| Marquee Moon Limited | Arts & recreation | 2008 |
| Marques Consultancy Limited | Professional & scientific | 2023 |
| Marquess Property Ltd | Real estate | 2020 |
| Marrcopolls Transport Limited | Transport & logistics | 2019 |
| Marriott and Marriott Limited | Information & communication | 2012 |
| Marriott Gibbs Rees Wallis Limited | Professional & scientific | 2000 |
| Marriott Plumbing & Heating Limited | Construction | 2003 |
| Marriott Ventures Ltd | Administrative & support | 2025 |
| Mars International Foods & Drinks Limited | Wholesale & retail | 2024 |
| Marsdens Farms Limited | Agriculture & fishing | 2007 |
| Marsdens Property Investments Limited | Extraterritorial | 2012 |
| Marsh & Co. Holdings Ltd | Manufacturing | 2018 |
| Marsh Auto Parts Limited | Wholesale & retail | 2013 |
| Marsh House Financial Services Limited | Financial services | 2003 |
| Marsh Paving & Landscaping Ltd | Construction | 2016 |
| Marsh Valley Ltd | Manufacturing | 2018 |
| Marshall Animal Health Consultancy Limited | Professional & scientific | 2023 |
| Marshalls Yard Limited | Real estate | 2003 |
| Marson Industrial Supplies Limited | Wholesale & retail | 1983 |
| Marston's Trailer Services Ltd | Wholesale & retail | 2020 |
| Marta Cohen Limited | Health & social care | 2009 |
| Martace Ltd | Wholesale & retail | 2021 |
| Martello Tower Healthcare (UK) Limited | Health & social care | 2020 |
| Martez & Darkely Limited | Wholesale & retail | 2009 |
| Martha Golf Ltd | Wholesale & retail | 2021 |
| Martia Food Ltd | Hospitality | 2023 |
| Martin Brookes Equine Dental Services Limited | Professional & scientific | 2012 |
| Martin Brooks (Roofing Specialists) Limited | Construction | 1984 |
| Martin Christopher Lawlor Ltd | Extraterritorial | 2024 |
| Martin Coates Garden Studio Ltd | Administrative & support | 2026 |
| Martin Daniels Limited | Construction | 2014 |
| Martin Emergency Plumber & Drainage 24H Ltd | Construction | 2025 |
| Martin Hague Limited | Professional & scientific | 2009 |
| Martin Hinchcliffe Limited | Real estate | 2016 |
| Martin Hobbs Consulting Ltd | Professional & scientific | 2022 |
| Martin Joseph Ltd | Other services | 2013 |
| Martin LEE Vehicle Solutions Ltd | Wholesale & retail | 2021 |
| Martin Properties (South Yorkshire) Limited | Real estate | 2018 |
| Martin Standley Consultancy Limited | Education | 2015 |
| Martin Williams Construction Ltd | Construction | 2022 |
| Martin Wood Associates Ltd | Professional & scientific | 2016 |
| Martina Care Services Ltd | Health & social care | 2015 |
| Martins Distributions & Haulage Limited | Transport & logistics | 2013 |
| Martins Good to Go Limited | Wholesale & retail | 2011 |
| Martinzngrill Ltd | Wholesale & retail | 2024 |
| Martistry Nails Limited | Other services | 2021 |
| Martlet Accounting Limited | Professional & scientific | 2024 |
| Martyn Gregory Wealth Management Ltd | Financial services | 2020 |
| Martyna Leczycka Ltd | Extraterritorial | 2012 |
| Marula Management Ltd | Other services | 2019 |
| Marvel Boss Ltd. | Information & communication | 2024 |
| Marvel ICA Ltd | Education | 2026 |
| Marvel Projects UK CIC | Construction | 2022 |
| Marvel Training Ltd | Education | 2023 |
| Marvin Miller Solutions Limited | Information & communication | 2017 |
| Marwat Enterprise Limited | Wholesale & retail | 2026 |
| Marx.K Limited | Hospitality | 2020 |
| Mary & Olive Limited | Professional & scientific | 2014 |
| Mary Diaz Aesthetics Ltd | Other services | 2021 |
| Mary Digital Studio Ltd | Wholesale & retail | 2026 |
| Mary Genevieve Consulting Limited | Professional & scientific | 2024 |
| Mary Property Enterprise Ltd | Real estate | 2026 |
| Mary Ruth Care Services Limited | Health & social care | 2014 |
| Mary Street Property Limited | Real estate | 2014 |
| Mary Street Studios Ltd | Arts & recreation | 2024 |
| Maryfield Properties Ltd | Households | 2016 |
| Maryotrans Logistics Limited | Transport & logistics | 2014 |
| MAS HOLD1 Ltd | Construction | 2025 |
| Masa Collaborative Dining Limited | Hospitality | 2021 |
| Masala Fish Ltd | Hospitality | 2024 |
| Masala Rush Ltd | Hospitality | 2026 |
| Mascon Care Partners Ltd | Real estate | 2023 |
| Mascot Automotive Limited | Wholesale & retail | 2014 |
| Mascot Group Holdings Limited | Financial services | 2018 |
| Mascot Management Limited | Professional & scientific | 2001 |
| Masenviron Ltd | Other services | 2009 |
| Mash Consulting Ltd | Administrative & support | 2013 |
| Mash Digital Limited | Administrative & support | 2017 |
| Mashmash Media and Productions Limited | Information & communication | 2013 |
| Masih Property Holdings Ltd | Real estate | 2024 |
| Masir Limited | Wholesale & retail | 2024 |
| Maskrey Holdings Limited | Financial services | 2025 |
| Masley Motors Ltd | Wholesale & retail | 2026 |
| Mason Metal Recycling Limited | Water & waste | 2014 |
| Mason Thomas Law Limited | Professional & scientific | 2018 |
| Masonfine Limited | | 1984 |
| Masons Munch Ltd | Hospitality | 2025 |
| Maspo Ltd | Wholesale & retail | 2006 |
| Mass Appeal Properties Ltd | Real estate | 2021 |
| Mass Software Limited | Information & communication | 2023 |
| Massage Back in Shape Ltd | Transport & logistics | 2020 |
| Massarella & Co Ltd | Hospitality | 2010 |
| Massarella Catering Limited | Professional & scientific | 1981 |
| Massarella Restaurants Limited | Hospitality | 1992 |
| Massarella Supplies Limited | Professional & scientific | 1977 |
| Massawa Ltd | Wholesale & retail | 2018 |
| Masteel (UK) Limited | Wholesale & retail | 2002 |
| Master Chefs Cook Ltd | Hospitality | 2022 |
| Master Cleaning Services Limited | Administrative & support | 1984 |
| Master Educate Ltd | Education | 2019 |