| M H Joinery Products Limited | Manufacturing | 1994 |
| M J Allen & Associates Limited | Professional & scientific | 2017 |
| M J Eyewear Limited | Extraterritorial | 2012 |
| M L Optics Limited | Health & social care | 2016 |
| M Luca Limited | Construction | 2017 |
| M Press (Media) Limited | Manufacturing | 2000 |
| M Press (Sales) Limited | Manufacturing | 1990 |
| M Rodrigues HGV Ltd | Transport & logistics | 2024 |
| M Satunas Ltd | Construction | 2019 |
| M&M Services (London) Ltd | Wholesale & retail | 2019 |
| M&N Toro Ltd | Financial services | 2026 |
| M&R Capital LLP | | 2012 |
| M&V Plus Ltd | Real estate | 2022 |
| M.C.C. Developments Limited | Construction | 1962 |
| M.E. Concept House Limited | Construction | 2010 |
| M.M. Parker Limited | Wholesale & retail | 2004 |
| M2S Scaffolding Ltd | Construction | 2025 |
| Maavelus Ltd | Information & communication | 2025 |
| Maax Ventures Ltd | Wholesale & retail | 2023 |
| Macber Ltd | Information & communication | 2021 |
| Machesney & Easty Management Ltd | Health & social care | 2012 |
| Macks Road (London) Residents Management Company Limited | Households | 2021 |
| Macro Ltd | Transport & logistics | 2022 |
| Madingley Mulch Limited | Professional & scientific | 1996 |
| MAG Accountants Limited | Professional & scientific | 2012 |
| Mag.W.F Ltd | Education | 2023 |
| Magee Bespoke Services Limited | Professional & scientific | 2021 |
| Magic Blue Sky Ltd | Construction | 2010 |
| Magic Hands Decorators Limited | Construction | 2021 |
| Magic Kids Ltd | Education | 2007 |
| Magic Mouse Design LLP | | 2016 |
| Magical Kitchens, Bathrooms and Bedrooms Ltd | Construction | 2021 |
| Magiclean by Vikky Ltd | Administrative & support | 2022 |
| Magnet Management Ltd | Real estate | 2014 |
| Maguire & Sharkey Properties (UK) Limited | Real estate | 2026 |
| MAI Tech Trade Ltd | Wholesale & retail | 2021 |
| Maidenhead ALE & Cider Investments Limited | Hospitality | 2020 |
| Main Computer Services Limited | Extraterritorial | 2004 |
| Maisons D'Amour International Limited | Education | 2025 |
| Maja Real Estate Limited | Financial services | 2022 |
| MAK 97 Ltd | Information & communication | 2019 |
| Make Your Looks Limited | Wholesale & retail | 2024 |
| Makeup Box Academy Ltd | Other services | 2023 |
| Makeup Box Studio Ibiza Ltd | Other services | 2023 |
| Makeval Limited | Construction | 1991 |
| MAL (2) Limited | Administrative & support | 2023 |
| Mala Designs Limited | Professional & scientific | 1981 |
| Mala Electrical Limited | Construction | 1980 |
| Mala Engineering Limited | Construction | 1971 |
| Mala Investments Limited | Professional & scientific | 1980 |
| Mala Maintenance Limited | Manufacturing | 1980 |
| Mala Management Limited | Professional & scientific | 1990 |
| Mala Mechanical Services Limited | Construction | 1984 |
| Mala Special Works Limited | Construction | 1980 |
| Malic Transports Ltd | Transport & logistics | 2021 |
| Malik Catering Ltd | Hospitality | 2014 |
| Malling Repair Services Limited | Wholesale & retail | 2012 |
| Mamta Saha Ltd | Other services | 2018 |
| Manaia & BO Limited | Wholesale & retail | 2024 |
| Manaton Limited | Construction | 1986 |
| Manic Motorz Ltd | Wholesale & retail | 2024 |
| Manns Management Ltd | Professional & scientific | 2022 |
| Manns Properties (Essex) Limited | Hospitality | 2009 |
| Manns Skip Hire Ltd | Water & waste | 2023 |
| Manny's Gardening Services Ltd | Arts & recreation | 2024 |
| Mano & Co International Limited | Wholesale & retail | 2020 |
| Mano Art Ltd | Construction | 2013 |
| Manor Court (Chingford) Management Company Limited | Households | 1992 |
| Manor Landscapes Epping Limited | Administrative & support | 2015 |
| Mansell Street Carpark Limited | Transport & logistics | 2002 |
| Mansfield PJ Limited | Hospitality | 2016 |
| Manufest Ltd | Professional & scientific | 2014 |
| Mapera Ltd | Wholesale & retail | 2026 |
| Maple Gate NO.2 Residents Company Limited | Households | 1989 |
| Marandar Tech Ltd | Information & communication | 2024 |
| March Land and Property Management LLP | | 2010 |
| Marcos Construction Limited | Construction | 2010 |
| Marcus Meats Limited | Wholesale & retail | 2024 |
| Margarlit Limited | Wholesale & retail | 2020 |
| Marigo Trading Limited | Wholesale & retail | 2012 |
| Marine Parade Property Investments Limited | Real estate | 2014 |
| Mario Constantinou Ltd | Other services | 2016 |
| MARIO-1 Ltd | Construction | 2007 |
| Maritos Services Limited | Information & communication | 2024 |
| Marius 88 & Co Ltd | Construction | 2015 |
| Marj Estates Limited | Real estate | 2012 |
| Marjan Fashion Limited | Wholesale & retail | 2023 |
| Mark a. Andrews Limited | Professional & scientific | 2016 |
| Mark Bassenger Limited | Administrative & support | 2003 |
| Mark Davall Motorcycles Limited | Wholesale & retail | 2004 |
| Markall Machines Limited | Manufacturing | 1959 |
| Market Road Property Limited | Real estate | 2018 |
| Marlol Ltd | Professional & scientific | 2025 |
| Marrev Management Limited | Households | 1965 |
| Marsden Fire and Risk Consultancy Limited | Professional & scientific | 2016 |
| Marshall Hall Limited | Professional & scientific | 2025 |
| Martac London Ltd | Wholesale & retail | 2024 |
| Martaka Construction Ltd | Construction | 2016 |
| Marvico Properties Ltd | Real estate | 2021 |
| Marwell Building Ltd | Real estate | 2025 |