| Merseyside Roofcare Limited | Construction | 2026 |
| Metrobank Consulting Ltd | Administrative & support | 2003 |
| MG Scaffolding (Oxford) Limited | Construction | 2002 |
| MI Market Ltd | Wholesale & retail | 2021 |
| MIA Rail Limited | Construction | 2014 |
| Mica IT Ltd | Information & communication | 2007 |
| Michael Baddeley Transport Limited | Wholesale & retail | 1978 |
| Michael Houston Railway Services Limited | Professional & scientific | 2016 |
| Michala Potts Ltd | Other services | 2008 |
| Michelangelos Restaurant (Buxton) Limited | Hospitality | 2004 |
| Mick Barrett Racing Limited | Arts & recreation | 2002 |
| Microvell Networks Ltd | Information & communication | 2003 |
| Midas Engineering Supplies Ltd | Wholesale & retail | 2001 |
| Mightyeagle UK Ltd | Wholesale & retail | 2016 |
| Mike Penney Limited | Construction | 1999 |
| Milan Global Ltd | Real estate | 2024 |
| Miles Macadam Construction Ltd | Administrative & support | 1970 |
| Miles Macadam Limited | Construction | 1995 |
| Miles Macadam Manufacturing Limited | Manufacturing | 1997 |
| Miles Macadam Products Limited | Extraterritorial | 1988 |
| Miles Macadam Surfacing Limited | Extraterritorial | 1986 |
| Miles-Ollerhead Limited | Professional & scientific | 1996 |
| Milestone Communications Limited | Information & communication | 2005 |
| Mill Trading (Middlewich) Limited | Manufacturing | 2010 |
| Millennium Mortgage Centre Ltd | Financial services | 2003 |
| Millwood Packaging Specialists Limited | Real estate | 2021 |
| Miltec Limited | Information & communication | 1998 |
| Mimaki (UK) Limited | Extraterritorial | 1997 |
| Minisoils Limited | Administrative & support | 2007 |
| Miparg Properties Ltd | Real estate | 2021 |
| Miquill Catering Limited | Hospitality | 2009 |
| Mirza Ahmed Medical Services Ltd | Health & social care | 2007 |
| Mitten Asbestos Ltd | Construction | 2019 |
| MIX UK Limited | Manufacturing | 1998 |
| MJB Technical Solutions Limited | Transport & logistics | 2003 |
| MJC Light Industrial Limited | Professional & scientific | 2007 |
| MJM Fencing Limited | Wholesale & retail | 2006 |
| MJN Radiology Ltd | Health & social care | 2023 |
| MK Scoular Limited | Real estate | 2006 |
| MMI Properties (Wilmslow) Limited | Real estate | 1986 |
| Mode Hair Salon Limited | Other services | 2006 |
| MODE2 Limited | Information & communication | 2004 |
| Modulus Development Limited | Financial services | 2007 |
| Modulus Management Consultancy Limited | Information & communication | 1987 |
| Molliebod Properties Ltd | Real estate | 2019 |
| Mollington Consultants Limited | Information & communication | 2005 |
| Molloy Lifting Limited | Administrative & support | 2007 |
| Monarch Fitted Interiors Limited | Wholesale & retail | 2018 |
| Mondiale Technology Media Limited | Information & communication | 2015 |
| Mondo Stadia Media Limited | Information & communication | 2021 |
| Moneypoint Finance Limited | Financial services | 1991 |
| Monsta Limited | Professional & scientific | 2007 |
| Moonvale Limited | Real estate | 1975 |
| Moor Electricians Limited | Construction | 2006 |
| Moore Accountancy Limited | Professional & scientific | 2002 |
| Moorland Adventure Limited | Arts & recreation | 1994 |
| Moors Andrew Thomas & Co Limited Liability Partnership | | 2002 |
| Moors, Andrew Thomas (Private Clients) Limited | Professional & scientific | 2004 |
| Morgman Medical Limited | Health & social care | 2017 |
| Mornflake Energy Limited | Energy | 1991 |
| Morris Homes (Eastern) Limited | Construction | 1988 |
| Morton Security (North West) Limited | | 1983 |
| Morton's Solicitors Limited | Professional & scientific | 2004 |
| Motor Bodies Widnes Limited | Wholesale & retail | 1999 |
| Motorsport (U.K.) Limited | Extraterritorial | 1991 |
| Mount Pleasant (Glazebrook) Residents Management Company Limited | Households | 2024 |
| Mountlands Trust Limited | Health & social care | 1937 |
| MP Flanagan Joiner (Builder) Ltd | Construction | 2001 |
| MPR 2023 Ltd | Health & social care | 2023 |
| MRD Services Macclesfield Limited | Construction | 2006 |
| MSS Consulting Limited | Professional & scientific | 2005 |
| MSS Environmental Ltd | Water & waste | 2005 |
| MSS Facilities Services Ltd | Administrative & support | 2005 |
| MSS Group Limited | Administrative & support | 2005 |
| MSS Water Limited | Manufacturing | 2002 |
| Msse Ltd | Professional & scientific | 2010 |
| Mssj Limited | Real estate | 2005 |
| MTE Meter Test Equipment (UK) Limited | Administrative & support | 1961 |
| MTG Global (MFG) Ltd | Manufacturing | 2024 |
| Multifit Wellness Limited | Arts & recreation | 2017 |
| Multistar Leasing Limited | Administrative & support | 2004 |
| Murray Contracting Limited | Administrative & support | 2004 |
| Murraywood Construction Limited | Construction | 1996 |
| Musicworks (UK) Limited | Manufacturing | 1999 |
| Musketeer Properties Limited | Real estate | 1998 |
| Mvmr Limited | Professional & scientific | 2006 |
| MW Machines 4X4 Limited | Wholesale & retail | 2021 |
| MWH Constructors Limited | Construction | 2018 |
| MWH Farrer Limited | Professional & scientific | 2006 |
| MWH Limited | Construction | 2018 |
| MWH Treatment Limited | Construction | 1980 |
| MWH UK Acquisitions Limited | Construction | 2018 |
| MWM Property Limited | Real estate | 2006 |
| My Playlist Limited | Real estate | 2007 |
| Myfallback Company Limited | Information & communication | 2007 |
| Myprovide Limited | Health & social care | 2023 |
| Mypura.Com Group Limited | Financial services | 2021 |
| Mypura.Com Limited | Wholesale & retail | 2019 |
| Mémoire Beauty Ltd | Manufacturing | 2020 |
| N and N Matthews Limited | Agriculture & fishing | 2007 |