| MBC11 Services Ltd | Arts & recreation | 2003 |
| MBD Foods Limited | Manufacturing | 1994 |
| Mbdn Langley Ltd | Administrative & support | 2021 |
| MBE Property Management Ltd | Real estate | 2024 |
| MBI Cars Limited | Transport & logistics | 2025 |
| MC Racecourses Limited | Arts & recreation | 2011 |
| MC Racetracks Limited | Arts & recreation | 2011 |
| MC Square Consultants Ltd | Professional & scientific | 2024 |
| MC2 Electrical Services Limited | Manufacturing | 2023 |
| MCA Developments Limited | Extraterritorial | 1985 |
| MCA Drylining Services Limited | Construction | 2016 |
| MCA East Limited | Extraterritorial | 1937 |
| MCA Holdings Limited | Extraterritorial | 1973 |
| MCA Land Limited | Extraterritorial | 1963 |
| MCA Leicester Limited | Extraterritorial | 1963 |
| MCA London Limited | Extraterritorial | 1976 |
| MCA Northumbria Limited | Extraterritorial | 1972 |
| MCA Partnership Housing Limited | Extraterritorial | 1994 |
| MCA Social Club Ltd | Hospitality | 2026 |
| MCA South West Limited | Extraterritorial | 1971 |
| MCA West Midlands Limited | Extraterritorial | 1968 |
| MCA Yorkshire Limited | Extraterritorial | 1954 |
| Mcculloch&Co Ltd | Construction | 2023 |
| Mcdrail Limited | Construction | 2014 |
| Mcentyre Holdings Limited | Real estate | 2016 |
| Mcentyre Property Ltd | Real estate | 2025 |
| Mcewen Design Services Ltd | Professional & scientific | 2023 |
| Mcggc Limited | Information & communication | 2026 |
| MCH Trading Ltd | Wholesale & retail | 2025 |
| MCK Supermarket Ltd | Wholesale & retail | 2016 |
| Mckay Management LLP | | 2012 |
| Mckay Management Partner Limited | Extraterritorial | 2012 |
| Mcks Inner Studies UK & Ireland Ltd | Other services | 2013 |
| Mclean Homes Bristol & West Limited | Extraterritorial | 1967 |
| Mclean Homes Limited | Professional & scientific | 1932 |
| Mclean Homes Southern Limited | Extraterritorial | 1963 |
| Mclean TW (Chester) Limited | Extraterritorial | 1972 |
| Mclean TW (Northern) Limited | Extraterritorial | 1972 |
| Mclean TW (Southern) Limited | Extraterritorial | 1990 |
| Mclean TW (Yorkshire) Limited | Extraterritorial | 1990 |
| Mclean TW Estates Limited | Extraterritorial | 1999 |
| Mclean TW Group Limited | Extraterritorial | 1987 |
| Mclean TW Holdings Limited | Extraterritorial | 2001 |
| Mclean TW Limited | Extraterritorial | 1986 |
| Mclean TW NO.2 Limited | Extraterritorial | 1998 |
| Mclouis Distilleries Limited | Manufacturing | 2024 |
| MCO Cars Ltd | Wholesale & retail | 2025 |
| MCR Commissioning Limited | Construction | 2013 |
| MCS Professional Services Ltd | Information & communication | 2014 |
| Mcsweeney Consultancy Ltd | Other services | 2016 |
| Mcvr G83 & G84 Ltd | Administrative & support | 2025 |
| Mcvr Ltd | Wholesale & retail | 2023 |
| MD3 Consulting Limited | Other services | 2019 |
| MDA Plumbing and Heating Limited | Construction | 2018 |
| MDH Group Holdings Ltd | Wholesale & retail | 2023 |
| Mdizeno Ltd | Wholesale & retail | 2019 |
| Mdlx Ltd | Arts & recreation | 2024 |
| Mead Business Centre Limited | Real estate | 2004 |
| Meadow View LH Limited | Construction | 2021 |
| Meatwala Group Ltd | Wholesale & retail | 2023 |
| Mecasa Homes Ltd | Real estate | 2026 |
| Mechtech Facilities Services Ltd | Professional & scientific | 2024 |
| MED Legal Limited | Professional & scientific | 2025 |
| Medcuris Ltd | Health & social care | 2023 |
| Medelevate Limited | Public administration | 2025 |
| Medford’S Property Maintenance Ltd | Construction | 2023 |
| Media 4 Retail Limited | Administrative & support | 2020 |
| Media Transport Ltd | Transport & logistics | 2017 |
| Mediamiracle Solutions Ltd | Professional & scientific | 2024 |
| Mediation Buckinghamshire | Other services | 2002 |
| Medicals Healthcare Limited | Health & social care | 2014 |
| Medicy Pharma Limited | Wholesale & retail | 2022 |
| Medident Clinic Ltd | Information & communication | 2025 |
| Mediplus Holdings Limited | Administrative & support | 2021 |
| Mediplus Limited | Manufacturing | 1986 |
| Mediprod Limited | Extraterritorial | 2020 |
| Medipros Recruitment Limited | Administrative & support | 2025 |
| Mediwrite Limited | Professional & scientific | 2011 |
| Medled Ltd | Education | 2017 |
| Medlin With Paint Ltd | Construction | 2012 |
| Mednov Ltd | Other services | 2026 |
| Medtech Marketing Limited | Professional & scientific | 2014 |
| Meechanomics Ltd | Professional & scientific | 2007 |
| Mega BM Ltd | Transport & logistics | 2024 |
| Mega Image Print Production Limited | Manufacturing | 2015 |
| Megelli Publishing Limited | Information & communication | 2025 |
| Mehcatering Limited | Hospitality | 2020 |
| Mehfil Ltd | Real estate | 2019 |
| Mehndi Limited | Hospitality | 2025 |
| Mekong Travel Limited | Wholesale & retail | 2000 |
| Mela Creative Limited | Administrative & support | 2015 |
| Melbourne Investments Limited | Extraterritorial | 1968 |
| Melchoir Limited | Health & social care | 2016 |
| Melongrab Ltd | Professional & scientific | 2020 |
| MEN With Machines CIC | Administrative & support | 2023 |
| Menarini Stemline U.K. Limited | Wholesale & retail | 1998 |
| MEO Foods Ltd | Hospitality | 2021 |
| MER Professional Ltd | Other services | 2020 |
| Mercedez Group Limited | Real estate | 2001 |
| Mercedez Limited | Other services | 2004 |