| Macrocosm Consulting Limited | Information & communication | 2018 |
| MAD CUT Media Ltd | Administrative & support | 2026 |
| Madame Posh Limited | Other services | 2014 |
| Made by Annie Ltd | Arts & recreation | 2022 |
| Made Sacred Ltd | Wholesale & retail | 2026 |
| Madi Ltd | Administrative & support | 2024 |
| Madkangals Ltd | Construction | 2019 |
| Madras Biryani Junction Ltd | Hospitality | 2026 |
| MAE Consultancy & Services Ltd | Administrative & support | 2023 |
| Maeme's Watford Limited | Hospitality | 2019 |
| Magdalen Sutton Ltd | Education | 2018 |
| Magellanic Offshore Limited | Mining & quarrying | 2025 |
| Magic Finishes Ltd | Other services | 2014 |
| Magic Marketing (G.B.) Limited | Transport & logistics | 1990 |
| Magical Smiles Ltd | Health & social care | 2025 |
| Magjj's Ltd | Health & social care | 2023 |
| Magkan Solutions Limited | Information & communication | 2011 |
| Magna Building Services Ltd | Construction | 2016 |
| Magner Consulting Limited | Professional & scientific | 2018 |
| Magni Studios Ltd | Manufacturing | 2022 |
| Magnolia Drive Management Limited | Households | 2008 |
| Magnum Networks Limited | Information & communication | 2023 |
| Magnum Partner Estates Limited | Real estate | 2026 |
| Magpie Build Services Limited | Construction | 2015 |
| Mahika Property Investments Ltd | Real estate | 2025 |
| Maibelart Limited | Arts & recreation | 2019 |
| Maid Your Day Ltd | Administrative & support | 2017 |
| Maina Sparks Ltd | Construction | 2021 |
| Maintained Building Services Limited | Construction | 2018 |
| Maintainmyproperty Limited | Extraterritorial | 2023 |
| Maintenance Matters (London) Limited | Manufacturing | 2018 |
| Maitrics Services Ltd | Construction | 2021 |
| Majem Accountancy Limited | Professional & scientific | 2025 |
| Major Electrical Limited | Manufacturing | 1997 |
| Major League Gripping Ltd | Information & communication | 2019 |
| MAK 032 Limited | Construction | 2022 |
| MAK N ASH Ltd | Hospitality | 2018 |
| Make Collective Ltd | Administrative & support | 2016 |
| Making Rooms Construction Limited | Construction | 2020 |
| Making Rooms Limited | Construction | 2007 |
| MAKSI26 Ltd | Transport & logistics | 2026 |
| Maksimus Limited | Construction | 2017 |
| Maktech Properties Limited | Real estate | 2025 |
| Makwana Grocery Ltd | Wholesale & retail | 2025 |
| MAL Consulting Ltd | Real estate | 2015 |
| Malamova-Bravo Limited | Real estate | 2021 |
| Malayali Limited | Other services | 2025 |
| Male Grooming Ltd | Other services | 2019 |
| Malek Holdings Ltd | Real estate | 2017 |
| Mallow Management Limited | Professional & scientific | 2018 |
| Mama Umbrella Ltd | Arts & recreation | 2024 |
| Mamaar Ltd. | Information & communication | 2013 |
| Managed Operations AI Ltd | Administrative & support | 2000 |
| Management & Letting Services Ltd | Real estate | 2021 |
| Management Consultancy London Limited | Administrative & support | 2017 |
| Mandala Group Limited | Manufacturing | 2023 |
| Mandourco Limited | Professional & scientific | 2024 |
| Mango Chutney Limited | Information & communication | 2003 |
| Manna Care Homes Ltd | Health & social care | 2023 |
| Mannings Heath Golf Club Limited | Administrative & support | 2010 |
| Mano Systems Limited | Information & communication | 2011 |
| Manorpro Trading Ltd | Wholesale & retail | 2023 |
| Mantec Limited | Professional & scientific | 2016 |
| Mantle (Croydon) Ltd | Administrative & support | 2011 |
| Mantle (Sydenham) Limited | Other services | 2010 |
| Mantle Construction Ltd | Construction | 2009 |
| Mantle Developments UK Limited | Construction | 1992 |
| Mantle Eldon Court Ltd | Administrative & support | 2022 |
| Mantle Higher Drive Ltd | Administrative & support | 2022 |
| Mantle Investments Limited | Administrative & support | 1995 |
| Mantle Purley Limited | Professional & scientific | 2012 |
| Manugreen Team Ltd | Administrative & support | 2025 |
| Maple Accounting Services (UK) Ltd. | Professional & scientific | 2012 |
| Maple Court (Sutton) Freehold Limited | Real estate | 2013 |
| Maple Court (Sutton) Investors Limited | Real estate | 2014 |
| Maple Court (Sutton) Management Limited | Households | 1978 |
| Maple Forest Marketing Limited | Professional & scientific | 2009 |
| Maple Realty Limited | Real estate | 2024 |
| Maps Accounting Ltd | Professional & scientific | 2012 |
| Mapsan UK Ltd | Extraterritorial | 2020 |
| Marabella's Boutique Limited | Wholesale & retail | 2015 |
| Marang IT Limited | Administrative & support | 2005 |
| Marble Grange Group Limited | Administrative & support | 2024 |
| Marbles FD Limited | Administrative & support | 2012 |
| Marcela Llerena Consulting Ltd | Health & social care | 2025 |
| Marcela Llerena Investing Ltd | Financial services | 2019 |
| Marcus Lyall Limited | Arts & recreation | 2011 |
| Mardell Property Group Ltd | Real estate | 2018 |
| Marginelli Limited | Wholesale & retail | 2018 |
| Margining Technologies Limited | Information & communication | 2001 |
| Maria's Catering Ltd | Manufacturing | 2025 |
| MARIA2011 Limited | Transport & logistics | 2016 |
| Marianas Company Lettings Ltd | Real estate | 2013 |
| Marigona's Cakes and Bakes Ltd | Manufacturing | 2024 |
| Marina Residents Association Limited | Professional & scientific | 2001 |
| Marine Pro Limited | Professional & scientific | 1999 |
| Marius & David Limited | Construction | 2015 |
| Mark Anthony Capital Ltd | Real estate | 2021 |
| Mark Randall Consultancy Limited | Professional & scientific | 2016 |
| Market Analytics Technology Ltd | Information & communication | 2016 |