| Maudlynn Holdings Ltd | Construction | 2021 |
| Maurice Bruno Ltd | Professional & scientific | 2002 |
| Maverick Interiors Ltd | Wholesale & retail | 2019 |
| MAX Floor UK Ltd. | Manufacturing | 2015 |
| Maximus Property Investment Ltd | Real estate | 2020 |
| Mayfield Investments Ascot Limited | Health & social care | 2022 |
| Maysur Limited | Construction | 2002 |
| Maze Creative Concepts (UK) Limited | Manufacturing | 2010 |
| Mazechase Limited | Professional & scientific | 1986 |
| MBE & JE Limited | Financial services | 2019 |
| MC Together Solutions Ltd | Professional & scientific | 2016 |
| Mccormack Advisory Limited | Professional & scientific | 2024 |
| MCH Capital Limited | Hospitality | 2025 |
| Mckay Estate LLP | | 2008 |
| Mckay Estate Management Ltd | Real estate | 2011 |
| MCL Site Management Services Ltd | Other services | 2015 |
| Mclaren Raeside Ltd | Administrative & support | 2007 |
| MCW Construction Ltd | Construction | 2012 |
| MD Scenery Limited | Construction | 2022 |
| MDM Services Ltd | Professional & scientific | 2012 |
| Mead Gardens (Ascot) Management Company Limited | Households | 2017 |
| Mechon Limited | Professional & scientific | 2004 |
| Meddings Magic Location Company Ltd | Information & communication | 2016 |
| Media Control Room Ltd | Information & communication | 2025 |
| Mediatouch Limited | Information & communication | 2023 |
| Medicine and More Limited | Health & social care | 2022 |
| Meedhurst Project Management Limited | Professional & scientific | 2001 |
| Meesh Noor Ascot London Ltd | Manufacturing | 2026 |
| Melberry Consulting Limited | Administrative & support | 2011 |
| Mellinsus Renewables Limited | Professional & scientific | 2004 |
| Memart Ltd | Professional & scientific | 2018 |
| Memery Homes Ltd | Real estate | 2024 |
| Memises Ltd | Other services | 2021 |
| Menska Ltd | Administrative & support | 2012 |
| Meridian Meadow Estates Ltd | Real estate | 2026 |
| Mero-Schmidlin (UK) PLC | Construction | 1988 |
| Merryman Carpentry Ltd | Construction | 2025 |
| Meso Marketing Limited | Administrative & support | 2010 |
| Metaflight Limited | Information & communication | 2014 |
| Mexborough House RTM Company Limited | Households | 2025 |
| MFL Health Limited | Health & social care | 2021 |
| MGK Recruitment Limited | Administrative & support | 2023 |
| Michael Lynch Transport Limited | Transport & logistics | 2023 |
| Mick Doran Limited | Arts & recreation | 2018 |
| Microm Limited | Manufacturing | 1993 |
| Milkwood Capital Ltd | Financial services | 2013 |
| Milkwood Capital Management Holdings Ltd | Financial services | 2013 |
| Mill Ride Consulting Ltd | Professional & scientific | 2026 |
| Millden Holdings Limited | Professional & scientific | 2004 |
| Millers Image Limited | Professional & scientific | 2017 |
| Mimosa Interiors Limited | Wholesale & retail | 2018 |
| Mindcareworks Ltd | Education | 2023 |
| Minerva Accountants Ltd | Professional & scientific | 2021 |
| Minke Marine (UK) Ltd. | Extraterritorial | 2008 |
| Minna Quarters Limited | Real estate | 2021 |
| Minuta London Limited | Manufacturing | 2026 |
| Mitchel LEE LLP | | 2014 |
| MJ Project Solutions Ltd | Information & communication | 2015 |
| MK Direct Ltd | Wholesale & retail | 2024 |
| MK Food Safety Solutions Ltd | Professional & scientific | 2025 |
| Mk&T Analysis Limited | Administrative & support | 2012 |
| MLF Services Holdings Limited | Professional & scientific | 2025 |
| MN Global Limited | Information & communication | 2011 |
| Modena Interiors Limited | Wholesale & retail | 2023 |
| Modernism in Timeless Design Ltd | Professional & scientific | 2018 |
| Momentum Save Ltd | Real estate | 2008 |
| Moneglia Limited | Professional & scientific | 2010 |
| Monno Developments Ltd | Construction | 2022 |
| Monopoly Property Trading Ltd | Real estate | 2020 |
| Montañez Group Ltd | Hospitality | 2016 |
| Moobella Ltd. | Administrative & support | 2013 |
| Moonshot Eco Fuels Limited | Wholesale & retail | 2024 |
| Moonshot Operations Limited | Professional & scientific | 2016 |
| Moonshot Strategies Limited | Professional & scientific | 2019 |
| Morgan Nolan Ltd | Real estate | 2019 |
| Morgan Patrick Consulting Limited | Administrative & support | 2014 |
| Morning View Escapes Ltd | Administrative & support | 2024 |
| Morris Hartdene Limited | Professional & scientific | 2003 |
| Mossmead Estates Limited | Real estate | 2018 |
| Mossmead House Ltd | Real estate | 2023 |
| Mossvale Solutions Limited | Information & communication | 2025 |
| Motion Analysis Resource Systems Limited | Professional & scientific | 2008 |
| Motion for Life Limited | Arts & recreation | 2015 |
| Mount Securities Limited | Professional & scientific | 2003 |
| Moven Motion Ltd | Professional & scientific | 2026 |
| MR AJ Unwin - Medicolegal Limited | Health & social care | 2010 |
| Mrgc 2013 Ltd | Arts & recreation | 2013 |
| Mrjb Performance Ltd | Professional & scientific | 2010 |
| Msquared Industries Ltd | Extraterritorial | 2018 |
| MT Private Ltd | Wholesale & retail | 2025 |
| MTM Data Research Ltd | Information & communication | 2022 |
| Musangu Foundation | Health & social care | 2015 |
| Musgrove Piano Tuning Limited | Other services | 2010 |
| Mustard PR Ltd | Professional & scientific | 1999 |
| Muven Ltd | Information & communication | 2022 |
| MV Films Ltd | Information & communication | 2013 |
| MV Southern Ltd | Construction | 2019 |
| MWE Services Ltd | Construction | 2017 |
| My Life Fit Limited | Health & social care | 2014 |
| My Plan B Ltd | Real estate | 2017 |