| Mama Cacao Ltd | Manufacturing | 2025 |
| Mama VEE Afro Market Ltd | Wholesale & retail | 2026 |
| Mamlouk Ltd | Hospitality | 2016 |
| Mamma Gina Limited | Hospitality | 2023 |
| MAN About a Plan Ltd | Professional & scientific | 2020 |
| Manafu Cladding Ltd | Construction | 2017 |
| Managed Technology Investors | | 1983 |
| Manageis Limited | Information & communication | 2013 |
| Manalive (UK) Limited | Arts & recreation | 2014 |
| Manalive Fitness Ltd | Arts & recreation | 2013 |
| Manav Dhillon Limited | Wholesale & retail | 2012 |
| Mandalia Trading Limited | Health & social care | 2025 |
| Mandap Magic Ltd | Administrative & support | 2026 |
| Mandate Investment Holdings Ltd | Real estate | 2022 |
| Mandaville Limited | Hospitality | 2022 |
| Mane Contract Services Limited | Administrative & support | 1993 |
| Manfar UK Ltd | Wholesale & retail | 2021 |
| Manfluence Ltd | Information & communication | 2025 |
| Mangal Pasha Ltd | Hospitality | 2024 |
| Manha and ANT Ltd | Hospitality | 2015 |
| Maniaa Tech Ltd | Information & communication | 2016 |
| Maniani Construction Limited | Construction | 2025 |
| Manmit Ltd | Education | 2024 |
| Mann Signalling Limited | Professional & scientific | 2014 |
| Manning & Boyce Bodywork Repair Ltd | Wholesale & retail | 2025 |
| Mannymation Ltd. | Information & communication | 2007 |
| Manor Asset Management Ltd | Real estate | 1998 |
| Manor Court (Radlett) Residents Association Limited | Real estate | 1994 |
| Manor Court Properties (UK) Limited | Administrative & support | 2003 |
| Manor Investments Limited | Construction | 2011 |
| Manor Parade Residents Management Limited | Households | 1997 |
| Mansion Residential Limited | Real estate | 2023 |
| Mansonthemove Limited | Transport & logistics | 2023 |
| Mansonthemove Properties Limited | Real estate | 2024 |
| Manss Ltd | Real estate | 2021 |
| Mansy's Care Limited | Administrative & support | 2025 |
| Manu MS Limited | Real estate | 2023 |
| Manufakture Ltd | Wholesale & retail | 2024 |
| Manuflex Consultancy Limited | Professional & scientific | 2026 |
| Manve Ltd | Real estate | 2024 |
| Manyan Ltd | Real estate | 2016 |
| MAP Haulage Watford Ltd | Agriculture & fishing | 2024 |
| MAP Site Services Ltd | Construction | 2025 |
| Mapac Group Limited | Wholesale & retail | 1961 |
| Mapac Limited | Professional & scientific | 1999 |
| Maple Hotels Management Company Limited | Hospitality | 1982 |
| Maple Sales Limited | Real estate | 2016 |
| Maplin Consultancy Services Limited | Professional & scientific | 2024 |
| Mapna Construction Ltd | Construction | 2020 |
| MAQ Builders Ltd | Construction | 2024 |
| Maqga Abbotswood Ltd | Health & social care | 2020 |
| Maral Property Management Limited | Households | 2019 |
| Marathon Motors Limited | Wholesale & retail | 2017 |
| Marban Ltd | Construction | 2021 |
| Marblerock Limited | Information & communication | 2016 |
| Marbuild UK Ltd | Construction | 2011 |
| Marc Becker Law Limited | Professional & scientific | 2017 |
| Marc BEE Joinery Ltd | Construction | 2025 |
| Marc Cohen Consulting Limited | Professional & scientific | 2018 |
| Marcia Lanyon Limited | Wholesale & retail | 1978 |
| Margalla Technologies Limited | Information & communication | 2007 |
| Maria Churros Limited | Hospitality | 2021 |
| Maricof Ltd | Hospitality | 2023 |
| Marie Assessments Limited | Public administration | 2024 |
| Marifat Capital Ltd | Professional & scientific | 2019 |
| Marigold Care Homes Ltd | Financial services | 2022 |
| Marigold MG1 Holdco Ltd | Health & social care | 2022 |
| Marigold MG1 Ltd | Health & social care | 1978 |
| Marigold MG2 Ltd | Health & social care | 2019 |
| Marimar Luxury Limited | Construction | 2026 |
| Marina One Freehold Company Limited | Households | 2001 |
| Marina One Management Limited | Households | 1996 |
| Marine Logistics Gold Mining Limited | Mining & quarrying | 2020 |
| Mariner Concepts Limited | Professional & scientific | 1998 |
| Mariner Developments Limited | Extraterritorial | 1996 |
| Marintech Safety Limited | Wholesale & retail | 2025 |
| Mario Cars Ltd | Wholesale & retail | 2024 |
| Marion Residential Relocations Limited | Financial services | 2018 |
| Marisafsec (Maritime Safety & Security Consultancies) Limited | Professional & scientific | 2017 |
| Maritteo Construction Ltd | Construction | 2024 |
| Marius Olteanu Ltd | Transport & logistics | 2023 |
| Mark & Manisha Limited | Information & communication | 2009 |
| Mark Beard Electrical Services Ltd | Construction | 2014 |
| Mark IT Consultants Ltd | Information & communication | 2025 |
| Mark P Cubitt Consultants Limited | Professional & scientific | 2014 |
| Mark Paytr Litchard Limited | Professional & scientific | 2007 |
| Mark Stern Property Ltd | Real estate | 2021 |
| Mark Ward Associates Ltd | Professional & scientific | 2021 |
| Mark-One Driving School Ltd | Education | 2024 |
| Market Place Residents Association Limited | Households | 2002 |
| Marketing Operations Hub Ltd | Professional & scientific | 2026 |
| Marketing Right Ltd | Real estate | 2020 |
| Marketplace Freehold Limited | Households | 2013 |
| Marketplace Human Resources Limited | Administrative & support | 1999 |
| Marketplace Online Ltd | Wholesale & retail | 2019 |
| Markits (UK) Ltd | Manufacturing | 2003 |
| Markka LLP | | 2010 |
| Marlborough Heights (Management Company) Limited | Households | 1979 |
| Marlena Beauty Academy Ltd | Other services | 2022 |
| Marleoo Ltd | Wholesale & retail | 2022 |