| Maillet Consultancy Ltd. | Professional & scientific | 2014 |
| Maison Lewis Ltd | Information & communication | 2023 |
| Maison Mouse Ltd | Wholesale & retail | 2025 |
| Major, Lindsey & Africa - UK, Ltd | Administrative & support | 2003 |
| Major, Lindsey & Africa Services - UK, Ltd | Administrative & support | 2020 |
| Makasang Ltd | Real estate | 2025 |
| Make a Difference Initiative (Madi) CIC | Education | 2022 |
| Makini Recruitment Services UK Ltd | Health & social care | 2023 |
| Malzatech Limited | Professional & scientific | 2023 |
| Mammoth Business Group Ltd. | Wholesale & retail | 2017 |
| MANANDVAN247 Ltd | Transport & logistics | 2025 |
| Manchiu Limited | Hospitality | 2013 |
| Manhattan Skyline Limited | Professional & scientific | 1999 |
| Manik Fashion Limited | Wholesale & retail | 2025 |
| Manisain Ltd | Professional & scientific | 2025 |
| Mannat Foods Binfield Ltd | Wholesale & retail | 2026 |
| Mannava Associates Limited | Professional & scientific | 2010 |
| Mannava Enterprises Limited | Professional & scientific | 2023 |
| Manor Street Flats (Maintenance) Limited | Real estate | 1985 |
| Manuel Ventures Ltd | Wholesale & retail | 2026 |
| Manzeera Resources Limited | Real estate | 2021 |
| Marant Property Limited | Real estate | 2025 |
| Maravanyika Limited | Health & social care | 2011 |
| Marbud Limited | Construction | 2015 |
| Marina Balla Photography Ltd | Professional & scientific | 2020 |
| Mark Associates Limited | Hospitality | 2004 |
| Marka Dog Training Limited | Extraterritorial | 2021 |
| Marketing NUT Ltd | Professional & scientific | 2020 |
| Marketpoint (Europe) Limited | Information & communication | 1993 |
| Marketpoint (London) Limited | Professional & scientific | 1982 |
| Markrebeca Ltd | Transport & logistics | 2021 |
| Markyou Sports Cards Ltd | Wholesale & retail | 2025 |
| Marley's Flavours Ltd | Wholesale & retail | 2022 |
| Marleycroft Business Services Limited | Professional & scientific | 2003 |
| Martcaniks Limited | Wholesale & retail | 2017 |
| Martin & Fahy Accountants LLP | | 2001 |
| Martin Editorial Limited | Information & communication | 2010 |
| Martins Heron Car Valeting Ltd | Wholesale & retail | 2018 |
| Marton Meadows Management Company Limited | Households | 2021 |
| Martucci Real Estate Limited | Real estate | 2021 |
| Marval Software Limited | Information & communication | 1989 |
| Mask It-Infra Solutions Ltd | Information & communication | 2019 |
| Maskqueen Ltd | Wholesale & retail | 2009 |
| Mason Construction Management Ltd | Construction | 2024 |
| Mason David Limited | Construction | 2024 |
| Mason's Heating & Plumbing Ltd | Construction | 2016 |
| Mason's Properties Ltd | Real estate | 2026 |
| Massages & Wellness Ltd | Other services | 2025 |
| Masterheat Ltd | Construction | 2024 |
| MATER1974 Ltd | Hospitality | 2019 |
| Mathsole Limited | Professional & scientific | 2007 |
| Matse Enterprise Ltd | Professional & scientific | 2021 |
| Matt Browning Limited | Construction | 2009 |
| Matt Sutton Creative Ltd | Arts & recreation | 2021 |
| Matthew Jake Limited | Arts & recreation | 2008 |
| Mattomgeo Limited | Wholesale & retail | 2023 |
| Mattutes Ltd | Information & communication | 2009 |
| Maund Carpentry & Joinery Ltd | Construction | 2025 |
| Maverick Otter Limited | Professional & scientific | 2024 |
| Maxathon Limited | Professional & scientific | 2002 |
| Mayang Limited | Health & social care | 2025 |
| Mayfair Global Commodities Limited | Wholesale & retail | 2023 |
| Mayfield Live in Care Ltd | Health & social care | 2019 |
| Maynard Carpentry Limited | Construction | 2025 |
| Mayuresh Management Limited | Other services | 2005 |
| MAZ Utilities Ltd | Construction | 2021 |
| MB Group Limited | Financial services | 1988 |
| Mbasc Ltd | Professional & scientific | 2016 |
| MC Building Designer Ltd | Construction | 2018 |
| MC Leod Associates Limited | Information & communication | 2009 |
| MC Original Limited | Wholesale & retail | 2022 |
| MC3 LAB Ltd | Information & communication | 2020 |
| MCB Golf Ltd | Arts & recreation | 2025 |
| Mccormac Consulting Limited | Professional & scientific | 2019 |
| Mcgarry Interiors Ltd | Manufacturing | 2020 |
| Mcglinn Machinery Limited | Wholesale & retail | 2026 |
| Mckendrick Services Limited | Construction | 2015 |
| Mclaughlinagency Limited | Wholesale & retail | 2025 |
| Mcwonar Consulting Ltd | Information & communication | 2020 |
| MD Premier Services Limited | Construction | 2009 |
| MD Special Projects Limited | Construction | 2018 |
| MD Taxation Ltd | Professional & scientific | 2024 |
| MDE Health Technologies Ltd | Information & communication | 2022 |
| MDE Healthcare Services Limited | Information & communication | 2005 |
| MDE Horreum Ltd | Professional & scientific | 2021 |
| MDE Services Group Limited | Information & communication | 2016 |
| MDE Travel Limited | Administrative & support | 2016 |
| MDP IT Consulting Limited | Information & communication | 2017 |
| Mdss Ltd | Wholesale & retail | 2012 |
| MEA Designs Ltd | Wholesale & retail | 2023 |
| Meat & Greet Master Butchers Ltd | Wholesale & retail | 2025 |
| Meatloaf Homes Ltd | Real estate | 2020 |
| Mechanical Inspection Services Ltd | Professional & scientific | 2023 |
| Mechanical Ltd | Construction | 2024 |
| Medequine Ltd | Agriculture & fishing | 2025 |
| Medical Auctions (BMA) Limited | Wholesale & retail | 2015 |
| Medical Supplies Direct Ltd | Health & social care | 2018 |
| Medical Therapies Maidenhead Ltd | Health & social care | 2015 |
| Medici Development S Limited | Construction | 2025 |
| MEG a Lock Ltd | Administrative & support | 2010 |