| Mao's Chinese Medicine Ltd. | Health & social care | 2017 |
| Marguerite Consulting Limited | Administrative & support | 2019 |
| Mark and Daughters Limited | Real estate | 2024 |
| Mark Pinchin Painting & Decorating Limited | Construction | 2016 |
| Mark Wardle Ltd | Other services | 2004 |
| Mark Watkins Ltd | Professional & scientific | 2013 |
| Market Hall Retail Ltd | Wholesale & retail | 2024 |
| Market LUX Ltd | Construction | 2025 |
| Martells Limited | Financial services | 2021 |
| Martells of Sutton Limited | Wholesale & retail | 1939 |
| Martells Stores Limited | Administrative & support | 1949 |
| Martinez Enterprises Limited | Real estate | 2016 |
| Martinparbi Ltd | Wholesale & retail | 2019 |
| Martyns Place House Management Company Limited | Households | 1982 |
| Martyns Place Roads Management Company Limited | Households | 1982 |
| Marvesa UK Limited | Wholesale & retail | 2011 |
| Marysmagicshop Limited | Wholesale & retail | 2024 |
| Masaew Ltd | Financial services | 2024 |
| Mason & Beer LLP | | 2024 |
| Mason Bedford Ltd | Information & communication | 2018 |
| Masonry Clinic Ltd | Extraterritorial | 2024 |
| Master Cutters Limited | Other services | 2001 |
| Matrick Electrical Services Ltd | Construction | 2018 |
| Matt Newman Travel Ltd | Administrative & support | 2017 |
| Mavi INS UK Limited | Financial services | 2025 |
| Maxo Larna Consulting Ltd | Wholesale & retail | 2024 |
| Maxolarna Ltd | Wholesale & retail | 2022 |
| Mayavista Capital Ltd | Construction | 2025 |
| Mayhews Lettings Limited | Real estate | 2015 |
| Maynard Platinum Properties Limited | Construction | 2024 |
| Mbradford Holdings Ltd | Construction | 2016 |
| Mccance Holdings Limited | Financial services | 2020 |
| Mccance Ltd. | Health & social care | 2007 |
| Mccleans Landscapes Ltd | Administrative & support | 2024 |
| MCW Holdings Ltd | Financial services | 2025 |
| MD Mechanical Services Ltd | Construction | 2022 |
| ME Automated Flow International Ltd | Administrative & support | 2010 |
| Mead Place Ltd | Real estate | 2019 |
| Meadedge Limited | Information & communication | 2011 |
| Mechanicool Services Ltd | Energy | 2025 |
| Mecie Limited | Information & communication | 2022 |
| Medallion Arts Limited | Information & communication | 2022 |
| Medclear Limited | Water & waste | 2021 |
| Media Build Limited | Construction | 2022 |
| Media Hosting Ltd | Information & communication | 2015 |
| Medical Centre International Limited | Health & social care | 2003 |
| Medusa Luxury Ltd | Wholesale & retail | 2023 |
| Megabites Kebab Ltd | Hospitality | 2021 |
| Megalith Games Limited | Wholesale & retail | 2007 |
| Melchior Holdings Ltd | Real estate | 2020 |
| Melissa's Mega Manes Limited | Other services | 2021 |
| Membership Services Administration (U.K.) Limited | Administrative & support | 1993 |
| Meridian Carz Ltd | Transport & logistics | 2022 |
| Meridian Edge Ltd | Professional & scientific | 2025 |
| Meridian Finance Ltd | Extraterritorial | 2013 |
| Meridian Finance Partners Ltd | Other services | 2008 |
| Meridian FM Radio | Information & communication | 2008 |
| Meritorius Ltd | Construction | 2012 |
| Merlin Cleaning Services Ltd | Administrative & support | 2020 |
| Merranti Accounting (Brighton) Limited | Professional & scientific | 1996 |
| Merranti Accounting Limited | Professional & scientific | 2014 |
| Merranti Capital Limited | Financial services | 2015 |
| Merranti Figures Accounting Limited | Professional & scientific | 2022 |
| Merranti Ltd | Extraterritorial | 2014 |
| Merranti Recruitment Limited | Administrative & support | 2016 |
| Merrill Fraser Limited | Professional & scientific | 2017 |
| Mesto Consultants Ltd | Professional & scientific | 2014 |
| Metrostone Ltd | Real estate | 2023 |
| MG Perfect Renovation Ltd | Construction | 2024 |
| MGL Barber Ltd | Other services | 2023 |
| MID Sussex Windows Ltd | Construction | 2023 |
| Midrange Limited | Real estate | 1999 |
| Migr Ltd | Real estate | 2025 |
| Milantis Limited | Wholesale & retail | 2023 |
| Mill Cottages (East Grinstead) Limited | Households | 2005 |
| Millbell Property Limited | Real estate | 2017 |
| Miller Hub Limited | Wholesale & retail | 2012 |
| Miller Knight Limited | Financial services | 2004 |
| Millfield Close Residents Management Company Limited | Households | 2010 |
| Milton Business Services Limited | Professional & scientific | 2017 |
| Minexia Limited | Mining & quarrying | 2014 |
| Mini Notes Ltd | Administrative & support | 2020 |
| Minnerva Limited | Information & communication | 2000 |
| Miskaland Investment Group Ltd | Information & communication | 2019 |
| Miss Tidy Cleaningservices Ltd | Administrative & support | 2016 |
| Mitrestar Limited | Construction | 1999 |
| Mixed UP and Mixrace Limited | Wholesale & retail | 2024 |
| Mixedx Pictures Ltd | Information & communication | 2025 |
| MJ Country Lifestyle Ltd | Wholesale & retail | 2025 |
| MJA Planning and Development Ltd | Professional & scientific | 2020 |
| MJB Property Solutions Ltd | Construction | 2025 |
| MJW Design & Print Limited | Manufacturing | 2001 |
| MLT Trading Limited | Wholesale & retail | 2014 |
| Mmageek Consulting Limited | Information & communication | 2015 |
| Mmll Building & Investing Ltd | Construction | 2024 |
| Modac Properties Ltd | Real estate | 2025 |
| Mode Modular Sales Ltd | Construction | 2024 |
| Modern Life Financial Services Limited | Real estate | 2021 |
| Moles Groundworks Ltd | Administrative & support | 2018 |
| MON Monde Limited | Wholesale & retail | 2026 |