| M&P Management Solutions Ltd | Financial services | 2025 |
| M&R Mobile Services Ltd | Wholesale & retail | 2024 |
| M&S Developers Limited | Real estate | 2020 |
| M&S Vekkal Group Limited | Hospitality | 2022 |
| M-Power Care Hub Ltd | Health & social care | 2026 |
| M. a. Jones Repointing Limited | Construction | 2002 |
| M. Anderson Construction Limited | Construction | 1987 |
| M. French Limited | Construction | 2002 |
| M.A.T. Cleaning & Janitorial Supplies Limited | Wholesale & retail | 2001 |
| M.B. Sports Construction Limited | Construction | 2005 |
| M.C.T. Holdings Limited | Professional & scientific | 2006 |
| M.I.N. Accountancy Limited | Professional & scientific | 2013 |
| M.J. & S.C. Collins Limited | Energy | 2011 |
| M.J. Green Construction Management Ltd | Construction | 2008 |
| M.J. Hickey Plumbing & Heating Ltd | Construction | 2004 |
| M.J.M.Data Capture Limited | Information & communication | 1990 |
| M.R.B. Associates Limited | Professional & scientific | 1989 |
| M.R.T Cleaning Services Ltd | Administrative & support | 2022 |
| M.S. Eagle Holdings Ltd | Financial services | 2025 |
| M23 Deluxe Ltd | Wholesale & retail | 2026 |
| M365 Stack Solutions Limited | Information & communication | 2025 |
| M82 Ltd | Transport & logistics | 2023 |
| MA Radiology Limited | Health & social care | 2018 |
| Maas Initiatives Limited | Professional & scientific | 2019 |
| Mabel and Friends Day Retreat Ltd | Other services | 2024 |
| Mablin Lodge Limited | Households | 1984 |
| MAC & ME Roasting Ltd. | Manufacturing | 2013 |
| MAC Design and Build Limited | Construction | 2004 |
| MAC Design Holdings Limited | Financial services | 2010 |
| MAC Design Investments Limited | Real estate | 2020 |
| MAC Real Estate Solutions Limited | Transport & logistics | 2024 |
| Mace Group Holdings UK Ltd | Financial services | 2025 |
| Mace Playce City Centre Ltd | Hospitality | 2019 |
| Macfarlane Acquisitions Limited | Real estate | 2011 |
| Machine Hire Limited | Manufacturing | 2001 |
| Machint Solutions Limited | Information & communication | 2017 |
| Machmo Limited | Financial services | 2024 |
| Machseh Ltd | Health & social care | 2026 |
| Mack Forensics Ltd | Professional & scientific | 2011 |
| Mackness Contracting Estates Limited | Real estate | 2021 |
| Mackness Contracting Limited | Administrative & support | 2007 |
| Maclean Building Supplies Ltd | Wholesale & retail | 2026 |
| Maclean Psychology Services Ltd | Health & social care | 2023 |
| Mactel IP Ltd | Other services | 2023 |
| Mada Sweet Cakes Ltd | Manufacturing | 2021 |
| Madaan Controls Limited | Information & communication | 2023 |
| Madaan Services Ltd | Real estate | 2019 |
| Maddison Health Limited | Health & social care | 2013 |
| Made by Jamie Limited | Households | 2014 |
| Made by Pink Limited | Professional & scientific | 2024 |
| Made Developments Limited | Real estate | 2024 |
| Made in Europe Express Limited | Transport & logistics | 1991 |
| Made in the Shade Limited | Information & communication | 2007 |
| Madelena Limited | Wholesale & retail | 2002 |
| Madide Fossor Limited | Hospitality | 2011 |
| Madison Arena Limited | Professional & scientific | 2025 |
| Madison Connections UK Limited | Hospitality | 2003 |
| Madison Heights Limited | Arts & recreation | 2000 |
| Madisons Group Limited | Construction | 2021 |
| MAF Financial Limited | Financial services | 2016 |
| MAG Construct Ltd | Construction | 2024 |
| Magcf Limited | Financial services | 2025 |
| Magenta Medical Services Ltd | Health & social care | 2024 |
| Magic Helping Hands Limited | Administrative & support | 2018 |
| Magic Helping Properties Ltd | Real estate | 2022 |
| Magic Torch PR Limited | Professional & scientific | 2011 |
| Magik Clean 10 Limited | Administrative & support | 2019 |
| Magnetic Ecology Limited | Manufacturing | 2004 |
| Magnivo Nominees Limited | Financial services | 2023 |
| Magnolia Limited | Financial services | 2011 |
| Magnus Tate Ltd | Real estate | 2021 |
| Magron Limited | Wholesale & retail | 2023 |
| Mahakot Limited | Information & communication | 2016 |
| Mahanaim City Church Ltd | Other services | 2020 |
| Mahlux Limited | Financial services | 2025 |
| MAID2CLEAN (Home Cleaners) Limited | Other services | 2013 |
| Maidens Barn Limited | Hospitality | 2011 |
| Maidens Events Ltd | Hospitality | 2020 |
| Mainpoint Care Limited | Health & social care | 2022 |
| Mainwaring Rail Ltd | Professional & scientific | 2014 |
| Mair Global Management Limited | Professional & scientific | 2014 |
| Majestic Electrical Services Ltd. | Construction | 2018 |
| Major Artists Limited | Arts & recreation | 2025 |
| Major Glass and Glazing Ltd. | Construction | 2014 |
| MAK Electrical Contracting Limited | Construction | 2013 |
| MAK LJO Limited | Wholesale & retail | 2023 |
| Makabile Ltd | Professional & scientific | 2023 |
| Make Holiday Memories Ltd | Administrative & support | 2019 |
| Make IT Big Productions Ltd | Arts & recreation | 2023 |
| Makee Construction Ltd | Construction | 2020 |
| Makee Ltd | Manufacturing | 2020 |
| Maker-Mends Limited | Other services | 1998 |
| Makkss Ltd | Wholesale & retail | 2025 |
| Malabar Eats Ltd | Hospitality | 2025 |
| Malcon Group Ltd | Construction | 2025 |
| Maldis Limited | Construction | 2021 |
| Maldon Building Contractors Limited | Extraterritorial | 2015 |
| Maldon Chandlery Limited | Wholesale & retail | 1994 |
| Maldon MOT Centre Limited | Wholesale & retail | 2024 |
| Maldon Oyster Company Ltd. | Agriculture & fishing | 2003 |