| Maple Yard Limited | Real estate | 2025 |
| Mapped Recruitment Ltd | Administrative & support | 2020 |
| Maragh Refurbishments Ltd | Construction | 2024 |
| Maramures Shop Ltd | Wholesale & retail | 2018 |
| Marie and More Limited | Real estate | 2019 |
| Mariella Limited | Wholesale & retail | 2025 |
| Marija Vella - Psychologist in Psychotherapy Limited | Health & social care | 2017 |
| Mario Luxe Detail Ltd | Administrative & support | 2025 |
| Mark Haylock Limited | Professional & scientific | 2007 |
| Marketly Ltd | Construction | 2013 |
| Markplane Property Limited | Real estate | 2017 |
| Marley Fitting Services Ltd | Construction | 2025 |
| Marley Flooring Ltd | Construction | 2024 |
| Marlora Properties Limited | Real estate | 2025 |
| Marr SPV Ltd | Real estate | 2025 |
| Mars Building Group Ltd | Construction | 2021 |
| Marsden Mineral Services Limited | Professional & scientific | 2013 |
| Marsh & Sons Limited | Extraterritorial | 1997 |
| Marsh & Sons Properties Limited | Extraterritorial | 2001 |
| Martini Associates Limited | Construction | 2016 |
| Martini Holdings Limited | Real estate | 2025 |
| Martini Maintenance Services Limited | Construction | 2023 |
| Martyr Apparel Ltd | Wholesale & retail | 2024 |
| Marvellous Trims Limited | Other services | 2025 |
| Marvin Herbert Projects CIC | Education | 2025 |
| Marz Holdings Ltd | Financial services | 2024 |
| MAS Cleaning Solutions Ltd | Households | 2021 |
| Masal Limited | Wholesale & retail | 2011 |
| Masala Chutney Limited | Hospitality | 2025 |
| Mask Investments Ltd | Financial services | 2020 |
| Mass Electrical Solutions Limited | Construction | 2023 |
| Mater LAI Ltd | Real estate | 2025 |
| Materia Design Studio Ltd | Construction | 2026 |
| Matricmax Consultants Limited | Information & communication | 2025 |
| Mattboat Trading Ltd | Wholesale & retail | 2023 |
| Matthew Jenkins Limited | Health & social care | 2016 |
| Matthews Property Holdings Ltd | Real estate | 2020 |
| Maverick Strength Coaching Ltd | Health & social care | 2022 |
| Mavrck Gym Ltd | Arts & recreation | 2023 |
| Mavrck Holdings Ltd | Arts & recreation | 2017 |
| Mawc Digital Consulting Ltd | Arts & recreation | 2024 |
| Mawskyfit Ltd | Arts & recreation | 2026 |
| Maximus Protection Services Ltd | Administrative & support | 2008 |
| Maxy Cash & Carry Limited | Wholesale & retail | 2016 |
| Mayfair Digital Agency Ltd | Wholesale & retail | 2026 |
| Mayfair TV Series Ltd | Information & communication | 2025 |
| Maynard Court Limited | Health & social care | 2020 |
| Mazatec Ltd | Wholesale & retail | 2025 |
| Mbpl Utilities Ltd | Professional & scientific | 2022 |
| MBS Solutions International Ltd | Construction | 2020 |
| MC Academy Ltd | Other services | 2023 |
| MC VIP Cars Ltd | Transport & logistics | 2024 |
| MC VIP Ltd | Transport & logistics | 2025 |
| MC Waste OIL Limited | Water & waste | 2022 |
| Mcdaniel Stoneworks Limited | Administrative & support | 2026 |
| Mchardy Real Estate Limited | Real estate | 2013 |
| Mcintosh Residential Surveys Ltd | Professional & scientific | 2021 |
| MCK London Florist Limited | Wholesale & retail | 2026 |
| Mckenzie Group Ltd | Real estate | 2025 |
| Mckenzie Holdings Ltd | Extraterritorial | 2020 |
| MCM Design Limited | Extraterritorial | 2010 |
| MCM Electrical Ltd | Energy | 2018 |
| MCM Property Group Ltd | Real estate | 2019 |
| Mcmurray Holdings Limited | Professional & scientific | 2023 |
| MCN Holdings Ltd | Real estate | 2025 |
| Mcnorton Property Group Limited | Real estate | 2025 |
| MCS Solar Power Ltd | Construction | 2024 |
| MD Fire & Security LLP | | 2019 |
| Mdab Properties UK Limited | Real estate | 2022 |
| Mdal Consulting Limited | Construction | 2025 |
| MDK Property Limited | Real estate | 2026 |
| Meadows 24 Limited | Hospitality | 2024 |
| Meat Corporation of Namibia (UK) Limited | Wholesale & retail | 1990 |
| Meat Republic Ltd | Wholesale & retail | 2021 |
| Mecon Steel Products Limited | Manufacturing | 1967 |
| Medcare Plus Limited | Wholesale & retail | 2019 |
| Medcoast Supplies UK Ltd | Wholesale & retail | 2020 |
| Mediatown Community CIC | Information & communication | 2025 |
| Medics DUO Limited | Education | 2024 |
| Meera UK Holdings Ltd | Real estate | 2025 |
| Meere Property Ltd | Real estate | 2024 |
| Mefs Services Ltd | Administrative & support | 2022 |
| Mega Design and Build Ltd | Construction | 2022 |
| Megascott Limited | Administrative & support | 2014 |
| Megax Construction and Consultancy Ltd | Construction | 2021 |
| MEJ Enterprises Ltd | Real estate | 2022 |
| Melbond Limited | Real estate | 2003 |
| Meldrum Properties Limited | Professional & scientific | 1999 |
| Meleray Consultancy Ltd | Professional & scientific | 2025 |
| Meli Publishing Limited | Information & communication | 2019 |
| Meliora High School Ltd | Education | 2023 |
| Melissa Properties Ltd | Real estate | 2025 |
| MEM Interiors Limited | Administrative & support | 2015 |
| Memo Ltd | Wholesale & retail | 2024 |
| Memories Online Limited | Real estate | 2015 |
| Mensoul Retreat Ltd | Wholesale & retail | 2026 |
| Mental Health Wellbeing Foundation CIC | Education | 2023 |
| Mentor Services (Storage) Limited | Real estate | 2017 |
| Mentor Services HRB Limited | Real estate | 2026 |
| Menya & Co Limited | Health & social care | 2016 |