| Mark Hope Consulting Limited | Professional & scientific | 2010 |
| Mark Nicholas Estates Limited | Real estate | 2006 |
| Mark of Distinction Construction Limited | Construction | 2012 |
| Markap Ltd | Health & social care | 2023 |
| Market Street Grocers & OFF License Ltd | Wholesale & retail | 2023 |
| Markitplace Ltd | Information & communication | 2020 |
| Marland Lawns Ltd | Administrative & support | 2026 |
| Marland Properties Ltd | Real estate | 2015 |
| Marlec Industrial Services Limited | Professional & scientific | 2013 |
| Marlo Products Limited | Wholesale & retail | 2004 |
| Mars Car Sales Limited | Wholesale & retail | 2016 |
| Mars Group Ltd | Real estate | 2026 |
| Mars Selkirk Ltd | Real estate | 2026 |
| Marsh Capital Ltd | Financial services | 2018 |
| Marsh Finance & Commercial (NW1) Ltd | Professional & scientific | 2011 |
| Marsh Finance & Commercial Limited | Financial services | 1999 |
| Marsh Finance Limited | Financial services | 1973 |
| Marsh FM LLP | | 2009 |
| Marsh Furbs | Financial services | 2014 |
| MART4EVERYONE Ltd | Wholesale & retail | 2025 |
| Martacastro Consulting Limited | Information & communication | 2018 |
| Marthi Limited | Real estate | 2007 |
| Marthi Medical Services Ltd | Health & social care | 2021 |
| Martin & SON Joinery Ltd | Construction | 2020 |
| Martins Design Ltd | Professional & scientific | 2025 |
| Martins Mill Limited | | 1932 |
| Martlet Films Ltd | Arts & recreation | 2025 |
| Marygold Services Ltd | Health & social care | 2015 |
| Marzouk Holdings Ltd | Financial services | 2023 |
| MAS Solutions Limited | Wholesale & retail | 2019 |
| Masica Wash Limited | Wholesale & retail | 2025 |
| Mason Heating Ltd | Construction | 2019 |
| Mason's Events Corporation Limited | Manufacturing | 2025 |
| Massala Takeaway Ltd | Hospitality | 2025 |
| Master Cleaning Solutions Ltd | Administrative & support | 2025 |
| Masterclass E-Books Limited | Information & communication | 2025 |
| Masterfit Kitchens Ltd | Construction | 2024 |
| Mastextile Limited | Manufacturing | 2017 |
| Mathew Health Care Ltd | Health & social care | 2020 |
| Matimo Constructions Limited | Real estate | 2019 |
| Matthew Ashworth Transport Ltd | Transport & logistics | 2025 |
| Matthew Hughes Ltd | Health & social care | 2021 |
| Matthews Group Holdings Limited | Financial services | 2024 |
| Matthews Meats Limited | Manufacturing | 2020 |
| Mattunicorn Ltd | Information & communication | 2024 |
| Maty TEE Limited | Health & social care | 2019 |
| MATZ92 Ltd | Construction | 2019 |
| Maverick LAB CIC | Education | 2019 |
| Mawj Marketing Limited | Information & communication | 2025 |
| MAX Venture Ltd | Manufacturing | 2021 |
| Maxblue Limited | Wholesale & retail | 2022 |
| Maxeo Ltd | Professional & scientific | 2019 |
| Maxgear Limited | Wholesale & retail | 2009 |
| Maximas Mahmood Ltd | Extraterritorial | 2026 |
| Maximum Marketing Limited | Professional & scientific | 2005 |
| Maxtread Rochdale Ltd | Wholesale & retail | 2019 |
| Maxwell Melia Academy Limited | Education | 2017 |
| Maxx Gear Ltd | Wholesale & retail | 2022 |
| Maya Akram Limited | Health & social care | 2023 |
| Maydaveltd Ltd | Wholesale & retail | 2026 |
| Mayer Skip & Excavation Hire Limited | Water & waste | 2016 |
| Mayfair Apparel Ltd | Wholesale & retail | 2026 |
| Mayfair Grand Ltd | Real estate | 2023 |
| Mayfield Carpets Limited | Wholesale & retail | 2001 |
| Mayfield Garage (UK) Ltd | Wholesale & retail | 2008 |
| Mayfield Grange Investments Ltd | Real estate | 2018 |
| Mayfield Internal Audit and Consulting Limited | Professional & scientific | 2010 |
| Mayfield Vehicle Repairs Ltd | Administrative & support | 2007 |
| Mayo (Winsford) Ltd | Construction | 2024 |
| Mayo Appliances Ltd | Wholesale & retail | 2025 |
| Mayo Civil Engineering (Elswick) Limited | Construction | 2020 |
| Mayo Civil Engineering (Longridge) Limited | Construction | 2020 |
| Mayo Civil Engineering Limited | Construction | 2005 |
| Mayo Civils Limited | Extraterritorial | 2013 |
| Mayo Developments (Station Quarter) Ltd | Construction | 2025 |
| Mazda & Mitsubishi Spares Limited | Administrative & support | 2006 |
| Mazhar ALI Limited | Administrative & support | 2019 |
| Mazurek Delikatesy Ltd | Wholesale & retail | 2020 |
| MB General Cleaning Limited | Administrative & support | 2023 |
| MB Inc Limited | Wholesale & retail | 2021 |
| MB Schoolwear Specialist Ltd | Manufacturing | 2015 |
| MB Shahid Anaesthesia Ltd | Health & social care | 2026 |
| MB22 Restaurant Ltd | Hospitality | 2025 |
| MBO Logistics Ltd | Transport & logistics | 2026 |
| MBP LG Promotions Ltd | Arts & recreation | 2022 |
| MBP MC Promotions Ltd | Arts & recreation | 2021 |
| MBP Promotions Ltd | Arts & recreation | 2019 |
| MBW Projects Limited | Construction | 2024 |
| MC Rochdale Ltd | Hospitality | 2026 |
| MC Wealth Ltd | Professional & scientific | 2023 |
| Mc&A Elite Furniture Services Ltd | Manufacturing | 2024 |
| Mccarroll Homes Ltd | Real estate | 2022 |
| Mccormack-Hse-Fm Limited | Professional & scientific | 2023 |
| MCE Medical Market Research Ltd | Professional & scientific | 2013 |
| MCE Smart Hub Ltd | Manufacturing | 2026 |
| MCH Properties North Limited | Real estate | 2020 |
| Mcintosh-Gordon Accountants Ltd | Professional & scientific | 2025 |
| Mcjessop Property Solutions Ltd | Real estate | 2019 |
| Mcnally Wild Limited | Professional & scientific | 2014 |
| MCP Sales Limited | Wholesale & retail | 2011 |