| Marlos Sandwich Bar Ltd | Hospitality | 2025 |
| Marlow Court Freehold Company Limited | Real estate | 1999 |
| Marlow Court Management Company Limited | Real estate | 1970 |
| Marray Ltd | Wholesale & retail | 2023 |
| Marrsbytes Limited | Information & communication | 2013 |
| Mars Online Ltd | Wholesale & retail | 2021 |
| Mars UK Properties Limited | Real estate | 2022 |
| Mars Vanguard Cars Ltd | Wholesale & retail | 2025 |
| Marsa Advisory Limited | Professional & scientific | 2019 |
| Marsden Taylor Consulting Ltd | Professional & scientific | 2024 |
| Marsh Hall Limited | Other services | 1990 |
| Marshall Close Management Company Limited | Real estate | 1983 |
| Marshall Mcgeever Limited | Professional & scientific | 2013 |
| Marshall N Jones Limited | Construction | 2012 |
| Marshall&Nair Limited | Information & communication | 2024 |
| Marshalls Close Freeholders Limited | Real estate | 2004 |
| Marshbridge Limited | Construction | 2015 |
| Marston Model Limited | Information & communication | 2025 |
| Marsubit Services Limited | Wholesale & retail | 2015 |
| Mart Point Ltd | Wholesale & retail | 2025 |
| Martenbrook Limited | Construction | 1973 |
| Martial Arts Locker Room Limited | Wholesale & retail | 2016 |
| Martin and Morgan UK Limited | Professional & scientific | 2018 |
| Martin Cook Electrical Services Limited | Manufacturing | 1998 |
| Martin Gustyn and Associates Ltd | Professional & scientific | 2012 |
| Martin Kelly Media Limited | Information & communication | 2015 |
| Martin Roberts at the Flower Shop Limited | Wholesale & retail | 2012 |
| Martindale Electric Company Limited | Manufacturing | 1997 |
| Martlet Research Ltd | Other services | 2005 |
| Marvin Sordell Limited | Other services | 2013 |
| Marward Services Limited | Information & communication | 2000 |
| Marylebone Maintenance Limited | Administrative & support | 2012 |
| Marymar Services Limited | Transport & logistics | 2015 |
| MAS Group, Limited | Professional & scientific | 2016 |
| Masara Consultancy Ltd | Information & communication | 2025 |
| Masat Properties Limited | Extraterritorial | 2021 |
| Mascot OUT of School Care Limited | Health & social care | 2006 |
| Mash Design Works Ltd | Professional & scientific | 2019 |
| Mashco Limited | Wholesale & retail | 1997 |
| Mass Complete Property Solutions Ltd | Construction | 2023 |
| Mass Properties Ltd | Real estate | 1997 |
| Mass Waste and Cleaning Services Ltd | Water & waste | 2023 |
| Massary Exchange Ltd | Wholesale & retail | 2019 |
| Massive Monster Limited | Information & communication | 2014 |
| Massive Traders Ltd | Wholesale & retail | 2006 |
| Mast Pond Wharf Limited | Construction | 2010 |
| Mastan Enterprises Limited | Wholesale & retail | 2021 |
| Master Builders Ltd | Construction | 2019 |
| Master Class Cambridge Limited | Administrative & support | 2011 |
| Master Construct Limited | Construction | 2025 |
| Master Crepes Limited | Hospitality | 2024 |
| Master Engineering Services Ltd | Professional & scientific | 2025 |
| Master Gourmet Meats Ltd | Manufacturing | 2010 |
| Masterfix Heating & Building Ltd | Construction | 2025 |
| Masterlord Holdings Limited | Financial services | 2026 |
| Mastermind Digital Ltd | Information & communication | 2022 |
| Mastermind Network Service Ltd | Wholesale & retail | 2012 |
| Masters of Roofing and Guttering Ltd. | Construction | 2020 |
| Masterslav Flooring Ltd | Construction | 2025 |
| Mastersplicing Ltd | Information & communication | 2022 |
| Mastertronic Vehicle Solutions Ltd | Wholesale & retail | 2021 |
| Mastic Pointing Services Limited | Construction | 1980 |
| MAT Capital Ltd | Financial services | 2026 |
| MAT Engineering Ltd | Construction | 2012 |
| MAT Logistik Ltd | Transport & logistics | 2025 |
| MAT UK Group Ltd | Other services | 2023 |
| Match Day Merchandise Limited | Administrative & support | 2016 |
| Mateas Group Ltd | Real estate | 2022 |
| Mateas Investments Ltd | Real estate | 2024 |
| Material Labs Ltd | Information & communication | 2017 |
| Matflow Limited | Professional & scientific | 2016 |
| Mathani Ltd | Information & communication | 2025 |
| Mati's Cake Limited | Hospitality | 2017 |
| Matka House Limited | Hospitality | 2025 |
| Matrix Roboticx Ltd | Manufacturing | 2024 |
| Matsana Group Limited | Professional & scientific | 2017 |
| Matt Green Consulting Ltd | Professional & scientific | 2024 |
| Matt Mcparland Limited | Professional & scientific | 2024 |
| Matthew 633 Ltd | Construction | 2018 |
| Matthew Arnold & Baldwin LLP | | 2009 |
| Matthew Cunningham Consultancy Limited | Professional & scientific | 2011 |
| Matthew Tumbridge Financial Advice Ltd | Professional & scientific | 2024 |
| Matthews Simply Connecting Ltd | Administrative & support | 1999 |
| Maurice & Sons Ltd | Real estate | 2013 |
| Mauritius Global Diaspora Limited | Other services | 2023 |
| Maurizio Restaurant Limited | Hospitality | 2011 |
| Mavaro Group Ltd | Wholesale & retail | 2025 |
| Maverick Costs Limited | Information & communication | 2024 |
| Mawson Gardens Residents Management Company Limited | Households | 2014 |
| MAX Apps Limited | Information & communication | 2011 |
| MAX Fire Solution Ltd | Construction | 2025 |
| MAX MAX Advisory Ltd | Professional & scientific | 2026 |
| MAX Signs Ltd | Professional & scientific | 2010 |
| Maxa Group Limited | Financial services | 2023 |
| Maxa Trading UK Ltd | Manufacturing | 2011 |
| Maxella Modes Limited | Real estate | 1950 |
| Maxfax Surgery Limited | Health & social care | 2016 |
| Maxi Ecommerce Limited | Transport & logistics | 2023 |
| Maxi House Ltd | Construction | 2021 |
| Maxie-Jaye Limited | Administrative & support | 1996 |