| Manstri Limited | Transport & logistics | 2025 |
| Mantisflow Ltd | Hospitality | 2020 |
| Maple Brickwork Ltd | Construction | 2015 |
| Maple Bros Ltd | Construction | 2024 |
| Maple Crescent (Smeeth) Co. Limited | Households | 2020 |
| Maple Property and Development Limited | Real estate | 2022 |
| Maplegate Homes Limited | Construction | 1999 |
| Mapman Ltd | Administrative & support | 2016 |
| Mapparel Ltd | Wholesale & retail | 2023 |
| Maracine Trans Limited | Transport & logistics | 2025 |
| Marasi Ltd | Wholesale & retail | 2024 |
| Marax Construction Ltd. | Construction | 2015 |
| Marble Nominee Limited | Extraterritorial | 2014 |
| Marc German Electrical Ltd | Construction | 2018 |
| Marc Newton Associates (London) Limited | Professional & scientific | 2014 |
| March Construction Limited | Real estate | 1989 |
| Marchmount Limited | Other services | 2014 |
| Marco Building Limited | Construction | 2013 |
| Marco Finance Limited | Financial services | 2018 |
| Marcus & MAE Advisers Limited | Financial services | 2014 |
| Marfin Developments Ltd | Construction | 2021 |
| Margs Properties Limited | Real estate | 2024 |
| Marguerite Honey Limited | Information & communication | 2026 |
| Marhabaa Food Ltd | Hospitality | 2021 |
| Marian Boswall Landscape Design Limited | Professional & scientific | 2018 |
| Marie Emmanuel CIC | Wholesale & retail | 2024 |
| MARIF786 Ltd | Wholesale & retail | 2025 |
| Marine Dream Ltd | Manufacturing | 2021 |
| Marine Point (Management Company) Limited | Real estate | 1992 |
| Mario Moses Ltd | Transport & logistics | 2026 |
| Mario&R Construct Ltd | Construction | 2023 |
| Mario's Taxi Ltd | Transport & logistics | 2025 |
| Marion Weatherhead Consulting Ltd | Professional & scientific | 2009 |
| Marischal Road Ltd | Real estate | 2020 |
| Mariusz & SON Ltd | Construction | 2023 |
| Mark England Plastering Limited | Construction | 2012 |
| Mark Frost Limited | Arts & recreation | 2011 |
| Mark Groombridge Oak Frame's & Restoration Limited | Administrative & support | 2015 |
| Mark H a Francis Limited | Information & communication | 2016 |
| Mark Hanton Studio Limited | Professional & scientific | 2011 |
| Mark Hopkins Plumbing and Heating Limited | Construction | 2002 |
| Mark JD Adamson Limited | Agriculture & fishing | 2009 |
| Mark Pearson Associates Limited | Other services | 2016 |
| Mark Scott Arenas Ltd | Construction | 2022 |
| Markely Agency Limited | Professional & scientific | 2024 |
| Market Cross Mews Limited | Professional & scientific | 1999 |
| Market Pioneer International Corporation (UK) Ltd | Transport & logistics | 2023 |
| Market Town Crossfit Limited | Construction | 2014 |
| Marketing Muse Ltd | Administrative & support | 2022 |
| Marketworks Gravesend Limited | Hospitality | 2026 |
| Markmill Limited | Real estate | 1985 |
| Marks Creative Limited | Arts & recreation | 1996 |
| Marks Limited | Extraterritorial | 1988 |
| Marlborough (Isleworth) Limited | Real estate | 1986 |
| Marlborough Consulting Services Limited | Professional & scientific | 2019 |
| Marlborough Isleworth Motors Limited | Real estate | 2003 |
| Marlborough Isleworth Properties Limited | Real estate | 2003 |
| Marlie POP Ltd | Information & communication | 2019 |
| Marmo Lusso Ltd | Wholesale & retail | 2023 |
| Maroanpoth Limited | Financial services | 2020 |
| Marr Estates Ltd | Real estate | 2020 |
| Marrakesh International Properties (Ascot) Limited | Real estate | 2005 |
| Marriage Tax Allowance Limited | Professional & scientific | 2016 |
| Marriott Recruitment Limited | Administrative & support | 2022 |
| Mars Celebration Limited | Real estate | 2023 |
| Mars Enterprise Ltd | Wholesale & retail | 2020 |
| Marsh Hospitality Group Ltd | Hospitality | 2024 |
| Marsh Mushroom Garden Services Limited | Households | 2020 |
| Marsh Tyre Services Ltd | Wholesale & retail | 2020 |
| Marshall Brickwork Ltd | Administrative & support | 2024 |
| Marshall Domains Ltd | Other services | 2012 |
| Marstanal Ltd | Other services | 2020 |
| Marta Creation Ltd | Professional & scientific | 2019 |
| Martello Marine Limited | Transport & logistics | 2019 |
| Martin Clifton Limited | Agriculture & fishing | 1959 |
| Martin Moate Bespoke Joinery Limited | Manufacturing | 2016 |
| Martin Roofing Services Limited | Construction | 2008 |
| Martin Shipp Ltd | Manufacturing | 2021 |
| Martin the Builder Ltd | Construction | 2020 |
| Martins Estates Property Management Ltd | Administrative & support | 2017 |
| Marton Recruitment Limited | Administrative & support | 2006 |
| Marush Artist Ltd | Other services | 2016 |
| Maruti Elevator Interiors UK Ltd | Professional & scientific | 2025 |
| Maruwa Europe Ltd. | Manufacturing | 1998 |
| Marvellous Project Services Limited | Professional & scientific | 2017 |
| Mary Davidson Associates Limited | Households | 2014 |
| Marzipan Investments Limited | Real estate | 2019 |
| MAS FM Ltd | Administrative & support | 2024 |
| Mash Commodity Ltd | Wholesale & retail | 2022 |
| Mashup TV Ltd | Information & communication | 2018 |
| Mason Carpentry Limited | Construction | 2002 |
| Mason Manor Homes Ltd | Real estate | 2023 |
| Mason's Logistics Services Ltd | Transport & logistics | 2023 |
| Masons Hair and Beauty Ltd. | Wholesale & retail | 2012 |
| Mast Express Limited | Transport & logistics | 2019 |
| Master Regalia Limited | Wholesale & retail | 2026 |
| Master Traders Club Ltd | Education | 2024 |
| Masterkey Property Holdings Ltd | Real estate | 2025 |
| Masters & Sons Limited | Professional & scientific | 2012 |
| Masterscreed Ltd | Wholesale & retail | 2016 |