| Monarch Way RTM Company Limited | Households | 2024 |
| Monday Marketing Ltd | Professional & scientific | 2021 |
| Monday Travel Ltd | Administrative & support | 2022 |
| MONDAYTHE15TH Ltd | Administrative & support | 2023 |
| Mondelux Limited | Other services | 2024 |
| Mondy MOO Ltd | Wholesale & retail | 2020 |
| Money Matters (Bucks) Limited | Financial services | 2007 |
| Money Matters Education CIC | Education | 2025 |
| Montagnefin Ltd | Professional & scientific | 2019 |
| Montague Transport Limited | Transport & logistics | 2026 |
| Montesnowdon Limited | Professional & scientific | 2018 |
| Montgomery Coaching Limited | Administrative & support | 2014 |
| Montrose Holdings Limited | Wholesale & retail | 2015 |
| Moonlight Drive Limited | Arts & recreation | 2019 |
| Moonlit Travels Ltd | Administrative & support | 2018 |
| Moorepilates Limited | Education | 2010 |
| Moorfield Capital Limited | Financial services | 2024 |
| Moorwood Consultancy Ltd | Professional & scientific | 2012 |
| MOP & Bucket 2U Ltd | Administrative & support | 2017 |
| Morabor Ltd | Professional & scientific | 2019 |
| More Secured Limited | Construction | 2025 |
| More Than a Pill Ltd | Health & social care | 2022 |
| Moretti Automotive Limited | Wholesale & retail | 2013 |
| Morning Sunrise Limited | Professional & scientific | 2009 |
| Moroccan Glow Ltd | Wholesale & retail | 2021 |
| Moroccan Tagine Express Ltd | Manufacturing | 2025 |
| Morphic Studio Limited | Manufacturing | 2006 |
| Morriarti Photography & Design Ltd | Professional & scientific | 2016 |
| Morris and Shah Limited | Professional & scientific | 2009 |
| Morris Mair Limited | Administrative & support | 2016 |
| Morris Major Limited | Professional & scientific | 2012 |
| Mortgage Management Professionals Limited | Financial services | 2012 |
| Mortimer Photography Ltd | Professional & scientific | 2023 |
| Mortonjamesconsulting Ltd | Information & communication | 2018 |
| Morwenna Opie Ltd | Administrative & support | 2012 |
| Mosaic Surgical Limited | Manufacturing | 2016 |
| Mosaico Ltd | Wholesale & retail | 2016 |
| Mosqueapp Ltd | Information & communication | 2022 |
| Moss Construction Management Ltd | Construction | 2014 |
| MOT 123 Ltd | Wholesale & retail | 2012 |
| Motor Avenue Ltd | Other services | 2019 |
| Motor Haven HW Ltd | Wholesale & retail | 2026 |
| Motor Strada Limited | Wholesale & retail | 2023 |
| Motor Tech Recuritment Ltd | Wholesale & retail | 2016 |
| Motor Trend Ltd | Wholesale & retail | 2023 |
| Motorarc Ltd | Wholesale & retail | 2025 |
| Motortek Service Centre Ltd | Wholesale & retail | 2023 |
| Motus Group (UK) Limited | Wholesale & retail | 1960 |
| Motus Holdings (UK) Limited | Professional & scientific | 2005 |
| Mould Advisory Service Ltd. | Professional & scientific | 2008 |
| Mount Vezima Limited | Professional & scientific | 2016 |
| Mountain Music Group Ltd | Professional & scientific | 2020 |
| Mouse Systems Limited | Professional & scientific | 1984 |
| Move 2 Grow Holdings Ltd | Financial services | 2022 |
| Move 2 Grow Ltd | Real estate | 2018 |
| Move 2 Grow Sourcing Ltd | Real estate | 2022 |
| Move Space Living Limited | Real estate | 2025 |
| Moxham Property Ltd | Real estate | 2023 |
| MP Electrical, South East Ltd | Construction | 2015 |
| MP Marlow Limited | Hospitality | 2025 |
| MPC Property LLP | | 2016 |
| MPD Carpentry Ltd | Construction | 2026 |
| MPE Plastering Ltd | Construction | 2022 |
| MR Barber.Hw Ltd | Other services | 2025 |
| MR DEE Ltd | Wholesale & retail | 2025 |
| MR Drive Driving Limited | Education | 2025 |
| MR India Ltd | Hospitality | 2016 |
| MR Mcclean Ltd | Other services | 2022 |
| MR Packaging Ltd. | Wholesale & retail | 2011 |
| MR Services Hazlemere Limited | Wholesale & retail | 2011 |
| MR Wish Competitions Ltd | Arts & recreation | 2023 |
| MRB Heating and Plumbing Limited | Construction | 2015 |
| Mrbsa Ltd | Other services | 2025 |
| MRM Geotech Ltd | Professional & scientific | 2022 |
| MRS. Cleaning Ltd | Administrative & support | 2024 |
| MRV Construct Ltd | Construction | 2026 |
| MRW Aviation Ltd | Extraterritorial | 2019 |
| MS Audiology Services Ltd | Professional & scientific | 2016 |
| MS Autohub Ltd | Wholesale & retail | 2023 |
| MS Bizz Ltd | Wholesale & retail | 2024 |
| MS Development Holdings Limited | Real estate | 2021 |
| MS IT Consultancy Services Ltd | Information & communication | 2026 |
| MS Maintenance Solutions Limited | Other services | 2014 |
| MS Recruiters Ltd | Administrative & support | 2025 |
| MSB Carpentry Ltd | Construction | 2007 |
| Mscm Holdings Limited | Financial services | 2024 |
| Mscm Limited | Mining & quarrying | 1999 |
| Mscm Subsea Distribution Limited | Professional & scientific | 2024 |
| MSE Cartech Limited | Wholesale & retail | 2014 |
| MSE Homes Limited | Real estate | 2021 |
| MSL Graphics Ltd | Information & communication | 2004 |
| MSM 90 Limited | Wholesale & retail | 2023 |
| Mspacera Ltd | Real estate | 2026 |
| MSU Motors Ltd | Wholesale & retail | 2024 |
| MT Freight Services Ltd | Transport & logistics | 2014 |
| Mt-Seat Limited | Other services | 2019 |
| Mtaz Limited | Wholesale & retail | 2021 |
| Muck Away App International Limited | Construction | 2023 |
| Muck Away App UK Ltd | Construction | 2021 |
| Mucky Pups (G.X.) Limited | Other services | 2004 |