| M J Beckett & Sons Limited | Construction | 2003 |
| M Lacey Limited | Other services | 2005 |
| M Morrison Holdings Ltd | Real estate | 2024 |
| Magic Movies Ltd | Wholesale & retail | 2014 |
| Magnimate Ltd | Wholesale & retail | 2009 |
| Magnus Global Solutions Limited | Professional & scientific | 2018 |
| MAI Software Consulting Limited | Professional & scientific | 2025 |
| Maida Holdings Ltd | Wholesale & retail | 2020 |
| Major Scaffolding Limited | Construction | 2013 |
| Make-Uk Talent Solutions Limited | Administrative & support | 2009 |
| Malachite 364 Ltd | Professional & scientific | 2017 |
| Mali Investments Ltd | Real estate | 2023 |
| Mallie Ltd | Wholesale & retail | 2024 |
| Maltings Events Ltd | Hospitality | 2026 |
| Manor Nights Limited | Transport & logistics | 2009 |
| Manta AI Limited | Information & communication | 2026 |
| Mapleleaf Plumbing & Heating Ltd | Construction | 2019 |
| Marbla Homes Limited | Hospitality | 2019 |
| Marbla Limited | Construction | 2014 |
| Marine Systems (UK) Limited | Manufacturing | 1993 |
| Mark HIX Ltd | Hospitality | 2015 |
| Market Place Dental Limited | Administrative & support | 2017 |
| Markstan Consultants Limited | Professional & scientific | 2024 |
| Marlyn Memorabilia Limited | Wholesale & retail | 2026 |
| Marriage Estates Limited | Construction | 2022 |
| Marstan Facilities Limited | Construction | 2016 |
| Marsupium Limited | Manufacturing | 2026 |
| Martin P Watson Limited | Health & social care | 2012 |
| MAS Trading Limited | Financial services | 2013 |
| Masey MOO - Mason's Legacy | Other services | 2014 |
| Masters & Company Limited | Agriculture & fishing | 1926 |
| Mauro's in the Park Limited | Hospitality | 2014 |
| Mavtech Installation Limited | Construction | 2018 |
| Maysbrook Contracts Limited | Construction | 2022 |
| Mazra Farm Ltd | Agriculture & fishing | 2025 |
| Mckoy's Services Limited | Professional & scientific | 2012 |
| Mcrx Consultancy Limited | Professional & scientific | 2014 |
| Mead Rentals Limited | Real estate | 2026 |
| Meadow Oak Distillery Ltd | Manufacturing | 2021 |
| Medical Affairs Solutions Ltd | Health & social care | 2013 |
| Medicexpert Limited | Administrative & support | 2015 |
| Melitrade Limited | Construction | 2016 |
| Melon Property Corporation Ltd | Real estate | 2006 |
| Memor London Ltd | Wholesale & retail | 2020 |
| Memstech Ltd | Financial services | 2012 |
| Menhinick Contract Services Ltd | Agriculture & fishing | 2022 |
| Mente Hermosa CIC | Professional & scientific | 2023 |
| Merlins Trade Ltd | Professional & scientific | 2022 |
| Merth Limited | Health & social care | 2008 |
| Meteor Road RTM Company Limited | Households | 2018 |
| Mews Management (Dunmow) Limited | Other services | 2011 |
| MFK Associates Limited | Professional & scientific | 2023 |
| MHS Developments Limited | Construction | 2015 |
| Milano Cento (London) Ltd | Wholesale & retail | 2015 |
| Mill Lane Brewing Company Limited | Manufacturing | 2017 |
| Millie Beer Colour Consultancy Ltd | Professional & scientific | 2025 |
| Millspin Limited | Households | 2012 |
| Mimeartist Limited | Information & communication | 2007 |
| Mimmack Associates LLP | | 2010 |
| Minadrever Limited | Education | 2019 |
| Mind and Body Detox Ltd | Health & social care | 2016 |
| Mindset Marvels Limited | Wholesale & retail | 2025 |
| Mini Swimming Franchising Ltd | Arts & recreation | 2014 |
| Minty Highway Limited | Other services | 2004 |
| Minutemove Ltd | Transport & logistics | 2018 |
| Mission Construction Limited | Construction | 2004 |
| MIX and Flair Limited | Hospitality | 2014 |
| MJC Consulting Ltd | Information & communication | 2025 |
| MJH Rail Services Ltd | Construction | 2020 |
| MJS Car Storage Ltd | Transport & logistics | 2024 |
| MKB Precision Engineering Limited | Manufacturing | 2012 |
| Mncare Ltd | Health & social care | 2024 |
| Model My Ltd | Manufacturing | 2020 |
| Monk Media Ltd | Extraterritorial | 2009 |
| Monk Street Clinic Limited | Health & social care | 2021 |
| Montecristo Limited | Real estate | 1999 |
| Moonshadow Investments Ltd | Financial services | 2024 |
| Mordrick Consulting Ltd | Professional & scientific | 2018 |
| Morgan's Shoe Repairs Ltd | Wholesale & retail | 2019 |
| Morning Star Community Care Ltd | Health & social care | 2021 |
| Morrison & Tokley Limited | Other services | 2015 |
| Movers of Cambridge Limited | Transport & logistics | 1994 |
| MPA Independent Services Ltd | Transport & logistics | 2011 |
| MR & JL Ritchie Ltd | Agriculture & fishing | 2020 |
| MRS M'S Sweets Ltd | Wholesale & retail | 2021 |
| MSU Consultancy Ltd | Professional & scientific | 2013 |
| MTL Commodities Ltd | Wholesale & retail | 2019 |
| MTM Group Holdings Ltd | Hospitality | 2025 |
| Mulgrave Services Ltd | Transport & logistics | 2016 |
| Mullens & Associates Limited | Professional & scientific | 2020 |
| Multiple Property Limited | Real estate | 2026 |
| Mumz Diner Ltd | Hospitality | 2024 |
| Munson and Munson Limited | Information & communication | 2013 |
| Murphy's Building Services Ltd | Construction | 2019 |
| Must Migrate Limited | Extraterritorial | 2008 |
| Mutlows Limited | Education | 2013 |
| Mwendaz PVT Ltd | Health & social care | 2018 |
| My Travel Essentials Limited | Other services | 2016 |
| Myco Wimbish Limited | Wholesale & retail | 2021 |
| Myriammy Ltd | Health & social care | 2019 |