| Morello Bookings Ltd | Other services | 2017 |
| Moreton Lane Cottages Limited | Households | 2005 |
| Moreton Properties LLP | | 2022 |
| Morgan Dwyer Limited | Wholesale & retail | 2014 |
| Morgan House Investments Ltd | Real estate | 2024 |
| Moria & Oscar Ltd | Information & communication | 2015 |
| Morko Limited | Information & communication | 2018 |
| Morland Group Ltd | Water & waste | 2025 |
| Morning Mist Publications Ltd | Other services | 2021 |
| Morphai Limited | Information & communication | 2025 |
| Morrison Aesthetic Restorations Limited | Health & social care | 2007 |
| Morsli Solar Ltd | Other services | 2025 |
| Morton Management LLP | | 2006 |
| Morton Manufacturing Limited | Manufacturing | 2010 |
| Morton Wireless Limited | Information & communication | 2013 |
| Morty Scenery Ltd | Information & communication | 2025 |
| Morvan & Noel Ltd | Manufacturing | 1995 |
| Mossley Hill Childcare Limited | Administrative & support | 2006 |
| Mossyard Ltd | Real estate | 2001 |
| Mosu 2018 Ltd | Transport & logistics | 2018 |
| Motaline Workshop Supplies Ltd | Wholesale & retail | 2011 |
| Motion MIX Ltd | Wholesale & retail | 2026 |
| Motorguard Warranties Ltd | Wholesale & retail | 2021 |
| Motormavericks Performance Ltd | Wholesale & retail | 2024 |
| Motorstep Global Mobility Ltd | Manufacturing | 2017 |
| Motts Coaches (Aylesbury) Limited | Transport & logistics | 1975 |
| Motts Leisure Limited | Administrative & support | 1994 |
| Moulino PMC Ltd | Professional & scientific | 2015 |
| Mount Sinai Consultants Ltd | Professional & scientific | 2012 |
| Mountain Range Group Ltd | Financial services | 2026 |
| Mountford Croft Limited | Professional & scientific | 2013 |
| Mounthill Limited | Real estate | 1997 |
| Movement Auto Services Limited | Extraterritorial | 2000 |
| Movieglu Ltd | Information & communication | 2014 |
| MP Developmentz Ltd | Real estate | 2019 |
| MP Motorsportz Limited | Wholesale & retail | 2007 |
| MPC Cloud Consulting Limited | Information & communication | 2025 |
| MPI MIX Haulage Ltd | Transport & logistics | 2019 |
| MPL Technology Group Holdings Limited | Information & communication | 2017 |
| MPM Worldwide Limited | Manufacturing | 2008 |
| MR Maintenance Limited | Other services | 2017 |
| MR Make IT Happen Ltd | Administrative & support | 2025 |
| MR Power Ltd | Construction | 2023 |
| MR Saroe Ltd | Information & communication | 2014 |
| MR Speed London Ltd | Wholesale & retail | 2026 |
| Mrembo Linen Limited | Hospitality | 2025 |
| MRH Construct Limited | Construction | 2022 |
| MRH Track Limited | Construction | 2018 |
| MRS Casey Music Limited | Arts & recreation | 2011 |
| MS Infotech Ltd. | Information & communication | 2013 |
| MS Pro Plumbing and Heating Ltd | Construction | 2026 |
| MS Software Testing Limited | Information & communication | 2021 |
| MS4 Consultancy Ltd | Professional & scientific | 2025 |
| Msak Construction Limited | Construction | 2025 |
| MSJ1 Healthcare Limited | Health & social care | 2015 |
| MSK Services Bucks Ltd | Public administration | 2024 |
| Mskd Global Ltd | Professional & scientific | 2026 |
| Mslm Limited | Information & communication | 2024 |
| MSN Delivery Ltd | Transport & logistics | 2022 |
| MSP Vehicle Logistics Ltd | Transport & logistics | 2023 |
| MSS Consulting Services Ltd | Information & communication | 2024 |
| MTS Automotive Limited | Wholesale & retail | 2025 |
| MU Bathrooms Ltd | Construction | 2023 |
| MU Plumbing and Heating Ltd | Construction | 2021 |
| MU Property Ltd | Real estate | 2023 |
| Muddy Boots Consulting Ltd | Professional & scientific | 2023 |
| Muddy Nurseries Group Limited | Health & social care | 2021 |
| Muddy Puddles Nurseries Ltd | Education | 2020 |
| Muddy Puddles Property Limited | Households | 2021 |
| Muddy Stilettos Limited | Information & communication | 2014 |
| Muddy Sunshine Ltd | Education | 2022 |
| Muhimbi Ltd | Information & communication | 2008 |
| Mukie Financial Limited | Professional & scientific | 2024 |
| Mukis Fried Chicken Limited | Hospitality | 2017 |
| Mukzig Limited | Health & social care | 2026 |
| Mulberry Garden Rooms Ltd | Administrative & support | 2025 |
| Mullenbach Contractors Ltd | Professional & scientific | 2024 |
| Multifix Construction & Carpentry Ltd | Construction | 2023 |
| Mundy's Farm Residents' Association Limited | Households | 1988 |
| Mungo Laurence Ltd | Professional & scientific | 2015 |
| Munshi Communications Limited | Information & communication | 2016 |
| Muntenias Resturant Limited | Hospitality | 2025 |
| Murder Mystery Club Ltd | Information & communication | 2025 |
| Murrock Properties Ltd | Real estate | 2025 |
| Murtagh Demolition Limited | Construction | 2007 |
| Museba Homecare Limited | Real estate | 2014 |
| Musk Hill Consulting Limited | Professional & scientific | 2021 |
| Muswell Manufacturing Co. Limited | Wholesale & retail | 1975 |
| Mutaf Car Parts Limited | Wholesale & retail | 2022 |
| Mutch Plastering Ltd | Construction | 2026 |
| Muzamic Ltd | Wholesale & retail | 2024 |
| MVB IT Services Ltd | Information & communication | 2026 |
| MVM Assets Limited | Real estate | 2022 |
| MVP Consultants Limited | Information & communication | 2024 |
| MVP Investments Limited | Real estate | 2024 |
| MW Building, Design & Consulting Ltd | Construction | 2024 |
| MW Coaching and Consulting Limited | Administrative & support | 2017 |
| MW Fire Ltd | Construction | 2009 |
| MW Football Coaching Ltd | Arts & recreation | 2022 |
| MW Jones Consulting Limited | Professional & scientific | 2024 |