| Muckrs Ltd | Water & waste | 2020 |
| Mucky Pups (Yorkshire) Ltd | Other services | 2017 |
| MUD Group Ltd | Construction | 2020 |
| MUD Monsterz Ltd | Wholesale & retail | 2026 |
| Muddy Buddies Ltd | Health & social care | 2023 |
| Muddy Faces Ltd | Manufacturing | 2006 |
| Muddy Feathers Ltd | Real estate | 2024 |
| Mudfords Limited | Manufacturing | 1991 |
| Mugenso Ltd | Information & communication | 2024 |
| Muhammad Sufyan Ltd | Wholesale & retail | 2025 |
| Muhammad Yousuf Chachar Ltd | Wholesale & retail | 2025 |
| MUK Distributions Ltd | Wholesale & retail | 2026 |
| Muk&M Ltd | Hospitality | 2025 |
| Mukabo Road Safety | Education | 2015 |
| Mukhawar Dudi Limited | Wholesale & retail | 2025 |
| Mukunzi H&T Ltd | Health & social care | 2015 |
| Mulberry Health Limited | Health & social care | 2009 |
| Mulch. Limited | Wholesale & retail | 2020 |
| Mulcroft Limited | Hospitality | 1989 |
| Mullen-Hicks Ltd | Professional & scientific | 2023 |
| Mullock Accountancy Limited | Professional & scientific | 2025 |
| Multi Construction Limited | Construction | 2017 |
| Multi Fabrications Limited | Manufacturing | 2017 |
| Multi Social Media Ltd | Professional & scientific | 2012 |
| Multi Sourcing Trading (UK) Ltd | Wholesale & retail | 2017 |
| Multi Waste Recycling Limited | Water & waste | 2014 |
| Multi Waste Skip Hire Limited | Water & waste | 2013 |
| Multi-Skilled Professionals Limited Limited | Administrative & support | 2013 |
| Multi-Therm Insulations Ltd | Professional & scientific | 2017 |
| Multi-Therm Ltd | Manufacturing | 2011 |
| Multijet Hardening Limited | Professional & scientific | 1977 |
| Multiple Store Ltd | Wholesale & retail | 2024 |
| Multitex Limited | Wholesale & retail | 2021 |
| Multiway Express Limited | Transport & logistics | 2014 |
| MUM Matters CIC | Health & social care | 2025 |
| Mummy's Dirty Laundry Ltd | Wholesale & retail | 2025 |
| Munaayyy Limited | Education | 2023 |
| Munch Records Ltd | Information & communication | 2020 |
| Munchies Barn Limited | Hospitality | 2025 |
| Munchies Corporation Limited | Hospitality | 2020 |
| MUNCHIES4 Limited | Hospitality | 2023 |
| Mundells Building & Renovation Ltd | Construction | 2023 |
| Mundojumbo Ltd | Professional & scientific | 2009 |
| Munro Architecture + Design Ltd | Professional & scientific | 2026 |
| Munro Homes and Property Ltd | Real estate | 2026 |
| Munroe Vehicle Sales Ltd | Wholesale & retail | 2023 |
| Munzara Limited | Health & social care | 2022 |
| Muqaideh Ltd | Transport & logistics | 2025 |
| Murais & IBB Ltd | Wholesale & retail | 2026 |
| Muraqabah Training Academy Ltd | Health & social care | 2026 |
| Muras Joinery and Property Renovation Ltd | Construction | 2025 |
| Murataj Ltd | Construction | 2026 |
| Murbek Holdings Limited | Financial services | 2022 |
| Murford Homes Ltd | Households | 2005 |
| Murpak Limited | Wholesale & retail | 1992 |
| Murphy Comhire Limited | Information & communication | 1972 |
| Murphy Investments Limited | Financial services | 2017 |
| Murphy PUB Co Ltd | Hospitality | 2024 |
| Murphy's Law Music Limited | Information & communication | 2023 |
| Murray and Freedom Investments Limited | Real estate | 2015 |
| Murray Road Partners Limited | Real estate | 2018 |
| Murray Webster Quality Meats Limited | Wholesale & retail | 2005 |
| Musa and Uzair Travels Ltd | Transport & logistics | 2025 |
| Musa Travels Ltd | Transport & logistics | 2025 |
| Musaid 2 Limited | Wholesale & retail | 2022 |
| Muscle Empire Ltd | Arts & recreation | 2016 |
| Muscle Fusion Gym Limited | Arts & recreation | 2019 |
| Muscle Fusion Shop & Fitness Ltd | Wholesale & retail | 2022 |
| Muse Escapes (Buxton) Limited | Construction | 2021 |
| Muse Escapes (Castleton) Limited | Hospitality | 2021 |
| Muse Homes Limited | Construction | 2017 |
| Musenuk Limited | Wholesale & retail | 2015 |
| Musgrave Analytics Ltd | Information & communication | 2011 |
| Musgrave Media Ltd | Information & communication | 2022 |
| Mushantech Limited | Wholesale & retail | 2025 |
| Musharaf Taxi Ltd | Transport & logistics | 2026 |
| Music and the Deaf | Health & social care | 1990 |
| Music by Numbers Limited | Financial services | 2020 |
| Music F.R. Co Ltd | Information & communication | 2017 |
| Music in the Round Limited | Arts & recreation | 1985 |
| Music Industry Therapists Limited | Health & social care | 2019 |
| Music Junkee Limited | Wholesale & retail | 2009 |
| Music Live Limited | Hospitality | 2021 |
| Music Matters Courses Limited | Education | 2019 |
| Music Mist Limited | Administrative & support | 2023 |
| Music Sounds Better With HUW Limited | Information & communication | 2009 |
| Music X Film Ltd | Information & communication | 2016 |
| Musicone Limited | Professional & scientific | 2019 |
| Musketeer Developments Ltd | Real estate | 2025 |
| Muslim Padel Limited | Arts & recreation | 2025 |
| Must & Lees Ltd | Wholesale & retail | 2021 |
| Mustafa&Bradford Ltd | Hospitality | 2025 |
| Mustang Hydroheat Ltd | Construction | 2025 |
| Mustbebuilt.Com Limited | Other services | 2011 |
| Mustec Ltd | Education | 2018 |
| Musty Food Services Ltd | Hospitality | 2024 |
| Mutlu Ltd | Real estate | 2019 |
| Mutoscope Films Limited | Arts & recreation | 2015 |
| Muttley Investments Ltd | Hospitality | 2022 |
| Muttzgonutz Ltd | Other services | 2025 |