| Midlands Hire Limited | Administrative & support | 2023 |
| Midlands Pro IT and Telecoms Limited | Information & communication | 2025 |
| Midlands Pro IT Services Limited | Information & communication | 2017 |
| Midlands Roofing and Guttering Ltd | Construction | 2022 |
| Midnorthern Ltd | Professional & scientific | 2015 |
| MIG Eyewear Limited | Wholesale & retail | 2010 |
| Mike Harley Building Contractors Limited | Construction | 2008 |
| Mikki Longley Creative Limited | Professional & scientific | 2015 |
| Milestone Projects Ltd | Construction | 2022 |
| Mill Hill Interiors Limited | Manufacturing | 2012 |
| Mill Hill Lane Management Company Limited | Households | 2018 |
| Millcroft Ventures Ltd | Construction | 2015 |
| Millie’S Bakery Ltd | Manufacturing | 2024 |
| Millrose Legal Limited | Professional & scientific | 2025 |
| Milo's Innovative Limited | Hospitality | 2022 |
| Milo's of Market Harborough Limited | Hospitality | 2011 |
| Mimi's Catering Ltd | Hospitality | 2025 |
| Mind Body Health Limited | Administrative & support | 2013 |
| Mind Talk Ltd | Health & social care | 2014 |
| Minster Commercial Property Ltd | Construction | 2019 |
| Minster Property Group (Bassingbourn) Ltd | Construction | 2026 |
| Minster Property Group (Bodicote) Ltd | Construction | 2023 |
| Minster Property Group (Braunston) Ltd | Construction | 2023 |
| Minster Property Group (Burwell) Ltd | Construction | 2023 |
| Minster Property Group (Castle Bytham) Ltd | Construction | 2022 |
| Minster Property Group (Clenchwarton) Ltd | Construction | 2023 |
| Minster Property Group (Crick) Ltd | Construction | 2019 |
| Minster Property Group (Fenstanton) Ltd | Construction | 2023 |
| Minster Property Group (Glastonbury) Ltd | Construction | 2026 |
| Minster Property Group (Haverhill) Ltd. | Construction | 2023 |
| Minster Property Group (Houghton on the Hill) Ltd | Construction | 2022 |
| Minster Property Group (Marham) Ltd | Construction | 2026 |
| Minster Property Group (Narborough 2) Ltd | Construction | 2023 |
| Minster Property Group (Newborough) Ltd | Construction | 2022 |
| Minster Property Group (Orwell) Ltd | Construction | 2022 |
| Minster Property Group (Sutton Benger) Ltd | Construction | 2023 |
| Minster Property Group (Uppingham) Ltd | Construction | 2025 |
| Minster Property Group (Yarwell) Ltd | Construction | 2024 |
| Minster Property Group Ltd | Construction | 2018 |
| Mint Eco Clean Limited | Manufacturing | 2022 |
| Mint Holdings Limited | Financial services | 2007 |
| Mint Portfolio Limited | Real estate | 2011 |
| Miracle Moon Limited | Wholesale & retail | 2022 |
| Mistero Limited | Hospitality | 2015 |
| Mistryk Ltd | Professional & scientific | 2023 |
| Mitch Holdings Limited | Professional & scientific | 2025 |
| Mitchell Coaching Services Limited | Education | 2025 |
| Mixtum Estates Ltd | Real estate | 2024 |
| MJ Engineering Limited | Manufacturing | 1988 |
| MJ Toolmakers Limited | Manufacturing | 2002 |
| MJB Medical & Event Services Ltd | Other services | 2018 |
| MJF Carta Ltd | Professional & scientific | 2024 |
| MJM Building Management Ltd | Households | 2026 |
| MJM Home & Garden Ltd | Construction | 2026 |
| MK Building Solutions, Design & Build Ltd | Construction | 2016 |
| Mkcp Consulting Limited | Information & communication | 2016 |
| MKF Transport & Distribution Ltd | Transport & logistics | 2015 |
| MM Construction Projects Ltd | Construction | 2007 |
| Mmljd Consulting Limited | Information & communication | 2026 |
| MMY Ltd | Professional & scientific | 2001 |
| Mobilevalley Employee Ownership Trustee Ltd | Administrative & support | 2023 |
| Mobilevalley Limited | Professional & scientific | 2004 |
| Moguntia Food Group UK Limited | Wholesale & retail | 2010 |
| Moguntia Food Limited | Wholesale & retail | 2009 |
| Momentum Circuits Ltd | Other services | 2013 |
| Momentum Rise Limited | Professional & scientific | 2025 |
| Mont Blanc Enterprises Limited | Professional & scientific | 2013 |
| Monte Carvoeiro UK Limited | Hospitality | 2009 |
| Monty Motorsport Limited | Arts & recreation | 2024 |
| Mooi ADJ Beauty Limited | Other services | 2019 |
| Moomins Catering Ltd | Hospitality | 2020 |
| Moondrops Recruitment Services Ltd | Administrative & support | 2025 |
| Moose House of Hair Ltd | Other services | 2017 |
| Moot Hill Limited | Professional & scientific | 2018 |
| Morrell Property Co Ltd | Real estate | 2026 |
| Morrison & Morrison Limited | Manufacturing | 2025 |
| MOS Building Services Ltd | Construction | 2016 |
| Mosaic Estates (Midlands) Limited | Real estate | 2004 |
| Mosaic Projects and Investments Ltd | Construction | 2005 |
| Moscar Moor LLP | | 2016 |
| Moss & Spoor Consultancy Ltd | Professional & scientific | 2018 |
| Moss & Spoor Property Ltd | Real estate | 2018 |
| Mossco Trading Limited | Financial services | 2026 |
| Moultonsoftware Ltd | Wholesale & retail | 2025 |
| Mousait Ltd | Information & communication | 2023 |
| Moving Soles Ltd | Wholesale & retail | 2025 |
| Mowsley Court Management Company Limited | Households | 1976 |
| Mowsley Investments Ltd | Professional & scientific | 2023 |
| MR & MR Properties Limited | Real estate | 2024 |
| MRN Consulting Limited | Information & communication | 2013 |
| MSA Coast Transport Limited | Transport & logistics | 2016 |
| Msquare Architects Limited | Professional & scientific | 2010 |
| Msrt Maintenance Limited | Manufacturing | 2025 |
| MSS Professional Smokecloak Limited | Construction | 2015 |
| Mujovi Ltd | Administrative & support | 2018 |
| Mulberry HR Consulting Ltd | Administrative & support | 2025 |
| Multi Resource Marketing (Holdings) Limited | Financial services | 2016 |
| Multi Resource Marketing Limited | Administrative & support | 2003 |
| Munton Roofing Contractors Limited | Construction | 2007 |
| Murdoch Student Homes Limited | Real estate | 2007 |