| Maebelle Ltd | Wholesale & retail | 2025 |
| Maeve Lorcan Limited | Professional & scientific | 2025 |
| Magevo Property Limited | Real estate | 2018 |
| Magevo UK Limited | Professional & scientific | 2014 |
| Magisters Lodge Management Co. Limited | Households | 1997 |
| Magnesium Health Ltd | Wholesale & retail | 2025 |
| Magnituud Limited | Information & communication | 2020 |
| Magnum Avenue Properties Ltd | Real estate | 2024 |
| Maidenhead Street Properties Limited | Real estate | 2013 |
| Main Road (Boreham) Management Company Limited | Households | 2016 |
| Maintake Limited | Information & communication | 2018 |
| Maison Furniture Limited | Administrative & support | 2012 |
| Maje Events Limited | Extraterritorial | 2020 |
| Malejo Ltd | Administrative & support | 2022 |
| Malo Consultants Ltd | Professional & scientific | 2020 |
| MAM International Limited | Wholesale & retail | 1978 |
| Mamo Zelo Ltd | Wholesale & retail | 2024 |
| Manaaki Healthcare Limited | Health & social care | 2019 |
| Management Company Services Limited | Real estate | 2004 |
| Management Secretaries Limited | Real estate | 2004 |
| Mandata Consultants Limited | Professional & scientific | 2002 |
| Mandeville Home Ltd | Professional & scientific | 2025 |
| Mandla Heating Solutions Limited | Construction | 2023 |
| Manduessedum Ltd | Extraterritorial | 2021 |
| Mangrove Park Residents Limited | Households | 2005 |
| Manifest Brand Development Ltd | Manufacturing | 2021 |
| Manor Lane Feltham Management Company Limited | Real estate | 2022 |
| Manor Law Ltd | Professional & scientific | 2012 |
| Manor Solutions Ltd | Professional & scientific | 2020 |
| Mansdale Management LLP | | 2024 |
| Mansfield Court Management Limited | Households | 1985 |
| Mansfield Freeholders Limited | Households | 2010 |
| Mansio Lettings Ltd | Real estate | 2022 |
| Manta Supply Chain Consulting Ltd | Professional & scientific | 2023 |
| Maplantic Ltd | Professional & scientific | 2019 |
| Marchase Limited | Financial services | 2005 |
| Mardea Construction Limited | Construction | 2008 |
| Marden Homes Limited | Construction | 1992 |
| Margaux Bleue Limited | Administrative & support | 2019 |
| Margetts Investments (Leaseholds) Ltd | Real estate | 2020 |
| Margetts Investments Leases Ltd | Real estate | 2019 |
| Margetts Investments Ltd | Real estate | 2019 |
| Maria Artaza Counselling & Guidance Practice Ltd | Professional & scientific | 2025 |
| Maria Dentistry Limited | Health & social care | 2018 |
| Maridom Properties Ltd | Real estate | 2025 |
| Mariners Walk Common Freehold (Herts) Limited | Households | 1996 |
| Mariners Walk Management (Herts) Limited | Households | 1990 |
| Mark Adrian Goodrich Ltd | Extraterritorial | 2025 |
| Mark Bailey Associates Limited | Administrative & support | 2000 |
| Mark Cussens Recruitment Limited | Administrative & support | 2025 |
| Mark Newton Associates Limited | Professional & scientific | 2014 |
| Mark Webster Dart Promotions Ltd | Arts & recreation | 2009 |
| Market Court (Hertford) Management Company Limited | Real estate | 2013 |
| Marking Tree Limited | Arts & recreation | 2010 |
| Marking Tree Technologies Limited | Information & communication | 2023 |
| Marlins House Limited | Information & communication | 2019 |
| Marsh Close Residents Company (Phase II) Limited | Households | 1978 |
| Marshall Accident Repair Centre Limited | Wholesale & retail | 2023 |
| Marshland House Ltd | Households | 2020 |
| Martelo and MO Ltd | Manufacturing | 2021 |
| Martin Glazebrook Mechanical Services Ltd | Manufacturing | 2014 |
| Martin Mathew & Co. Limited | Wholesale & retail | 1973 |
| Martin Ring Public Relations Limited | Professional & scientific | 2012 |
| Maryam Sofia Management Ltd | Hospitality | 2024 |
| Marymakingmoves Ltd | Arts & recreation | 2023 |
| Masra Solutions Ltd | Professional & scientific | 2024 |
| Master Chef Food Limited | Manufacturing | 2025 |
| Masterlite Limited | Other services | 2002 |
| Mate Productions Limited | Information & communication | 2024 |
| Materials Movement Investments Limited | Real estate | 2000 |
| Matey Productions Limited | Information & communication | 2005 |
| Matike Limited | Real estate | 2022 |
| Matt Hart Gardens and Landscaping Limited | Administrative & support | 2020 |
| Matt Sears & Sons Roofing Contractors Limited | Construction | 2010 |
| Mavericks Ventures Ltd | Financial services | 2023 |
| Maximitise Limited | Information & communication | 2023 |
| Maxtip Limited | Administrative & support | 2020 |
| May's Transport Limited | Transport & logistics | 2018 |
| Mayfields Consultancy Ltd | Professional & scientific | 2016 |
| Mayne Choice Plumbing Ltd | Construction | 2023 |
| Mazmoit Ltd | Information & communication | 2019 |
| MBI Contractors Ltd | Construction | 2017 |
| MBI Group Ltd | Real estate | 2019 |
| MBI Industrial Services Ltd | Construction | 2024 |
| MBI Medical Limited | Administrative & support | 2015 |
| MBI Medical Locums Ltd | Administrative & support | 2021 |
| MBI Solutions Ltd | Administrative & support | 2025 |
| MBI Staffing Ltd | Administrative & support | 2017 |
| Mbjsc (Properties) Limited | Real estate | 2002 |
| MBS Club Ltd | Hospitality | 2024 |
| Mcconnell Group Holdings Limited | Financial services | 2024 |
| Mcconnell Group Limited | Financial services | 2018 |
| Mcnulty Artist Management Ltd | Arts & recreation | 2022 |
| MCR Studio Limited | Professional & scientific | 2004 |
| Mdlobo Medical Services Limited | Health & social care | 2004 |
| MDT Fixing Ltd | Construction | 2011 |
| Mead Business Centre Management Limited | Real estate | 1988 |
| Mead Lane Management Limited | Professional & scientific | 1991 |
| Meader Risk Solutions Limited | Administrative & support | 2022 |
| Meadfield Court Management Company Limited | Households | 1992 |