| M&A Deluxe Limited | Transport & logistics | 2018 |
| M&S Panayotovi Ltd | Transport & logistics | 2022 |
| M&V Brickwork Ltd | Construction | 2022 |
| M.J. Ryall Building Supplies Limited | Wholesale & retail | 1974 |
| M/S Oriontechspirits Private Limited | Information & communication | 2022 |
| MA Residential Ltd | Real estate | 2025 |
| MA Shreya Ltd | Health & social care | 2012 |
| MA SU Limited | Wholesale & retail | 2013 |
| Maadd Nurseries Limited | Administrative & support | 2021 |
| Machaon Limited | Health & social care | 2024 |
| Machine Music Publishing Limited | Information & communication | 2016 |
| Macys Security Ltd | Construction | 2014 |
| Maf-Bit Ltd | Transport & logistics | 2025 |
| Maggie Cleaning Ltd | Administrative & support | 2012 |
| Magic Arena Ltd | Hospitality | 2025 |
| Magic Masala Bricks Ltd | Hospitality | 2025 |
| Magnus Construction Group Ltd | Construction | 2022 |
| Magnus Facilities Management Ltd | Administrative & support | 2024 |
| Magnus Holdings Group Ltd | Financial services | 2024 |
| Magnus Property Group Ltd | Real estate | 2025 |
| Maha Green Gaia Limited | Information & communication | 2023 |
| Mailagent Limited | Information & communication | 2023 |
| Maison Henry Bertrand Limited | Wholesale & retail | 2023 |
| Maitynashe Care Ltd | Public administration | 2025 |
| Majestic Carpets (London) Limited | Administrative & support | 2014 |
| Majumder Pizza Ltd | Hospitality | 2022 |
| Malacusar Trans Ltd | Transport & logistics | 2022 |
| Mamu Bagna HF Ltd | Hospitality | 2022 |
| Mamu Fashions UK Limited | Manufacturing | 2015 |
| MAN I.T. (UK) Ltd | Information & communication | 2012 |
| Managed Moves Ltd | Transport & logistics | 2024 |
| Manchester Racquets and Healthtrack Limited | Professional & scientific | 1996 |
| Mandava and Chalasani Limited | Information & communication | 2016 |
| Manifxt Audio Limited | Wholesale & retail | 2025 |
| Manju Allcare Ltd | Wholesale & retail | 2025 |
| Manor Associates Limited | Financial services | 1981 |
| Mansells Heating Ltd | Construction | 2022 |
| Mansfield & Rhodes Developments Ltd | Real estate | 2014 |
| Mansfield & Rhodes Ltd | Real estate | 2013 |
| Mansory Sealants Limited | Manufacturing | 2025 |
| Manzel Limited | Real estate | 2024 |
| Maor Limited | Health & social care | 2025 |
| Mapalow Limited | Health & social care | 2015 |
| Mapperley Chapel Limited | Construction | 2006 |
| Maradzika Limited | Health & social care | 2019 |
| Maranatha Care Training Agency Limited | Health & social care | 2014 |
| Marble Arch Apartments RTM Company Ltd | Households | 2021 |
| Marble Property Investments Ltd | Real estate | 2014 |
| Marchmont Gate Management Limited | Households | 2003 |
| Marcin Hakiel Limited | Transport & logistics | 2016 |
| Maria Petkova Limited | Administrative & support | 2026 |
| Marigo Logistics Ltd | Wholesale & retail | 2017 |
| Marigo UK Ltd | Wholesale & retail | 2016 |
| Marina Point Developments Ltd | Construction | 2025 |
| Marine Action Ltd | Education | 2024 |
| Mario Pro Trans Ltd | Transport & logistics | 2026 |
| Mark Davies Logistics Limited | Transport & logistics | 2020 |
| Mark Williams PMP Limited | Professional & scientific | 2017 |
| Marketplace Simulation UK Limited | Education | 2006 |
| Markson Tennis and Leisure Centres Limited | Professional & scientific | 1990 |
| Marlborough Business Park Limited | Real estate | 2003 |
| Marlborough Oasis Limited | Construction | 2005 |
| Marlincroft Limited | Professional & scientific | 1978 |
| Marnic Ltd | Manufacturing | 2025 |
| MARONK9SECURITY Ltd | Administrative & support | 2025 |
| Maroon and Gold Limited | Construction | 2023 |
| Marque Marketing Ltd | Information & communication | 2026 |
| Mars Life Limited | Transport & logistics | 2025 |
| Marshall & Brown Limited | Wholesale & retail | 2018 |
| Marshall Wingfield Limited | | 1972 |
| Marshallways Ltd | Real estate | 2025 |
| Marter Investments Limited | Real estate | 1964 |
| Martin Buckeldee Associates Ltd | Professional & scientific | 2020 |
| Martin Construction General Building Ltd | Construction | 2017 |
| Martin Michaels Legal Services Ltd | Professional & scientific | 2024 |
| Marton Trans Ltd | Transport & logistics | 2016 |
| Marvikolaz Limited | Transport & logistics | 2026 |
| Masala HUT Hatfield Ltd | Hospitality | 2021 |
| Maskaj Ltd | Real estate | 2022 |
| Master Travel Coaches Limited | Extraterritorial | 2003 |
| Master Travel Passenger Services Limited | Transport & logistics | 2009 |
| Master YAW Limited | Other services | 2022 |
| Masterbill Measurement Services Limited | Professional & scientific | 2014 |
| Masterbill Measurement Systems Limited | Professional & scientific | 2002 |
| Masterbill Micro Systems Limited | Information & communication | 1981 |
| Mastermo Properties Limited | Real estate | 2025 |
| Masterpound Ltd | Wholesale & retail | 2019 |
| Mata Evolution Limited | Construction | 2022 |
| Matcha Magic UK Limited | Hospitality | 2025 |
| Matchmydog UK Ltd | Information & communication | 2025 |
| Matet Ltd | Hospitality | 2016 |
| Mather Estates Limited | Real estate | 2023 |
| Mather Marshall (Stevenage) Limited | Real estate | 2008 |
| Mather Marshall Limited | Real estate | 2003 |
| Maths Today Ltd | Education | 2020 |
| Matofield Limited | Real estate | 2023 |
| Matt Trans Ltd | Transport & logistics | 2023 |
| Mattjay Limited | Wholesale & retail | 2024 |
| Maven Innovative Technologies Ltd | Information & communication | 2010 |
| Maven Software Solutions Limited | Information & communication | 2006 |