professional & scientific | 2022 |
| Megan Kate Performing Arts Ltd | Arts & recreation | 2020 |
| Menacing Media Trading LLP | | 2019 |
| Mendes EN Ltd | Hospitality | 2023 |
| Mendlesham Holdings Ltd | Financial services | 2026 |
| Meridius Services Limited | Real estate | 2008 |
| Merlin Oak Properties Limited | Real estate | 2024 |
| Messages From DAD Ltd | Arts & recreation | 2026 |
| Metal Solutions UK 2015 Limited | Professional & scientific | 2015 |
| Metis QA Consulting Ltd | Professional & scientific | 2022 |
| Michael Belcher Limited | Construction | 1971 |
| Michael Hayden Properties Ltd | Real estate | 2017 |
| Michaels Butchers Limited | Wholesale & retail | 2003 |
| Mickfield Timber Products Ltd | Manufacturing | 2023 |
| Micof Ltd | Transport & logistics | 2024 |
| Micropulse Ltd | Professional & scientific | 2022 |
| MID Suffolk Holdings Limited | Real estate | 2020 |
| MID Suffolk Mobility Limited | Wholesale & retail | 2004 |
| MID Suffolk Physiotherapy Ltd | Health & social care | 2019 |
| Middy Trading Co. Ltd | Wholesale & retail | 1998 |
| Midlands Technical Support Limited | Wholesale & retail | 2012 |
| Mike Dawe Ltd | Administrative & support | 2016 |
| Mike Hammond Consultancy Ltd | Professional & scientific | 2016 |
| Miles Crop Cover Limited | Wholesale & retail | 2001 |
| Miles Garrod Electrical Limited | Construction | 2006 |
| Miles Vartan Consultancy Limited | Professional & scientific | 2009 |
| Mill Gardens Mgmt Co. Ltd | Households | 2026 |
| Mill Saddlery (Suffolk) Ltd | Wholesale & retail | 2002 |
| Mindhug Impact CIC | Public administration | 2025 |
| Mindhug Ltd | Health & social care | 2019 |
| Mingle Studio Ltd | Information & communication | 2018 |
| Ministry Leadership and Services Ltd | Other services | 2021 |
| Mirabyte Ltd | Information & communication | 2024 |
| Mirage Cosmetics Ltd | Wholesale & retail | 2008 |
| Mirage X Limited | Information & communication | 2022 |
| Miyagi Limited | Manufacturing | 2014 |
| MJC Property Investments Limited | Real estate | 2026 |