| M&S Sterling Ltd | Construction | 2018 |
| M&W Global Limited | Wholesale & retail | 2026 |
| M-Dog Ltd | Arts & recreation | 2023 |
| M-Imna Ltd | Real estate | 2016 |
| M. Hakimzada Ltd | Professional & scientific | 2026 |
| M.A.S Property Trading UK Ltd | Real estate | 2012 |
| M.B.I. Resources Limited | Transport & logistics | 2017 |
| M.C. Construction Equipment Limited | Manufacturing | 1995 |
| M.H.R. Agency Limited | Real estate | 2012 |
| M.S. Imagine Ltd | Construction | 2017 |
| M.S. Ventures Limited | Hospitality | 1997 |
| M21 Auto Ltd | Wholesale & retail | 2025 |
| M2H Management Ltd | Financial services | 2023 |
| MA Training Ltd | Education | 2024 |
| Maad Electricians' Contractor Limited | Construction | 2013 |
| Maan Builders Limited | Construction | 2012 |
| Maanica Limited | Information & communication | 2008 |
| Maars Telecom Ltd | Wholesale & retail | 2025 |
| Macclesfield Electrician Ltd | Construction | 2026 |
| Macovei Construction Limited | Construction | 2024 |
| Madang Limited | Hospitality | 2021 |
| Madecom Limited | Professional & scientific | 2013 |
| Madina Butchers (Shepherds Bush) Ltd | Wholesale & retail | 2014 |
| Madlinco Manufacturing Limited | Manufacturing | 2017 |
| Maendeleo CIC | Information & communication | 2019 |
| Maferuk Limited | Wholesale & retail | 2024 |
| Magdas FUN House Ltd | Health & social care | 2012 |
| Magel Construction Limited | Construction | 2017 |
| Maggie Greenford Station Fish & Chips Ltd | Hospitality | 2023 |
| Maggie Milosavljevic Ltd | Professional & scientific | 2024 |
| Magic Beauty Ltd | Other services | 2017 |
| Magic Coffee Expedition Ltd | Wholesale & retail | 2024 |
| Magic Flower TD Ltd | Wholesale & retail | 2026 |
| Magic LED Ltd | Construction | 2019 |
| Magnum Opus Enterprise Ltd | Transport & logistics | 2020 |
| Maha Mangalam Ltd | Wholesale & retail | 2017 |
| Mahayogi Siddhababa Spiritual Academy, UK | Health & social care | 2018 |
| Main Rock Services Limited | Construction | 2016 |
| Mainly Socials Ltd | Professional & scientific | 2023 |
| Maintenance Builders Ltd | Construction | 2025 |
| Maintenance for London Ltd | Construction | 2022 |
| Maison Zari Ltd | Manufacturing | 2025 |
| Malcolm Betts Limited | Manufacturing | 1996 |
| Malik & Co Realty Ltd | Real estate | 2024 |
| Mama Youth Project | Education | 2006 |
| Mama's Breakfast Club CIC | Education | 2026 |
| Mambo 4 FUN Ltd | Arts & recreation | 2023 |
| MAN Pharma Limited | Wholesale & retail | 2018 |
| Mandoo Limited | Wholesale & retail | 2013 |
| Mandziuk Constructions Ltd | Construction | 2015 |
| Maneco Holdings Limited | Financial services | 2023 |
| Manelight Limited | Real estate | 2023 |
| Mangal Homes Ltd | Extraterritorial | 2025 |
| Mangos Systems Limited | Professional & scientific | 2006 |
| Manish Ltd | Wholesale & retail | 2025 |
| Manomay International Ltd | Wholesale & retail | 2025 |
| Manor Gardens (Camelford) Management Company Ltd | Real estate | 2023 |
| Manpower Link Ltd | Administrative & support | 2025 |
| Manro Regeneration & Development Advisory Ltd | Construction | 2026 |
| Manzil Rentals Ltd | Real estate | 2024 |
| Maqbool Sons Autos Ltd | Wholesale & retail | 2017 |
| Maral Tours Ltd | Administrative & support | 2019 |
| Marble Arch Auto Accessories Limited | Wholesale & retail | 1998 |
| Marchanson Limited | Arts & recreation | 1972 |
| Marcus Cosmatic Ltd | Other services | 2017 |
| Marek Electrical Installation Ltd | Other services | 2015 |
| Margalla Health Limited | Health & social care | 2023 |
| MARGARET84 Ltd | Administrative & support | 2026 |
| Margarita Services Limited | Administrative & support | 2017 |
| Marhana Services & Trade Limited | Administrative & support | 2014 |
| Maria and Co Lawyers Ltd | Professional & scientific | 2025 |
| Marine Production Technology Limited | Professional & scientific | 2013 |
| Mario Clean Kingdom Ltd | Water & waste | 2023 |
| Mark Edge Ltd | Wholesale & retail | 2025 |
| Mark G Construction Limited | Construction | 2021 |
| Mark Milton Ltd | Wholesale & retail | 1991 |
| Market Hub Ltd. | Wholesale & retail | 2019 |
| Marketwise Properties Limited | Households | 1995 |
| Markoni Computing Limited | Information & communication | 2014 |
| Markoni Consulting Limited | Information & communication | 2015 |
| Markstone Construction (UK) Limited | Construction | 2008 |
| Markstone Properties Limited | Construction | 2014 |
| Marms London Limited | Hospitality | 2025 |
| Marron Civil Engineering Limited | Construction | 1987 |
| Marsa Professional Limited | Health & social care | 2017 |
| Marsda Limited | Wholesale & retail | 2018 |
| Marshal Events Limited | Hospitality | 2022 |
| Marshes Relief Firm (MRF) Limited | Extraterritorial | 2016 |
| Marszpol Construction Ltd | Construction | 2017 |
| Martingale Productions Limited | Information & communication | 2010 |
| Marut Trading Limited | Wholesale & retail | 2009 |
| Marvel Foods Limited | Wholesale & retail | 2024 |
| Maryam-Traders Ltd | Wholesale & retail | 2024 |
| Marys Deals Ltd | Wholesale & retail | 2020 |
| MAS Movement Ltd | Hospitality | 2024 |
| MAS Wheels Ltd | Wholesale & retail | 2020 |
| Mass IT Limited | Information & communication | 2014 |
| Masstex Build Limited | Construction | 2025 |
| Master Design Property Investments Limited | Real estate | 2022 |
| Master Glazing and Construction Ltd | Construction | 2026 |