| Mammoth Tools UK Ltd | Professional & scientific | 2015 |
| Mamute Ltd | Real estate | 2021 |
| Management Developments Limited | Information & communication | 2003 |
| Managereal Estates Ltd | Real estate | 2020 |
| Manda Garage Limited | Wholesale & retail | 2013 |
| Mandalai AI Solutions Ltd | Information & communication | 2026 |
| Mandarin Chef Poole Ltd | Hospitality | 2026 |
| Mandeville Road (Weymouth) Management Company Limited | Households | 2020 |
| Mandula Chelm Ltd | Transport & logistics | 2026 |
| Mang MEE Ltd | Hospitality | 2019 |
| Mangsam Ltd | Wholesale & retail | 2022 |
| Mangusta Management Ltd | Professional & scientific | 2018 |
| Mank T Ltd | Real estate | 2026 |
| Manka Limited | Information & communication | 2023 |
| Mann's Bookkeeping Limited | Professional & scientific | 2022 |
| Manna Enterprises Ltd | Wholesale & retail | 2022 |
| Manor Road (Swanage) Management Company Limited | Households | 2025 |
| Manor Security and Maintenance Solutions Ltd | Administrative & support | 2007 |
| Manorshore Limited | Real estate | 1999 |
| Mansfield Court Parkstone (Freehold) Limited | Households | 2000 |
| Manstyles Europe Limited | | 1963 |
| Manto Household Management Ltd | Professional & scientific | 2021 |
| Mapah Investments Ltd | Financial services | 2006 |
| Maple Communication Limited | Information & communication | 2008 |
| Maple Lodge Freehold Limited | Hospitality | 1995 |
| Maplebox Ltd | Wholesale & retail | 2025 |
| Mapp &Thread Ltd | Manufacturing | 2025 |
| MAR Store Ltd | Wholesale & retail | 2025 |
| Maracuya Ltd | Manufacturing | 2019 |
| Marageo Ltd | Construction | 2019 |
| Marang Limited | Wholesale & retail | 2002 |
| Maraval 2023 Ltd | Construction | 2023 |
| Maraval Holdings Ltd | Financial services | 2021 |
| Maraval Investments Ltd | Construction | 2016 |
| Maraval Segensworth Road Ltd | Construction | 2021 |
| Marbella Estates Limited | Real estate | 2023 |
| Marble & Granite Inspirations Limited | Manufacturing | 2006 |
| Marbyl Limited | Professional & scientific | 2025 |
| Marc Rhodes PT Limited | Other services | 2017 |
| Marcamax Limited | Administrative & support | 2021 |
| March Rose Property Limited | Real estate | 2017 |
| Marchcroft Limited | Other services | 2020 |
| Marco Home Improvements Limited | Construction | 2016 |
| Marcol Building and Property Limited | Construction | 2015 |
| Marcos Engineering Limited | Wholesale & retail | 2023 |
| Marcos Heritage Spares Limited | Wholesale & retail | 1999 |
| Marcos Motor Company Limited | Real estate | 1956 |
| Marcos Performance Limited | Wholesale & retail | 2006 |
| Marcos Racing Limited | Wholesale & retail | 1999 |
| Marcos Sales Limited | Wholesale & retail | 1962 |
| Mard Express Delivery Ltd | Transport & logistics | 2024 |
| Marden Soft Furnishings Limited | Manufacturing | 2018 |
| Mare Lupus Ltd | Other services | 2018 |
| Mare Robise Ltd | Real estate | 2010 |
| Mareel Aesthetics Ltd | Health & social care | 2025 |
| Marek Bobrowicz Ltd | Manufacturing | 2026 |
| Marengo Advisors Ltd | Professional & scientific | 2020 |
| Marff Limited | Real estate | 2013 |
| Margaret ANN Tierney Ltd | Extraterritorial | 2024 |
| Margaret Collins Limited | Real estate | 1996 |
| Margaret Rose Care Limited | Health & social care | 2004 |
| Margins Clothing Ltd | Wholesale & retail | 2025 |
| Margot ANN Tierney | Extraterritorial | 2024 |
| Maria.M Ltd | Health & social care | 2021 |
| Marian Close Management Limited | Extraterritorial | 2005 |
| Marianmit Trans Ltd | Transport & logistics | 2020 |
| Mariko London Ltd | Wholesale & retail | 2024 |
| Marina Properties (Castle Cary) Limited | Real estate | 2005 |
| Marina View Limited | Real estate | 2000 |
| Marine & General Services Limited | Professional & scientific | 2002 |
| Marine and Motorhome Interior Specialist Limited | Manufacturing | 2024 |
| Marine Composites & GRP Ltd | Manufacturing | 2019 |
| Marine Navigation Systems Ltd | Professional & scientific | 2022 |
| Marine Recycling Limited | Water & waste | 2019 |
| Marine Spares UK Ltd | Wholesale & retail | 2019 |
| Marine TEC Ltd | Manufacturing | 2019 |
| Mario's Solution Limited | Health & social care | 2018 |
| Mariotrans-Service Ltd | Wholesale & retail | 2025 |
| Mariposa International Ltd | Administrative & support | 2017 |
| Maritime Professional Development Dorset Ltd | Administrative & support | 2024 |
| Maritime Services Limited | Administrative & support | 1996 |
| Maritime Warranties Ltd. | Extraterritorial | 1993 |
| Marius&Darius Ltd | Transport & logistics | 2018 |
| Mariyam Foods Ltd | Wholesale & retail | 2025 |
| Mark Burstow Consultancy Limited | Professional & scientific | 2024 |
| Mark DH Ltd | Wholesale & retail | 2022 |
| Mark Ferns Group Ltd | Administrative & support | 2020 |
| Mark Kevin Miller Contractors Ltd | Construction | 2025 |
| Mark Walker Design and Project Management Ltd | Construction | 2015 |
| Mark Way Construction Ltd | Construction | 2022 |
| Mark Worboys Tree Surgery Limited | Agriculture & fishing | 2015 |
| Mark Zone SEO Ltd | Professional & scientific | 2024 |
| MARK4YOU Ltd | Professional & scientific | 2018 |
| Markelektro Ltd | Manufacturing | 2019 |
| Market Execution Ltd | Professional & scientific | 2021 |
| Market Sell Repeat Ltd | Information & communication | 2017 |
| Marketing and Leisure Management Limited | Arts & recreation | 2014 |
| Marketing GHM Ltd | Wholesale & retail | 2025 |
| Marketing Intelligence Online Limited | Financial services | 2014 |
| Marketingmadness Ltd | Information & communication | 2025 |