| Maine Business Systems Limited | Wholesale & retail | 1987 |
| Majadu Limited | Wholesale & retail | 2007 |
| Majc Associates Limited | Transport & logistics | 2001 |
| Majendi Limited | Information & communication | 2006 |
| Majestic Construction & Design Ltd | Construction | 2026 |
| Majestic Trades 2026 Ltd | Construction | 2026 |
| Makco (UK) Limited | Professional & scientific | 2000 |
| Makesure Limited | Information & communication | 1996 |
| Makevasy Ltd | Construction | 2024 |
| Makeyour-Point Limited | Information & communication | 2002 |
| Makjay Pharmaceutical Limited | Manufacturing | 1999 |
| Malaika Enterprises Limited | Professional & scientific | 2018 |
| Malcolm V. Lelliott Limited | Professional & scientific | 2003 |
| Malden Bowling Green Company Limited(The) | Arts & recreation | 1919 |
| Maltascott Limited | Real estate | 1981 |
| MAM Holdings Ltd | Financial services | 2025 |
| Management Aids Limited | Professional & scientific | 2006 |
| Management Improvements Limited | Extraterritorial | 1986 |
| Management Networking Ltd | Education | 1998 |
| Managing Media Ltd. | Professional & scientific | 1999 |
| Managing Software Limited | Information & communication | 1997 |
| Manasi Software Solutions Ltd | Information & communication | 2016 |
| Manden Properties Limited | Construction | 1988 |
| Mane Department Limited | Wholesale & retail | 2025 |
| Mane Electrical Contractors Limited | Construction | 1999 |
| Mangamutu Limited | Professional & scientific | 1997 |
| Mango Tango Limited | Real estate | 2001 |
| Mani Chacko & Co Ltd | Professional & scientific | 2004 |
| Manor Bar & Grill Limited | Hospitality | 2024 |
| Manor of Bosham Limited | Extraterritorial | 1929 |
| Manor Way (Woking) LLP | | 2008 |
| Mansella Consulting Limited | Professional & scientific | 2008 |
| Manzana Business Solutions Limited | Administrative & support | 2004 |
| Mapilupe Holdings Limited | Real estate | 1981 |
| Maple Drive Lightwater (Management Company) Limited | Households | 2002 |
| Maple Fields (Llanrumney) Residents Management Company Limited | Households | 2024 |
| Maple Manor Home Ltd | Extraterritorial | 2019 |
| Maple Marine Ltd | Professional & scientific | 2007 |
| Maplehurst Close (Kingston) Management Company Limited | Real estate | 1984 |
| Mapu Property Limited | Real estate | 2024 |
| Marbletrack Enterprises Limited | Professional & scientific | 1984 |
| March & Stacey (Property) Limited | Real estate | 1951 |
| March Personnel Limited | Administrative & support | 2004 |
| Marchmont Holdings Limited | Wholesale & retail | 2016 |
| Marcola Computers Limited | Professional & scientific | 1986 |
| Marcus Developments International Limited | Real estate | 1972 |
| Mardec Joinery Limited | Manufacturing | 1992 |
| Marden Enterprises Limited | Hospitality | 1993 |
| Marelis Limited | Information & communication | 1999 |
| Margrasil U.K. Limited | Manufacturing | 2000 |
| Maria Hotels Ltd | Hospitality | 2023 |
| Maria Salon Ltd | Other services | 2024 |
| Marick Real Estate Ltd | Construction | 2014 |
| Marina Clinic Ltd | Health & social care | 2002 |
| Marinetech Partnership | | 1999 |
| Marjun Consulting Limited | Professional & scientific | 2001 |
| Mark & Young Industrial Supplies Ltd. | Professional & scientific | 2002 |
| Market Clarity Limited | Professional & scientific | 2003 |
| Marketing Innovations Limited | Professional & scientific | 1997 |
| Marko Creative Consultant Ltd | Administrative & support | 2016 |
| Markwick Limited | Professional & scientific | 1996 |
| Marlyn's House Limited | Households | 1995 |
| Marquis House PLC | | 1992 |
| Marrie-Jane AHB Ltd | Wholesale & retail | 2025 |
| Mars Global Investments Ltd | Real estate | 2022 |
| Marshall Music Tuition Limited | Education | 2003 |
| Martha Holding Limited | Professional & scientific | 2005 |
| Martin Cunningham Limited | Professional & scientific | 2003 |
| Martin James International Limited | Transport & logistics | 1991 |
| Martin Tiling Limited | Construction | 2007 |
| Martin Way Express Ltd | Wholesale & retail | 2025 |
| Masar UK Limited | Information & communication | 2003 |
| Mastercar Holdings Limited | Financial services | 2018 |
| Masterfold Limited | Wholesale & retail | 1987 |
| Mastery Academy for Training & Development Limited | Education | 2007 |
| Matco Properties Ltd | Real estate | 2023 |
| Matrics Limited | Extraterritorial | 1987 |
| Matrix Corporation UK Limited | Information & communication | 1995 |
| Matthew James Lettings Limited | Real estate | 2006 |
| Matthew Tatnell Limited | Administrative & support | 2002 |
| Matthews Taverns Limited | Hospitality | 1993 |
| Maule Property Developments Ltd | Administrative & support | 1967 |
| Maultway Management Company Limited(The) | Professional & scientific | 1985 |
| Maurico Hitchin Ltd | Wholesale & retail | 2026 |
| Mauripharm Limited | Wholesale & retail | 1995 |
| MAX Investments Ltd. | Hospitality | 2001 |
| Maxal Maritime Ltd | Administrative & support | 2010 |
| Maxbright Limited | Wholesale & retail | 2023 |
| Maximum Music Limited | Arts & recreation | 1992 |
| Maximum Songs Limited | Administrative & support | 1996 |
| Maxoil Services Limited | Mining & quarrying | 2007 |
| Maxsport Competition Tyres Limited | Wholesale & retail | 2002 |
| Maxwell Bathroom Specialists Limited | Wholesale & retail | 2003 |
| Maya Caring Ltd | Health & social care | 2023 |
| Mayfair Building Contractors Ltd | Other services | 2016 |
| Mayfield Hove Limited | Real estate | 2020 |
| Mayfield Investment Trust Limited | Real estate | 1938 |
| Mayfield Villages Care Limited | Health & social care | 2019 |
| Mayfield Villages Limited | Real estate | 2015 |
| Mayfields Ridgeway Management Limited | Households | 1988 |