| Master EYE Ltd | Administrative & support | 2026 |
| Master Payroll Ltd | Construction | 2019 |
| Masterheat (Luton) Limited | | 1985 |
| Mastersons Properties Limited | Real estate | 2004 |
| Masti Night Limited | Hospitality | 2025 |
| Matchstat Ltd | Information & communication | 2014 |
| Matemil Ltd | Extraterritorial | 2021 |
| Mathemagicians Limited | Education | 2017 |
| Matrix Development - SPV2 Ltd | Real estate | 2018 |
| Matrix Holdco Ltd | Households | 2019 |
| Matt Timmis International Limited | Transport & logistics | 2011 |
| Matterhorn Asset Management Limited | Real estate | 2016 |
| Maun Investments Limited | Professional & scientific | 2014 |
| Maun Properties Limited | Real estate | 2015 |
| Maven Catalyst Ltd | Professional & scientific | 2026 |
| Maverick Consultant Ltd | Professional & scientific | 2017 |
| Maverick Moves Limited | Wholesale & retail | 2022 |
| MAX Biotech Limited | Professional & scientific | 2019 |
| MAX Biotech Subco Limited | Professional & scientific | 2023 |
| MAX Cleaning Ltd | Administrative & support | 2024 |
| MAX Enterprise Ltd | Professional & scientific | 2007 |
| MAX Property Services Ltd | Construction | 2019 |
| Maxpro Global Limited | Professional & scientific | 2023 |
| Maxradiance Limited | Professional & scientific | 2020 |
| Maxwell & Morton Limited | Arts & recreation | 2021 |
| Maxworld Ltd | Information & communication | 2025 |
| Maya Pharmacare Limited | Health & social care | 2017 |
| Mayfair Medical Practice Ltd | Health & social care | 2024 |
| Mayjoo Limited | Real estate | 2025 |
| Mayo GAS Plumbing & Heating Ltd | Construction | 2014 |
| Mayobridge Holdings LLP | | 2022 |
| Maytree Grounds & Gardens Ltd | Administrative & support | 2026 |
| MB Medical London Ltd | Health & social care | 2024 |
| MBA Property Holdings Limited | Real estate | 2024 |
| MBL Architecture Ltd | Professional & scientific | 2022 |
| MBL Property Development Ltd | Real estate | 2024 |
| Mblord Limited | Wholesale & retail | 2023 |
| MBR Property Consulting Ltd | Households | 2024 |
| MBR Talent Consulting Ltd | Administrative & support | 2020 |
| MBS Wholesale Limited | Wholesale & retail | 2003 |
| MBS Wholesale Supplies Limited | Financial services | 2023 |
| MC Unisex Salon Ltd | Other services | 2025 |
| Mcac Properties Limited | Hospitality | 2024 |
| Mcandrew Family Partnership LLP | | 2022 |
| MCB Trading Enterprise Ltd | Construction | 2021 |
| Mccabe Property Services Ltd | Real estate | 2020 |
| Mccanns HRC Limited | Professional & scientific | 2003 |
| Mcdermott Property Maintenance Ltd | Construction | 2026 |
| Mcgarvey Kearns Ltd | Real estate | 2022 |
| Mcgrill & Forbes Ltd | Information & communication | 2006 |
| Mckore Group Ltd | Households | 2024 |
| Mcmahon Commercial Properties Ltd | Construction | 2021 |
| MCP Document Solutions Limited | Extraterritorial | 2020 |
| MCV Global Limited | Wholesale & retail | 2022 |
| MCV Holdco Limited | Real estate | 2025 |
| MD Payroll Ltd | Administrative & support | 2022 |
| MD2U Limited | Extraterritorial | 2012 |
| MDA Wellness Holdings Ltd | Financial services | 2026 |
| Mdjd Limited | Hospitality | 2017 |
| MDP Healthcare Ltd | Professional & scientific | 2015 |
| MDPVT001 Ltd | Real estate | 2017 |
| MDPVT002 Ltd | Real estate | 2017 |
| MDPVT003 Ltd | Real estate | 2017 |
| Mdtex Agency Limited | Wholesale & retail | 2002 |
| MDW Carpentry Limited | Manufacturing | 2025 |
| Meanmods Ltd | Professional & scientific | 2025 |
| Meatland Supplies Limited | Wholesale & retail | 2010 |
| Mech Power Ltd | Wholesale & retail | 2020 |
| MED Zone Limited | Wholesale & retail | 2021 |
| Medchoice Ltd | Health & social care | 2011 |
| Medcomms London Ltd | Professional & scientific | 2026 |
| Medgate Prime Ltd | Wholesale & retail | 2023 |
| Media Darling Ltd | Information & communication | 2008 |
| Media Web Solutions Limited | Information & communication | 2013 |
| Medialloys UK Ltd | Wholesale & retail | 2025 |
| Medical and Surgical Urology Ltd | Health & social care | 2015 |
| Medicalis Ltd | Health & social care | 2012 |
| Medicean Limited | Other services | 2006 |
| Medicines 4 U Ltd | Wholesale & retail | 2005 |
| Medicines Direct Limited | Real estate | 2012 |
| Medicines Plus Limited | Wholesale & retail | 2013 |
| Mediclerxx Ltd | Administrative & support | 2024 |
| Medihealth (UK) Ltd | Health & social care | 2007 |
| Medihealthrx Ltd | Health & social care | 2022 |
| Mediken Limited | Financial services | 2024 |
| Medipharm Pro Limited | Wholesale & retail | 2024 |
| Medpar Limited | Health & social care | 2019 |
| Medrec Global Ltd | Administrative & support | 2020 |
| Medsales Management Consulting Ltd | Professional & scientific | 2025 |
| Medways Cash and Carry Limited | Wholesale & retail | 2008 |
| Meedivko Savouries Limited | Manufacturing | 2010 |
| Meesha Enterprise Limited | Wholesale & retail | 2026 |
| Megha Eshop Limited | Wholesale & retail | 2025 |
| Meghu Ltd | Wholesale & retail | 2024 |
| Megosa Ltd | Wholesale & retail | 2020 |
| Mehara Collections Ltd | Wholesale & retail | 2024 |
| Mehdip Estate Ltd | Financial services | 2019 |
| MEK Barbers Ltd | Other services | 2021 |
| Mellor Consultants Ltd | Professional & scientific | 2023 |
| Melodian Limited | Information & communication | 2003 |