| MCM Contract Mowing & Grounds Maintenance Ltd | Administrative & support | 2015 |
| MCN Print Media Limited | Manufacturing | 2014 |
| Mcsd Aberdeen Ltd | Administrative & support | 2022 |
| MD Enterprise Retail Limited | Wholesale & retail | 2020 |
| MD2 Recruitment Ltd | Administrative & support | 2025 |
| MDA Car Traders Ltd | Wholesale & retail | 2025 |
| Mdaf Construction Limited | Construction | 2024 |
| MDC Accounting Services Ltd | Professional & scientific | 2013 |
| MDF Property Management Limited | Real estate | 2005 |
| MDM Software Limited | Information & communication | 2023 |
| MDM Talent Management Ltd | Professional & scientific | 2015 |
| Mdprocurementconsulting Limited | Professional & scientific | 2017 |
| Mdrag Transport Ltd | Transport & logistics | 2026 |
| MDS Alignment Limited | Professional & scientific | 2023 |
| ME + LI Ltd | Other services | 2024 |
| ME3KINS Pokemon Ltd | Wholesale & retail | 2025 |
| ME3KINS TCC Ltd | Wholesale & retail | 2024 |
| Meadow Mobility Ltd | Wholesale & retail | 2001 |
| Meadow View (Ongar) Residents Company Limited | Households | 2010 |
| Meadow View (Rotherham) Management Company Limited | Households | 2009 |
| Meadow View Silver END Estate Management Company Limited | Households | 2019 |
| Meadowcroft (Bowes Road) Management Company Limited | Households | 2010 |
| Meadows (Hillingdon) Management Company Limited | Households | 1986 |
| Mechanical Installation Consultancy Services Limited | Construction | 2012 |
| MECHANIX2YOU Ltd | Wholesale & retail | 2022 |
| MED Sales Academy Group Limited | Administrative & support | 2020 |
| Medcoachuk Ltd | Professional & scientific | 2014 |
| Medgo Limited | Hospitality | 2003 |
| Medgobricks Limited | Real estate | 2025 |
| Medi-Teknique Limited | Manufacturing | 2013 |
| Medical Imaging UK Limited | Health & social care | 2002 |
| Medite Card Ltd | Other services | 2020 |
| Medray (UK) Limited | Other services | 2019 |
| Megafour Holdings UK Ltd | Construction | 2024 |
| Megan Associates Limited | Other services | 2020 |
| Megan Subsidiary Associates Limited | Other services | 2025 |
| Meganexus Ltd | Information & communication | 1998 |
| Meggitt (Canford) Limited | Extraterritorial | 1981 |
| Meggitt (Colehill) Limited | Extraterritorial | 1994 |
| Meggitt (Korea) Limited | Professional & scientific | 1995 |
| Meggitt (Pamphill) Limited | Extraterritorial | 1971 |
| Meggitt (Sapphire) Limited | Extraterritorial | 1986 |
| Meggitt (Shapwick) Limited | Extraterritorial | 1990 |
| Meggitt (Tarrant) Limited | Extraterritorial | 1911 |
| Meggitt (Wimborne) Limited | Extraterritorial | 1957 |
| Meggitt Acquisition Limited | Professional & scientific | 1986 |
| Meggitt Advanced Composites Limited | Professional & scientific | 1999 |
| Meggitt Aerospace Holdings Limited | Professional & scientific | 1998 |
| Meggitt Engineering Limited | Extraterritorial | 1958 |
| Meggitt Filtration & Transfer Limited | Extraterritorial | 1982 |
| Meggitt Finance Limited | Financial services | 2011 |
| Meggitt International Holdings Limited | Professional & scientific | 2011 |
| Meggitt International Limited | Professional & scientific | 1992 |
| Meggitt Investments Limited | Professional & scientific | 1992 |
| Meggitt Pension Plan Trustees Limited | Financial services | 1999 |
| Meggitt Pension Trust Limited | Extraterritorial | 1977 |
| Meggitt Properties Limited | Real estate | 1929 |
| Megta Ltd | Administrative & support | 2024 |
| Mehm Project Services Ltd | Professional & scientific | 2018 |
| Meiw Limited | Construction | 2025 |
| Melford Court Residents Association Limited | Households | 1993 |
| Melhold Limited | Extraterritorial | 2015 |
| Melina Group Limited | Construction | 1962 |
| Mellis Blue Limited | Administrative & support | 2007 |
| Mello Maid (Hemel Hempstead) Ltd | Other services | 2009 |
| Melt Media Group Ltd | Professional & scientific | 2026 |
| Melt PR Limited | Professional & scientific | 2018 |
| Melwoods Accountancy Services Limited | Professional & scientific | 1995 |
| Melwoods Management Services (1001) Ltd | Professional & scientific | 2003 |
| MEMETCAN27 Ltd | Other services | 2025 |
| Memoire Ltd | Professional & scientific | 2025 |
| Menage Pantano Limited | Wholesale & retail | 2016 |
| Mental Break Apparel Ltd | Wholesale & retail | 2025 |
| Mentmore Power Services Limited | Construction | 2017 |
| Menyah Ltd | Administrative & support | 2019 |
| Merchant's Mark Ltd | Wholesale & retail | 2023 |
| Merchndice Ltd | Wholesale & retail | 2026 |
| Mercury Consultants Limited | Professional & scientific | 2019 |
| Merriman Brothers Limited | Construction | 2012 |
| Mersea Island Holiday Park Limited | Hospitality | 2010 |
| Merton and SON Company Ltd | Construction | 2024 |
| Meru Holdings Limited | Extraterritorial | 2025 |
| Merz Aesthetics UK Limited | Wholesale & retail | 2022 |
| Merz Pharma UK Limited | Wholesale & retail | 2003 |
| Metacode Ltd | Information & communication | 2015 |
| Metafit Training Limited | Arts & recreation | 2011 |
| Metatron K9 Guarding Ltd | Administrative & support | 2020 |
| Metelec Services Ltd | Construction | 2017 |
| Methi Apsley Ltd | Hospitality | 2026 |
| Method Land Limited | Real estate | 2021 |
| Metis LAB Ltd | Professional & scientific | 2025 |
| Metro Assets Limited | Professional & scientific | 2018 |
| Metro City Holdings Limited | Real estate | 2021 |
| Metro Equities Limited | Financial services | 2013 |
| MEX Tortilla Limited | Manufacturing | 2023 |
| MEX Trading Ltd | Wholesale & retail | 2009 |
| Mexgrocer Limited | Hospitality | 2012 |
| Mezza Brands Ltd | Professional & scientific | 2023 |
| Mezzo Management Company (Somerset) Limited | Households | 2010 |
| MFG London Ltd | Health & social care | 2024 |