| Mandeleine Catering Ltd | Hospitality | 2023 |
| Mander Developments Limited | Real estate | 2010 |
| Mandeville Crescent Management Company Limited | Households | 2024 |
| Mandeville Promotions (Events) Limited | Arts & recreation | 2019 |
| Mandeville Promotions Limited | Arts & recreation | 2016 |
| Maneman Barbers Shop Limited | Other services | 2006 |
| Mangoe Developments Ltd | Construction | 2021 |
| Manners Hardware Ltd | Wholesale & retail | 2025 |
| Manor House (Lewes Road) Management Limited | Households | 2015 |
| Manor Metal Finishing Limited | Administrative & support | 1995 |
| Manor Work Surfaces Limited | Manufacturing | 2017 |
| Mantra Supplements Ltd | Hospitality | 2021 |
| Mantraraj Infotech Ltd | Wholesale & retail | 2010 |
| Manufacturing Services EBT Limited | Professional & scientific | 2019 |
| Manufacturing Services Investment Limited | Financial services | 2014 |
| Manya Ltd | Real estate | 2023 |
| Manz Global Ltd | Wholesale & retail | 2025 |
| Manzi Leisure Limited | Real estate | 1986 |
| MAP Education Finance & Support Services Limited | Education | 2012 |
| Maple Mollys Ltd | Manufacturing | 2025 |
| Maple Tree Surgery & Landscapes Limited | Administrative & support | 2004 |
| Maple.Ca Ltd | Wholesale & retail | 2020 |
| Mapleleaf Gardens Management Company Limited | Real estate | 1990 |
| MARBONYX1976 Limited | Manufacturing | 2020 |
| Mardin 47 Ltd | Hospitality | 2021 |
| Mardon Facilities Ltd | Real estate | 2005 |
| Margaret John Limited | Hospitality | 2018 |
| Maria & Danish Co Limited | Real estate | 2023 |
| Maria Moon Music CIC | Education | 2025 |
| Maria Smiles Limited | Administrative & support | 2012 |
| Mariana Pistol Consultancy Limited | Health & social care | 2019 |
| Marine Food Restaurant Limited | Hospitality | 2022 |
| Marine PUB Company Limited | Hospitality | 2024 |
| Mariner House RTM Company Limited | Households | 2021 |
| Marja Properties Limited | Real estate | 2016 |
| Mark Dean Wealth Management (UK) Limited | Financial services | 2014 |
| Mark in the Green Ltd | Administrative & support | 2012 |
| Mark Randall Limited | Wholesale & retail | 2011 |
| Market Search Limited | Administrative & support | 2009 |
| Markus Yoga Ltd | Health & social care | 2024 |
| Marli ROW Limited | Wholesale & retail | 2024 |
| Marshall Bull Ceramic Tiling Limited | Manufacturing | 1998 |
| Marshall Marketing Limited | Professional & scientific | 2022 |
| Martin & Moorey Group Ltd | Wholesale & retail | 2026 |
| Martin Anaesthetic Services Ltd | Health & social care | 2018 |
| Martin Higgs Ltd | Extraterritorial | 2024 |
| Martin Leslie Higgs Ltd. | Extraterritorial | 2024 |
| Martin-Wood Essential Group (UK) Limited | Financial services | 2024 |
| Marton Imaging Ltd | Wholesale & retail | 2006 |
| Mary V Limited | Professional & scientific | 2014 |
| MAS Consultancy Services Limited | Professional & scientific | 2016 |
| Masala Inn Ltd | Hospitality | 2019 |
| Mashie Care Services Ltd | Health & social care | 2025 |
| Masifa Group Ltd | Hospitality | 2022 |
| Mason Property Limited | Real estate | 2002 |
| Mathskairos Global Education Limited | Information & communication | 2026 |
| Matiney Medical Ltd | Health & social care | 2024 |
| Matt Roach Racing Ltd | Wholesale & retail | 2016 |
| Matt Walton Safety Solutions Limited | Professional & scientific | 2010 |
| Matthew Dear Foundation | Education | 2010 |
| Mattice Training Ltd | Professional & scientific | 2025 |
| Mauve Accountancy Limited | Financial services | 2007 |
| Mauve Financial Solutions Ltd | Financial services | 2017 |
| Mavent Consultancy Limited | Professional & scientific | 2022 |
| Mavin Recruitment Limited | Administrative & support | 2015 |
| Maxigain Investment Limited | Administrative & support | 2024 |
| Maxim Associates (UK) Ltd | Professional & scientific | 2015 |
| Maxus Services Limited | Administrative & support | 2017 |
| Maxx Waste Removals Services Ltd | Water & waste | 2026 |
| MAY Wong Limited | Arts & recreation | 2023 |
| Mayesbrook Manor Barking Management Limited | Households | 2009 |
| Mayfair and Bond Limited | Wholesale & retail | 2019 |
| Mayfair Clifton Ltd | Real estate | 2016 |
| Mayfields (South Kirkby) Management Company Limited | Households | 2012 |
| Mazara Ltd | Hospitality | 2025 |
| Mazenice Limited | Administrative & support | 1987 |
| Mazrreku Properties Ltd | Real estate | 2024 |
| Mccarthy Spinks LLP | | 2023 |
| Mcdonnell Building Services Limited | Construction | 2016 |
| Mcintyre Limited | Professional & scientific | 2024 |
| Mciver Limited | Wholesale & retail | 2021 |
| MCK Support Limited | Health & social care | 2025 |
| Mckinley Controls Ltd | Professional & scientific | 2014 |
| MCM1 Limited | Wholesale & retail | 2023 |
| MCO Essex Limited | Construction | 2018 |
| MCO Group Limited | Construction | 2020 |
| Mcod Consultancy Ltd | Professional & scientific | 2015 |
| MCS Design Solutions Ltd | Professional & scientific | 2017 |
| MCW Engineering Ltd. | Construction | 2016 |
| MD Consulting Engineers Ltd | Professional & scientific | 2015 |
| MDT3LTVMX Ltd | Wholesale & retail | 2025 |
| MDV Specialist Engineering Limited | Manufacturing | 2002 |
| MDW Wealth Limited | Financial services | 2026 |
| ME and Myself Limited | Other services | 2025 |
| Mead Professional Services Limited | Administrative & support | 2012 |
| Meaden Hill Serviced Accommodation Ltd | Hospitality | 2025 |
| Meadow View (Rollaston) Management Company Limited | Households | 2014 |
| Meads (NO.1) Residents Company Limited | Households | 2002 |
| Meca Developments Ltd | Real estate | 2025 |
| Mechai Limited | Information & communication | 2019 |