| Maldon Plumbers Limited | Construction | 2023 |
| Maldon Property U.K. Ltd | Real estate | 2021 |
| Maldon Saints YFC Limebrook Ltd | Other services | 2023 |
| Malgraves Ltd | Financial services | 2023 |
| Maliasha Estates LLP | | 2024 |
| Malins Roofing Ltd | Construction | 2001 |
| Maliora Limited | Administrative & support | 2026 |
| Mallus Kerala Enterprises Limited | Wholesale & retail | 2024 |
| Malret Ltd | Real estate | 2021 |
| Malvina (Eltham) Limited | Administrative & support | 1953 |
| Mama J & Co. Ltd | Health & social care | 2025 |
| Mambokadzi Limited | Health & social care | 2023 |
| Mampalam Property Limited | Real estate | 2025 |
| MAN Direct Services Group Ltd | Professional & scientific | 2017 |
| Manage and Build Group Limited | Construction | 2025 |
| Manage-Risk Surveys Limited | Administrative & support | 2002 |
| Managed Group Ltd | Information & communication | 2019 |
| Mandannic RTM Company Limited | Households | 2023 |
| Manford Media Ltd | Professional & scientific | 2018 |
| Manna Health Care Ltd | Health & social care | 2024 |
| Manning International Limited | Arts & recreation | 2021 |
| Manning Property Solutions Limited | Households | 2025 |
| Mannion Group Ltd | Administrative & support | 2019 |
| Manodale Properties Limited | Construction | 1978 |
| Manoloutsou Limited | Health & social care | 2012 |
| Manor Electrical Contractors Limited | Construction | 2003 |
| Mansergh Limited | Administrative & support | 2026 |
| Mansourpour Commercial Limited | Real estate | 2016 |
| Mansourpour Investment Ltd | Real estate | 2022 |
| Manthra Properties Limited | Real estate | 2025 |
| Mantraa Limited | Health & social care | 2022 |
| Manu Mathew ANP Services Ltd | Health & social care | 2025 |
| Manuel Sechi Limited | Information & communication | 2018 |
| MAP Plant Limited | Administrative & support | 1999 |
| Maple Property EN Ltd | Real estate | 2026 |
| Maplewood Grove (Dunmow) Management Company Limited | Households | 2026 |
| Mapp Properties Limited | Real estate | 2002 |
| Mapp Property Investments Limited | Real estate | 2023 |
| Maps Financial Services Limited | Financial services | 2014 |
| Marbar London Ltd | Construction | 2019 |
| Marble County Limited | Real estate | 2014 |
| Marcanda Investments Limited | Financial services | 2014 |
| Marcoms Consulting Ltd | Professional & scientific | 2020 |
| Marconi Sailing Club Ltd | Arts & recreation | 2003 |
| Mardon Music Limited | Professional & scientific | 2017 |
| Mares Group Limited | Professional & scientific | 2002 |
| Mariam Logistics Ltd | Transport & logistics | 2025 |
| Marigeo Ltd | Transport & logistics | 2015 |
| Marigold Butterfly Limited | Information & communication | 2022 |
| Marina Bar and Restaurant Limited | Hospitality | 2014 |
| Marina One Security Services Ltd | Information & communication | 2006 |
| Marine and General Industrial International Company Limited | Wholesale & retail | 2016 |
| Marinestore Limited | Wholesale & retail | 2010 |
| Marinestore Mailorder Limited | Wholesale & retail | 2012 |
| Maritime International Solutions (Insurance Brokers) Limited | Financial services | 2006 |
| Maritime International Solutions Limited | Financial services | 2008 |
| Maritime Pacific Insurance Services Limited | Financial services | 2001 |
| Marjoram Leisure Limited | Hospitality | 1995 |
| Marjoram Trading Limited | Hospitality | 2022 |
| Mark Beaver Surveying Services Limited | Construction | 2003 |
| Mark Identities Limited | Professional & scientific | 2011 |
| Mark Infra Services Ltd | Wholesale & retail | 2019 |
| Mark's Transportation Ltd | Transport & logistics | 2021 |
| MARK2 Developments (65B/C High Street) Ltd | Construction | 2019 |
| MARK2 Developments (Charles Cross) Ltd | Real estate | 2023 |
| MARK2 Developments (Hullbridge Road) Ltd | Construction | 2021 |
| MARK2 Developments (the Willows) Ltd | Real estate | 2017 |
| MARK2 Developments Ltd | Construction | 2019 |
| MARK2 Ltd | Real estate | 2024 |
| Marktx Limited | Professional & scientific | 2017 |
| Marlborough Highways Group Limited | Construction | 2013 |
| Marlborough Highways Limited | Construction | 1992 |
| Marlborough House (Chelmsford) Limited | Extraterritorial | 1999 |
| Marlborough House Partners LLP | | 2014 |
| Marlborough Mcdonald Ltd | Construction | 2015 |
| Marlow Medical Ltd | Health & social care | 2013 |
| Marlow Property Investments Limited | Real estate | 2019 |
| Marlow Surveying Services Limited | Professional & scientific | 2008 |
| Marmoset Digital Ltd | Information & communication | 2019 |
| Maroon Moon Ltd | Wholesale & retail | 2023 |
| Marquee Club Limited | Professional & scientific | 2013 |
| Marquee Records Limited | Information & communication | 2020 |
| Marriages Specialist Foods Limited | Manufacturing | 2012 |
| Marriotts Associates Limited | Professional & scientific | 2006 |
| Marriotts Business Services Limited | Administrative & support | 2003 |
| Marriotts Consultancy LLP | | 2008 |
| Marriotts Investments Limited | Real estate | 2005 |
| Marsden Active Limited | Arts & recreation | 2024 |
| Marsel Discount Home Store Ltd | Wholesale & retail | 2024 |
| Marsh and Hall Painters Limited | Construction | 2022 |
| Marsh Farm Day Nursery Limited | Health & social care | 2024 |
| Marsh Farm Group Limited | Financial services | 2024 |
| Marsh Farm Properties Limited | Real estate | 2024 |
| Marsh Metalworks Ltd | Construction | 2009 |
| Marshall Building Solutions Ltd | Construction | 2025 |
| Marston Vale Properties Ltd | Real estate | 2013 |
| Martin Carroll Construction Ltd | Construction | 2016 |
| Martin Financial Management Limited | Financial services | 2014 |
| Marvellousme Limited | Information & communication | 2013 |
| Mary Munnion Management Co Ltd | Construction | 2013 |