| Mango Networks Ltd | Information & communication | 2019 |
| Manisha Jethwa Ltd | Health & social care | 2009 |
| Mankan Limited | Financial services | 2026 |
| Mann Arts Ltd | Education | 2026 |
| Mann Chopra Enterprises Ltd | Other services | 2020 |
| Mannheim Ventures Ltd | Financial services | 2019 |
| Manor Care Ltd | Health & social care | 2021 |
| Manor House Drive Management Company Limited | Real estate | 2008 |
| Mansheen Enterprises Ltd | Wholesale & retail | 2012 |
| MANTRAS9 Ltd | Professional & scientific | 2025 |
| Mapletree Properties Limited | Real estate | 2022 |
| Marcford Limited | Health & social care | 1994 |
| Marco Polo Enterprises Limited | Wholesale & retail | 2002 |
| Marco Polo Properties Limited | Real estate | 2015 |
| Marjans Ltd | Hospitality | 2023 |
| Marjul Limited | Real estate | 2022 |
| Marjul Properties (Gateshead) Limited | Real estate | 2025 |
| Marjul Properties (Rugby) Limited | Real estate | 2025 |
| Mark Lewis Purapharma Ltd | Professional & scientific | 2020 |
| Mark Lewis Transport Limited | Transport & logistics | 2010 |
| Marlin Shipping Limited | Transport & logistics | 1988 |
| Marstone Homes Limited | Real estate | 2003 |
| Martal Consultants Limited | Real estate | 1993 |
| Martina Thomas Limited | Other services | 2017 |
| Mary Spillane Limited | Administrative & support | 2010 |
| MAS Media Global Limited | Information & communication | 2022 |
| Master Tech Commercials Ltd | Wholesale & retail | 2011 |
| Masterfesto Limited | Information & communication | 2017 |
| Mastermac Civils Limited | Construction | 2026 |
| Mastermac Haulage Limited | Transport & logistics | 2024 |
| Mastermac Holdings Limited | Financial services | 2022 |
| Mastermac Plant Hire Limited | Construction | 2022 |
| Mastermac Surfacing Limited | Construction | 2020 |
| Masv Assets Ltd | Financial services | 2026 |
| Mathematica Academy Ltd | Professional & scientific | 2010 |
| Matt Booth Studio Ltd | Arts & recreation | 2026 |
| Matt Engineering Ltd | Professional & scientific | 2024 |
| Mavender Ltd | Information & communication | 2023 |
| Maxilux Services Ltd | Professional & scientific | 2018 |
| MAY & Thomson Ltd | Wholesale & retail | 2002 |
| MAY Nails 70 Ltd | Other services | 2025 |
| Maya Mental Fitness Ltd | Other services | 2024 |
| Mayfair Impex (UK) Ltd | Wholesale & retail | 2020 |
| Mayfair Manor London Limited | Other services | 2023 |
| Maygrove Convenience Store Ltd | Wholesale & retail | 2021 |
| Mazda Limited | Health & social care | 2019 |
| MC Childcare Ltd | Health & social care | 2015 |
| MC Electricals London Ltd | Construction | 2023 |
| MC Renovations (London) Ltd | Construction | 2025 |
| Mcdermott Medical Limited | Health & social care | 2010 |
| Mchuzi Holdings Ltd | Real estate | 2019 |
| MCI Services (UK) Limited | Professional & scientific | 2011 |
| Mcq-Marketing Ltd | Professional & scientific | 2021 |
| Mcqueen's Group Holdings Limited | Wholesale & retail | 2015 |
| Mcqueen's Group LLP | | 2015 |
| MD Audio Consultants Limited | Professional & scientific | 2011 |
| MD Convenience Store Limited | Wholesale & retail | 2023 |
| MD Hot Food Ltd | Hospitality | 2026 |
| MDH Investments Limited | Manufacturing | 2001 |
| MDP Investments Ltd | Households | 2024 |
| MDT R-69 Holdings & Investments Limited | Administrative & support | 2022 |
| Meadowridge Properties Limited | Real estate | 2005 |
| Medical Object Oriented Software Enterprises Limited | Information & communication | 1998 |
| Medical Object Oriented Software Technology Limited | Information & communication | 1998 |
| Mehdi MED Ltd | Hospitality | 2016 |
| Mehina Ltd | Wholesale & retail | 2020 |
| Meili Wellbeing Sallon Ltd | Health & social care | 2025 |
| Melem'Is Ltd | Transport & logistics | 2018 |
| Meliort Ltd | Information & communication | 2023 |
| Melisi (Northwood) Limited | Hospitality | 2018 |
| Memberstate Limited | Real estate | 1993 |
| Menaria & Wilma Ltd | Administrative & support | 2019 |
| Mend-Rite Ltd | Construction | 2018 |
| Meraaki House Limited | Wholesale & retail | 2025 |
| Meraas London Ltd | Households | 2021 |
| Merali's Optical Services Limited | Health & social care | 2014 |
| Merchant Taylors' School Enterprises Limited | Education | 1988 |
| Mercury Events Limited | Hospitality | 2023 |
| Meshhh Limited | Financial services | 2021 |
| Message Consulting Limited | Professional & scientific | 2017 |
| Metcore Securities Ltd. | Professional & scientific | 2002 |
| Method Driving School Ltd | Education | 2025 |
| Metropolitan Properties (London) Limited | | 1984 |
| MEV Holdings Limited | Real estate | 2021 |
| Mexcrown Investments Limited | Real estate | 2007 |
| Mexlar Limited | Wholesale & retail | 2023 |
| Meyer Accountants Ltd | Professional & scientific | 2016 |
| MGC Analysis & System Design Limited | Information & communication | 1984 |
| Mica Building Services Limited | Construction | 2024 |
| Micasa Group Limited | Professional & scientific | 2004 |
| Micasa Limited | Real estate | 2004 |
| Micasa New Homes (Kings Langley) Limited | Real estate | 2007 |
| Micasa New Homes (Slough) Limited | Real estate | 2007 |
| Micasa New Homes Limited | Real estate | 2004 |
| Micasa Property Investments Limited | Real estate | 2005 |
| Micasa Property Services Limited | Wholesale & retail | 2003 |
| Michael Bradley Ltd | Information & communication | 2015 |
| Midas Property Associates Limited | Real estate | 2021 |
| Middlewich Properties Limited | Real estate | 2023 |
| Midlands Accommodation Limited | Hospitality | 2021 |