| Magdalen 007 Ltd | Real estate | 2016 |
| Magic Boulevard Ltd | Wholesale & retail | 2025 |
| Magic Connections Limited | Information & communication | 2005 |
| Magic HAT Creative Ltd | Arts & recreation | 2025 |
| Magic Hour Holdings Limited | Financial services | 2021 |
| Magical Connection Limited | Arts & recreation | 2025 |
| Magnanimity Limited | Financial services | 2020 |
| Magnate Media Limited | Professional & scientific | 2015 |
| Mahdi Ltd | Real estate | 2015 |
| Maia Care Limited | Wholesale & retail | 2016 |
| Main Maintain Ltd | Administrative & support | 2017 |
| Main Titles Associates Limited | Professional & scientific | 1971 |
| Main Titles Limited | Financial services | 1964 |
| Mainshaw Limited | Professional & scientific | 2024 |
| Maintenance & Plumbing Ltd | Energy | 2016 |
| Maison Mayfair Ltd | Real estate | 2025 |
| Maison Rhed Limited | Arts & recreation | 2023 |
| MAJ Ltd | Arts & recreation | 2021 |
| Majestic Carriages Limited | Transport & logistics | 2024 |
| Majfibre Ltd | Construction | 2020 |
| MAK Aviation Limited | Education | 2015 |
| Make Moore & Groove Ltd. | Professional & scientific | 2011 |
| Making Khums Digital (MKD) Limited | Other services | 2022 |
| Mala Rentals Ltd | Real estate | 2022 |
| Malamco Trading Company Limited | Real estate | 1984 |
| Malbec Facilities LLP | | 2016 |
| Malfan Ltd | Manufacturing | 2020 |
| Malindi Court Management Limited | Real estate | 1999 |
| Malka Estates Limited | Real estate | 2022 |
| Mall OPS Ltd | Hospitality | 2019 |
| Mallott Media Limited | Administrative & support | 2011 |
| Malmo International Ltd | Wholesale & retail | 2024 |
| Malone Markets Ltd | Professional & scientific | 2019 |
| Malvin Group Ltd | Wholesale & retail | 2021 |
| Mama Cinger Ltd | Financial services | 2020 |
| Mamado International Limited | Wholesale & retail | 2007 |
| MAN N Van Ltd | Transport & logistics | 2023 |
| Mana and WAK Community Interest Company | Health & social care | 2026 |
| Manana Creative Limited | Information & communication | 2017 |
| Manchester Skips (UK) Ltd | Administrative & support | 1999 |
| Mango Technologies Ltd | Information & communication | 2012 |
| Manmi Medical Ltd | Health & social care | 2026 |
| Manna Records Ltd | Extraterritorial | 2024 |
| Manor Gardens (Stanmore) Management Company Limited | Households | 2002 |
| Manor Heights (Elstree) Management Limited | Households | 1995 |
| Manor Place (Management Company) Limited | Households | 2023 |
| Manor Way Management Company (NO. 1) Limited | Administrative & support | 2005 |
| Manorgate Baring Limited | Construction | 2020 |
| Manorgate Road Limited | Financial services | 2022 |
| Manorgroove Limited | Extraterritorial | 2026 |
| Manorside Electrical Ltd | Construction | 2010 |
| Mansouri Holdings Limited | Financial services | 2022 |
| Mantex Property Finance Unlimited | Financial services | 1946 |
| Manuella Care Property Limited | Real estate | 2023 |
| Manvi Enterprises Ltd | Administrative & support | 2023 |
| Manzanilla Eight Limited | Administrative & support | 2005 |
| Maple Court Drayton Road Management Company Limited(The) | Hospitality | 1986 |
| Maple Hill Capital Limited | Financial services | 2021 |
| Maple Leaf Property Investments Limited | Construction | 1993 |
| Maple Mews Management Company Limited | Real estate | 1986 |
| Maple Village Management Company Limited | Households | 1996 |
| Mapleleaf House Management Limited | Households | 1992 |
| Maps Brickwork Contractors Ltd | Construction | 2024 |
| Marabaloo | Information & communication | 2025 |
| Marble and Quartz Limited | Wholesale & retail | 2016 |
| March P E 15 Limited | Real estate | 2013 |
| Mardle Construction Ltd | Construction | 2022 |
| Margetts Property Development Limited | Real estate | 2026 |
| Margro CAP Ltd | Financial services | 2017 |
| Margro Developments Limited | Administrative & support | 2012 |
| Margro Properties Limited | Construction | 2010 |
| Mariam Abbas Ltd | Other services | 2023 |
| Marie Consultants Ltd | Professional & scientific | 2025 |
| Marilla Pictures Limited | Information & communication | 2018 |
| Marine Transmissions Ltd | Manufacturing | 2020 |
| Mariners Services Limited | Administrative & support | 2008 |
| Marini Italia Ltd | Construction | 2016 |
| Mariom Construction Ltd | Construction | 2016 |
| Mariusg Ltd | Financial services | 2024 |
| Mark D Props Ltd | Arts & recreation | 2022 |
| Mark Hutchinson Management Limited | Professional & scientific | 2012 |
| Markavon Limited | Professional & scientific | 2020 |
| Market Homes Ltd | Real estate | 2011 |
| Market Square Dental Practice Limited | Health & social care | 2015 |
| Marketing and Business Services Limited | Administrative & support | 2004 |
| Marlborough Finco Ltd | Real estate | 2022 |
| Marlborough Prop Co Ltd | Financial services | 2018 |
| Marlborough UK Hold Co Ltd | Financial services | 2018 |
| Marmalade Cash Limited | Real estate | 2022 |
| Marotiri Touring LLP | | 2018 |
| Marque House Limited | Financial services | 2023 |
| Mars Plus Ltd | Real estate | 2021 |
| Mars Secure Transport & Recruitment Service Ltd | Transport & logistics | 2015 |
| Marsbitz Innovations Ltd | Information & communication | 2025 |
| Marshfox Limited | Professional & scientific | 2018 |
| Marsk Group Limited | Administrative & support | 2020 |
| Marta Solutions Limited | Construction | 2019 |
| Martelle Limited | Health & social care | 1981 |
| Martin Morrell Studio Limited | Administrative & support | 2015 |
| Martin Rookes Props Ltd | Arts & recreation | 2018 |