| Marshall Scott Limited | Administrative & support | 2014 |
| Marshall's Property Solutions Limited | Construction | 2012 |
| Martcare Limited | Professional & scientific | 1983 |
| Martect Limited | Professional & scientific | 2020 |
| Martian Refurbishment Services Ltd | Manufacturing | 2017 |
| Martin & Martin Business Services Limited | Professional & scientific | 2002 |
| Martin and Manifold Vets Ltd | Professional & scientific | 2021 |
| Martin Commercial Properties Limited | Real estate | 2010 |
| Martin Docking Limited | Health & social care | 2000 |
| Martin Gilder Group Limited | Manufacturing | 2015 |
| Martin O'Connor Ltd | Administrative & support | 2017 |
| Martina Security & Cleaning Ltd | Other services | 2025 |
| Martins Meats Ltd | Wholesale & retail | 2026 |
| Martistry Limited | Arts & recreation | 2015 |
| Marton Arms Limited | Hospitality | 2017 |
| Martyn Powell Landscapes Limited | Administrative & support | 2014 |
| Marvellous Cleaning Solutions Ltd | Administrative & support | 2024 |
| Marvellous PUB Co. Ltd | Hospitality | 2024 |
| Mary Rush Care Homes Limited | Health & social care | 2012 |
| Mary Rush Care Limited | Health & social care | 2012 |
| Marylebone Group Ltd | Real estate | 2025 |
| MAS Emprise Ltd | Professional & scientific | 2025 |
| MAS Group Holdings Ltd | Professional & scientific | 2015 |
| Masala MOB Ltd | Hospitality | 2025 |
| Masaq Investments Limited | Financial services | 2021 |
| Mascof Design and Development Ltd | Administrative & support | 2022 |
| Mashbros Ltd | Hospitality | 2025 |
| Masito Limited | Financial services | 2021 |
| Mason Munro Medical Limited | Health & social care | 2013 |
| Mason Street Construction Limited | Construction | 2020 |
| Massey Medical Limited | Health & social care | 2026 |
| Massive Records Company Limited | Wholesale & retail | 2004 |
| Masta Properties Ltd | Real estate | 2019 |
| Mastermain Limited | Wholesale & retail | 2012 |
| Mastermind Translations Ltd | Professional & scientific | 2015 |
| Masterpiece Interiors Limited | Construction | 2011 |
| Matards Holding Limited | Financial services | 2024 |
| Matb Limited | Information & communication | 2011 |
| Match Fit Performance Ltd. | Professional & scientific | 2018 |
| Matchmymood Ltd | Information & communication | 2026 |
| Matchriver Analysis Limited | Information & communication | 1989 |
| Matchriver Intellectual Property Rights Limited | Information & communication | 2008 |
| Matedco Ltd | Professional & scientific | 2017 |
| Mathlin Building Solutions Ltd. | Construction | 2017 |
| Matopos Holdings Ltd | Financial services | 2025 |
| Matrix Clinics Group Limited | Health & social care | 2021 |
| MATRIX7 Ltd | Education | 2003 |
| Matt BEE Ltd | Real estate | 2017 |
| Matt Garrett Limited | Information & communication | 2003 |
| Matt Johnson Ltd. | Administrative & support | 2008 |
| Matt Lock Service Management Consultancy Limited | Information & communication | 2007 |
| Matt Rawlinson Design Limited | Professional & scientific | 2004 |
| Matt Smith-Wood Ltd | Professional & scientific | 2025 |
| Matt Went Plastering Ltd | Construction | 2018 |
| Matternet UK Ltd | Transport & logistics | 2025 |
| Matthaniel Corporation Limited | Professional & scientific | 2020 |
| Matthew Donovan Consulting Limited | Information & communication | 2024 |
| Matthew James Wilson Limited | Information & communication | 2023 |
| Matthew LUE Database Consulting Limited | Information & communication | 2025 |
| Matthew Shaw Ltd | Health & social care | 2010 |
| Matthew Wigan Associates Ltd | Professional & scientific | 2014 |
| Matthews Landscapes Limited | Construction | 2006 |
| Matts Monitors Limited | Manufacturing | 2013 |
| Mattvenbarbering Ltd | Other services | 2025 |
| Maudlin Street (Bristol) Management Limited | Real estate | 1985 |
| Maugersbury Consulting LLP | | 2024 |
| MAV Systems Limited | Professional & scientific | 2007 |
| Maverick 51 Ltd | Professional & scientific | 2018 |
| Maverick Digital Shop Ltd | Wholesale & retail | 2025 |
| Maverick Mill Limited | Manufacturing | 2025 |
| MAX Comley Racing Ltd | Arts & recreation | 2019 |
| MAX Driving Services Ltd | Transport & logistics | 2022 |
| MAX Your Potential Limited | Arts & recreation | 2024 |
| Maxiphi Limited | Extraterritorial | 2004 |
| Maxlet Property Solutions Limited | Real estate | 2016 |
| Maxthemaths Limited | Education | 2012 |
| MAY Investments Limited | Financial services | 2026 |
| Maya Mushrooms Ltd | Agriculture & fishing | 2018 |
| Maya&Andra Ltd | Hospitality | 2024 |
| Mayaroo Ltd | Wholesale & retail | 2026 |
| Maybank Land Limited | Financial services | 2017 |
| Mayday Seals & Bearings Ltd | Manufacturing | 2017 |
| Mayfair Heritage Ltd | Professional & scientific | 2024 |
| Mayfair Rise Ltd | Professional & scientific | 2018 |
| Maynard Engines Limited | Manufacturing | 2010 |
| MAZ Essentials Ltd | Wholesale & retail | 2026 |
| MAZ Global Market Ltd | Wholesale & retail | 2021 |
| Maze Workplace Limited | Professional & scientific | 2016 |
| Mazy PVT Ltd | Professional & scientific | 2011 |
| MB Break Limited | Hospitality | 2025 |
| MB Fashion Ltd | Wholesale & retail | 2020 |
| MB Finishings Ltd | Manufacturing | 2019 |
| MB Geologist Co Limited | Mining & quarrying | 2015 |
| MB Global Partners Limited | Professional & scientific | 2026 |
| MB Marketing Ltd | Professional & scientific | 2022 |
| Mb&B Ltd | Wholesale & retail | 2015 |
| MBR Holdings Limited | Financial services | 2009 |
| MC Gardens and Landscapes Ltd | Administrative & support | 2025 |
| MC Manus Ventures Limited | Hospitality | 2018 |
| MC Star Ltd | Other services | 2018 |