| Market Genius Ltd | Professional & scientific | 2014 |
| Marketing Arrow Limited | Professional & scientific | 2010 |
| Marketing Strategico Ltd | Financial services | 2022 |
| Marketplace Bdms Limited | Administrative & support | 2007 |
| Markets Trading Ltd | Other services | 2015 |
| Markfair Limited | Real estate | 2005 |
| Marknewen Investments Limited | Real estate | 1962 |
| Marlborough Mountbatten Limited | Real estate | 2021 |
| Marle Place Property Limited | Real estate | 2009 |
| Marley House RTM Company Limited | Households | 2024 |
| Marni Consulting Ltd | Professional & scientific | 2010 |
| Marrey Tableware Limited | Wholesale & retail | 1994 |
| Martindale (Mortgages & Protection) Limited | Professional & scientific | 2014 |
| Martini Road Limited | Real estate | 2014 |
| Marushah Properties Limited | Real estate | 2013 |
| Maruti Brothers Group Limited | Construction | 2023 |
| Maruti Courier Services Limited | Transport & logistics | 2026 |
| Marutinandan Group Limited | Construction | 2023 |
| Marvasti Neurology 360 Ltd | Health & social care | 2025 |
| Marvellous Marvin Ltd | Wholesale & retail | 2015 |
| Marveltrade Ltd | Financial services | 2020 |
| Marvin the Stage Play Ltd | Arts & recreation | 2010 |
| Marwin Securities Limited | Construction | 1955 |
| Masala MK Limited | Hospitality | 2018 |
| Masalla Limited | Hospitality | 2019 |
| Masayang Buhay Limited | Health & social care | 2015 |
| Masefield Ventures Ltd | Real estate | 2017 |
| Mash UP London Limited | Other services | 2016 |
| Masham Group Ltd | Hospitality | 2025 |
| Maskhan Ltd | Other services | 2026 |
| Master Heating & Electrical Ltd | Professional & scientific | 2022 |
| Masters Art Limited | Wholesale & retail | 2022 |
| Matan Online Limited | Professional & scientific | 2008 |
| Mathematica Ltd | Information & communication | 2022 |
| Matisse Interior Limited | Construction | 2021 |
| Matrix Estates (UK) Limited | Real estate | 1998 |
| Matthew Logistic Limited | Transport & logistics | 2018 |
| Matthew Newman Ministries | Education | 2011 |
| Matthews Consortium Ltd | Real estate | 2024 |
| Matthews Enterprises Ltd | Real estate | 2021 |
| Matthews Music Management Ltd | Information & communication | 2007 |
| Maty Transport Ltd | Transport & logistics | 2017 |
| Mauray Enterprises Limited | Professional & scientific | 1982 |
| Maven Advisory Ltd | Professional & scientific | 2014 |
| Maven Corporate Ltd | Professional & scientific | 2009 |
| Maven Properties Limited | Real estate | 2019 |
| Mavi London Limited | Wholesale & retail | 2016 |
| Maxchlo Limited | Construction | 2023 |
| Maxim Label and Packaging (UK) Limited | Manufacturing | 2013 |
| Maxima Property Services Ltd | Construction | 2016 |
| Maxima Property Solutions Ltd | Construction | 2025 |
| Maximise Enterprises Limited | Arts & recreation | 1997 |
| Maximus AV Ltd | Arts & recreation | 2023 |
| Maxine Godley Ltd | Education | 2021 |
| Maxlift & Heavy Machines Ltd | Wholesale & retail | 2024 |
| Maxmechanical Services Ltd | Construction | 2018 |
| Maxwealth Consultancy Ltd | Information & communication | 2022 |
| Maxwealth Management Ltd | Real estate | 2024 |
| Maya Investments Limited | Financial services | 2005 |
| Maya Systems Limited | Information & communication | 2025 |
| Mayah Engineer Ltd | Construction | 2008 |
| Mayani Industrial Ltd | Real estate | 2020 |
| Mayara Speed Limited | Transport & logistics | 2025 |
| Mayday Motors (Roehampton) Limited | Wholesale & retail | 2010 |
| Maydiang (UK) Limited | Wholesale & retail | 2003 |
| Mayesbrook Autos Limited | Wholesale & retail | 2025 |
| Mayfair Capital Advisers Limited | Financial services | 2026 |
| Mayfair Chauffeurs Ltd | Transport & logistics | 2025 |
| Mayfair Green Holding Limited | Real estate | 2022 |
| Mayfair Luxe Collection Limited | Real estate | 2024 |
| Mayfair One Limited | Professional & scientific | 2012 |
| Mayivy Ltd | Health & social care | 2024 |
| Mayje Ltd | Professional & scientific | 2021 |
| Maylyn Limited | Wholesale & retail | 2023 |
| Mañana Productions Ltd | Arts & recreation | 2026 |
| MB Defence Services Limited | Professional & scientific | 2002 |
| MB Succession Planning Limited | Financial services | 2021 |
| MB19 Ltd | Hospitality | 2019 |
| MBL Carpentry Ltd | Construction | 2024 |
| MBS Wilts Limited | Hospitality | 2018 |
| Mbt-Il Properties Ltd | Real estate | 2021 |
| Mbtzur Properties Ltd | Real estate | 2022 |
| MC Build Services Limited | Construction | 2011 |
| MC Corutiu Electrical Ltd | Energy | 2016 |
| MCC Surveyors Limited | Professional & scientific | 2013 |
| Mchgs Limited | Hospitality | 2026 |
| MCM Film (Services) Limited | Construction | 2011 |
| MCM Site (Services) Limited | Construction | 2011 |
| Mcmahon Properties South East Limited | Construction | 2014 |
| Mcnature-Sc Limited | Wholesale & retail | 2022 |
| MD Consulting London Ltd | Professional & scientific | 2024 |
| Mdal Surfacing Ltd | Construction | 2021 |
| Mdea Consulting Ltd | Information & communication | 2017 |
| Mdrsh Properties Ltd | Real estate | 2021 |
| Meadowside Fetcham Limited | Professional & scientific | 2014 |
| Meadrose Ltd | Real estate | 2016 |
| Measured Space Limited | Professional & scientific | 2019 |
| Medarc Health Sciences Ltd | Information & communication | 2023 |
| Medaskai Ltd | Information & communication | 2025 |
| Media Studio Solution Ltd | Wholesale & retail | 2022 |