| Maintenx Group Ltd | Construction | 2025 |
| Maison M Ltd | Wholesale & retail | 2017 |
| Majesa Limited | Wholesale & retail | 1989 |
| Maji Management Ltd | Other services | 2018 |
| Make Iterate Ltd | Professional & scientific | 2024 |
| Makeda Alleyne Programmes Ltd | Professional & scientific | 2019 |
| Makeitso Project Limited | Wholesale & retail | 2020 |
| Maker Entertainment Ltd | Wholesale & retail | 2026 |
| Malin & SON Property Ltd | Real estate | 2021 |
| Maltings Close Management Company Limited | Households | 1992 |
| Mama Rosa's Limited | Hospitality | 2003 |
| Man-Machine Interface Solutions Limited | Manufacturing | 1997 |
| Mandali Ltd | Other services | 2026 |
| Mandeville Place (Brampton) Management Company Limited | Households | 2018 |
| Mango Nails Ltd | Other services | 2024 |
| Manic Monday Limited | Information & communication | 1998 |
| Mann Brothers Media Limited | Information & communication | 1983 |
| Mann Motors (Leighton Buzzard) Limited | Wholesale & retail | 1986 |
| Manor Court Management (Old Linslade) Limited | Households | 1994 |
| Manorgrove Developments Limited | Real estate | 2002 |
| Manorgrove Holdings Ltd | Financial services | 2009 |
| Manorgrove Homes (UK) Ltd | Real estate | 2006 |
| Manorgrove Homes Construction Ltd | Construction | 2018 |
| Manorgrove Homes Ltd. | Construction | 1995 |
| Manorgrove Properties Limited | Construction | 2017 |
| Manser Estates Limited | Construction | 1986 |
| Mantari Advisory Ltd | Professional & scientific | 2026 |
| Mapama Limited | Information & communication | 2018 |
| Maple House (Hemel Hempstead) Management Limited | Households | 2022 |
| Maple Lawns (Amersham) Management Limited | Households | 2010 |
| Maple Mews (Leighton Buzzard) Management Company Limited | Extraterritorial | 2005 |
| Marc Fire Protection Ltd | Manufacturing | 2019 |
| Marconstruct Limited | Construction | 2013 |
| Marine Department Ltd | Arts & recreation | 2018 |
| Mark Amodio Services Ltd | Professional & scientific | 2026 |
| Mark Blower Ltd | Transport & logistics | 2019 |
| Mark Kitson Consulting Ltd | Professional & scientific | 2012 |
| Mark White & Associates Ltd | Professional & scientific | 2018 |
| Market Mews Management Company Limited | Real estate | 2001 |
| Marklove Ltd | Information & communication | 2026 |
| Marquez (LB) Limited | Manufacturing | 2016 |
| Marshalls Coaches LLP | | 2005 |
| Martian Supersonic Jets Ltd | Professional & scientific | 2022 |
| Martin Attachments UK Ltd. | Manufacturing | 2003 |
| Martyn Brown Ltd | Construction | 2019 |
| Martyn Weir Limited | Real estate | 2000 |
| Marvellous Plumbing and Heating Ltd | Construction | 2023 |
| Maryla Lodge Limited | Real estate | 2025 |
| Mascoz Ltd | Arts & recreation | 2019 |
| Matchhaus Limited | Information & communication | 2019 |
| Matecolm Limited | Real estate | 2023 |
| Matelier Limited | Professional & scientific | 2021 |
| Mateo's Food Truck Ltd | Hospitality | 2025 |
| Materia Consulting Limited | Professional & scientific | 2021 |
| Mateva Limited | Hospitality | 2023 |
| Matilda's Dog Grooming Ltd | Other services | 2023 |
| Matrix Asbestos Limited | Professional & scientific | 2025 |
| Matty Logistics Ltd | Transport & logistics | 2021 |
| Maven Tutors Limited | Education | 2023 |
| MAX Wellstead Limited | Real estate | 2020 |
| Maximum Supplements Ltd | Wholesale & retail | 2009 |
| Maydom in England Limited | Construction | 2019 |
| Maydom Limited | Extraterritorial | 2023 |
| Mayfair Partners Holdings Ltd. | Real estate | 2022 |
| Mayfield Water Solutions Ltd | Construction | 2023 |
| MBR Plant Hire Ltd | Administrative & support | 2025 |
| MC Accounting Services Limited | Professional & scientific | 2003 |
| MC Business Consulting Limited | Professional & scientific | 2008 |
| MC Change Solutions Ltd | Professional & scientific | 2023 |
| MC153 Limited | Professional & scientific | 2000 |
| MC2 Electrical Limited | Administrative & support | 2005 |
| Mcall Limited | Real estate | 2021 |
| Mccann Property Maintenance MK Ltd | Administrative & support | 2025 |
| Mcconnell Management Limited | Other services | 2019 |
| Mccontent & Design Limited | Information & communication | 2017 |
| MCD Products & Services Limited | Professional & scientific | 2015 |
| Mcgiff Developments Limited | Construction | 2014 |
| Mcgoldrick Construction Limited | Construction | 2024 |
| MCP Property Ltd | Real estate | 2026 |
| Mcpat Ltd | Health & social care | 2020 |
| MD Maisonettes Limited | Real estate | 2014 |
| MD SSC Ltd | Education | 2024 |
| Meadow Building & Investments Ltd | Construction | 2018 |
| Meaujo TUG Limited | Hospitality | 2004 |
| Mechanical Maintenance Solutions UK Ltd | Manufacturing | 2015 |
| Mechanicalade Ltd | Wholesale & retail | 2024 |
| Med-I-Pant (U.K.) Limited | Wholesale & retail | 1992 |
| Medicalert Trading Limited | Professional & scientific | 2013 |
| Medino Online Ltd | Wholesale & retail | 2017 |
| Medstack Ltd | Information & communication | 2025 |
| Meethere Limited | Other services | 2025 |
| Megha HR Ltd | Information & communication | 2022 |
| Melgab Media Ltd | Information & communication | 2019 |
| Meliora Holding Ltd | Professional & scientific | 2021 |
| Mellow App Limited | Wholesale & retail | 2023 |
| Menage Global Ltd | Hospitality | 2024 |
| Menka Limited | Real estate | 2017 |
| Mentmore Court Residents Association Limited | Real estate | 1988 |
| Mentmore Foods Limited | Wholesale & retail | 1994 |
| Mentmore Marina Ltd | Real estate | 2016 |