| M H Z Designs Limited | Information & communication | 1996 |
| M&Ms Consulting Limited | Professional & scientific | 2011 |
| M.B.O. (UK) Limited | Wholesale & retail | 1987 |
| M.C.D. Electrical Engineering Services Ltd | Construction | 2000 |
| M.C.G.Correspondence Colleges Limited | Education | 1955 |
| M.G. Wilson & Co Limited | Information & communication | 2001 |
| M.J. Burgess (Design) Limited | | 1981 |
| M.R.T Vehicle Solutions Ltd | Transport & logistics | 2023 |
| M.S.B. (Midland) Limited | | 1993 |
| M.W. Marketing Limited | Extraterritorial | 1990 |
| MA Motion Design Ltd | Professional & scientific | 2025 |
| MAC Merchant Limited | Wholesale & retail | 2000 |
| Macen-J Limited | Information & communication | 2019 |
| Mach Training Limited | | 2001 |
| Machx Limited | Professional & scientific | 2013 |
| Maes Therapy International Ltd | Education | 2025 |
| MAF Design Limited | Professional & scientific | 2004 |
| Magflo Products (Baldock) Limited | | 1983 |
| Magnet Applications Group Limited | Manufacturing | 2000 |
| Magog Industries Limited | Professional & scientific | 1990 |
| Magpie XR Limited | Information & communication | 2023 |
| Mahar Catering Group Ltd | Hospitality | 2023 |
| Mahone Bay Limited | Real estate | 2007 |
| Maia Management Consulting Ltd. | Information & communication | 2016 |
| Major Corporation Limited | Mining & quarrying | 2023 |
| Maka Holdings Limited | Real estate | 1987 |
| Makai Group Ltd | Wholesale & retail | 2022 |
| Mali Rentals Ltd | Transport & logistics | 2025 |
| Malthurst (UK) Limited | Professional & scientific | 1997 |
| Malthurst Anglia Limited | Real estate | 2015 |
| Malthurst Estates Limited | Real estate | 2012 |
| Malthurst Limited | Wholesale & retail | 1997 |
| Malthurst Petroleum Limited | Wholesale & retail | 1963 |
| Malthurst Retail Limited | Real estate | 1997 |
| Malthurst South East Limited | Real estate | 2015 |
| Mamco Consultants Limited | Construction | 2005 |
| Management and Economics Consultants International Limited | Professional & scientific | 1994 |
| Mandate Consultancy Limited | Professional & scientific | 2017 |
| Mangala Estates Limited | Real estate | 2025 |
| Manister Limited | Real estate | 1998 |
| Manor Service Stations Limited | Wholesale & retail | 1985 |
| Maphula Properties Limited | Real estate | 2021 |
| Marbles Design Limited | Professional & scientific | 1999 |
| Mardiquest Limited | Health & social care | 1985 |
| Maria Construction Limited | Construction | 2003 |
| Marisian Limited | Real estate | 2002 |
| Marius Iacob Limited | Construction | 2016 |
| Mark Griffiths Plumbing & Heating Limited | Construction | 2002 |
| Markakis Limited | Real estate | 1982 |
| Market Enterprize Limited | Wholesale & retail | 1963 |
| Market Focus Consulting Limited | Administrative & support | 2007 |
| Marketing Message Limited | Professional & scientific | 2005 |
| Marketing Support International Limited | Administrative & support | 1993 |
| Markham & Marsden Limited | Administrative & support | 2003 |
| Markwell Glass Limited | Construction | 1995 |
| Marmaris Turkish Restaurant Limited | Hospitality | 2020 |
| Marshgate Works Management Limited | Households | 1995 |
| Martyn R Brown Consulting Ltd | Administrative & support | 2016 |
| Marvel Property Developments Ltd | Real estate | 2022 |
| Marvel Property Group Ltd | Real estate | 2012 |
| Massif Technology Limited | Arts & recreation | 1996 |
| Master Computer Services Limited | Other services | 1998 |
| Mastercars (Biggleswade) Limited | Wholesale & retail | 2008 |
| Masterlay Brick Company Limited | Construction | 2003 |
| Masters Brothers(Fuels)Limited | Education | 1960 |
| Matchcost Limited | Construction | 1991 |
| Materials Technology Consultants Limited | Professional & scientific | 1974 |
| Matt Hember Limited | Information & communication | 2000 |
| Matters Financial Limited | Professional & scientific | 1998 |
| MAX Branding Ltd | Transport & logistics | 2006 |
| Maxim Barbershop Ltd | Other services | 2019 |
| Maxxisaver UK Limited | Other services | 2025 |
| Maya ARK Limited | Wholesale & retail | 2024 |
| Mayhall Properties Limited | Real estate | 1996 |
| Maymana Market Ltd | Wholesale & retail | 2020 |
| Mbda UK Limited | Manufacturing | 1996 |
| Mbda UK Sports and Social Club Limited | Other services | 2001 |
| Mcdermot & Co | | 1989 |
| Medgold Limited | Construction | 2005 |
| Media&Leads Ltd | Professional & scientific | 2015 |
| Mediasplash Limited | Professional & scientific | 2000 |
| Medipin Limited | Manufacturing | 2003 |
| Medlock Electric Limited | Extraterritorial | 1977 |
| Medlock Electrical Distributors Limited | Wholesale & retail | 1947 |
| Medsurge Healthcare UK Ltd | Wholesale & retail | 2022 |
| Meekley and Sarge Limited | Hospitality | 2004 |
| Mehmet Mustafa Limited | Transport & logistics | 2010 |
| Melesey Limited | Professional & scientific | 2000 |
| Melissa Electrical Distributors Ltd | Wholesale & retail | 2003 |
| Melrose Place Management Company (NO.3) Limited | Households | 1991 |
| Menace Management Limited | Information & communication | 1988 |
| Menace Music Limited | Information & communication | 1988 |
| Mentek-It Ltd | Information & communication | 2025 |
| Mentor Publicity Limited | Professional & scientific | 1966 |
| Mentor Services (Stevenage) Limited | Real estate | 2007 |
| Mentor Services Limited | Real estate | 1984 |
| Meraki Studios London Ltd | Professional & scientific | 2022 |
| Mercer & Hole Trustees Limited | Administrative & support | 1996 |
| Mercuri International UK Consulting Ltd | Professional & scientific | 2022 |
| Mercury Challenger Bidco Limited | Professional & scientific | 2024 |