| MLR Events Limited | Administrative & support | 2023 |
| MM Paediatrics Limited | Health & social care | 2025 |
| MMM Consultancy Limited | Professional & scientific | 2006 |
| MMN Group Ltd | Transport & logistics | 2019 |
| Mmrg Transport Ltd | Transport & logistics | 2025 |
| MMW Property Solutions Ltd | Construction | 2026 |
| Mmwh Group Ltd | Wholesale & retail | 2023 |
| Mnop Ltd | Information & communication | 2012 |
| MNZ2 Ltd | Health & social care | 2015 |
| Moart-Uk Company Limited | Real estate | 2025 |
| Mobile Glass and Glazing Limited | Construction | 2011 |
| Moda IT Outlet Ltd | Wholesale & retail | 2022 |
| Mode Intra Ltd | Other services | 2017 |
| Modular BP Management Company Limited | Real estate | 2016 |
| Modular Solar Limited | Manufacturing | 2012 |
| Modus Transformation Communications Limited | Information & communication | 2021 |
| Moella's Touch Ltd | Administrative & support | 2025 |
| Mohaci Studios Limited | Information & communication | 2025 |
| Molecular Graphics and Modelling Society | Other services | 2004 |
| Molgen UK Ltd | Wholesale & retail | 2021 |
| Molla Consultancy Ltd | Professional & scientific | 2026 |
| Molxshop Limited | Manufacturing | 2025 |
| Moncow Productions Ltd | Information & communication | 2019 |
| Monlaw Limited | Wholesale & retail | 2025 |
| Monopizzeria Ltd | Hospitality | 2022 |
| Montel Coker Ltd | Administrative & support | 2025 |
| Montfleur Partners Ltd | Professional & scientific | 2022 |
| Moodley SA Limited | Other services | 2019 |
| Moodvent Limited | Households | 1988 |
| Moolah Matters Bookkeeping Limited | Professional & scientific | 2023 |
| Moolah Matters Holdings Limited | Financial services | 2023 |
| Moolah Matters Limited | Professional & scientific | 2019 |
| Moolah Matters Payroll Limited | Professional & scientific | 2023 |
| Moolah Matters Strategic Services Limited | Professional & scientific | 2025 |
| Moolah Matters Tax Services Limited | Professional & scientific | 2021 |
| Moore Fire Protection Ltd | Administrative & support | 2021 |
| Moore Interiors (Herts) Limited | Construction | 2018 |
| Moore Perfect Pieces Ltd | Wholesale & retail | 2019 |
| Mooresafe Environmental Ltd | Construction | 2026 |
| Moosib Services Limited | Real estate | 2025 |
| Moovshack Limited | Other services | 2017 |
| Mopay Limited | Other services | 2023 |
| Mopro Logistics Ltd | Transport & logistics | 2026 |
| Moraf Ventures Ltd | Professional & scientific | 2022 |
| Morne & Albion Holdings Ltd | Financial services | 2025 |
| Morris Newman Consulting Ltd | Other services | 2019 |
| Mortgage Hunters Homes Limited | Real estate | 2025 |
| Mortgagehunters Limited | Financial services | 2006 |
| Mostino Ltd | Hospitality | 2025 |
| Motcomb Lofts Limited | Construction | 2009 |
| Motlib Group Ltd | Households | 2023 |
| Mountain Healthcare Holdings Limited | Financial services | 2015 |
| Mountain Healthcare Limited | Health & social care | 2005 |
| Mountshannon Property Investments Limited | Real estate | 2021 |
| Mouths Motor Company Ltd | Wholesale & retail | 2018 |
| Movement in Motion Ltd | Other services | 2026 |
| Moyin & Dami Company Limited | Health & social care | 2018 |
| MPA London Limited | Professional & scientific | 2023 |
| MPE3 Ltd | Real estate | 2021 |
| MR D Green Limited | Construction | 2020 |
| MR Fixer Construction Ltd | Construction | 2025 |
| MR Sparkle Limited | Other services | 2006 |
| MR Spud Catering Ltd | Hospitality | 2023 |
| MRB Refurbishments and Extensions Ltd | Construction | 2025 |
| MRB Roofing Ltd | Construction | 2011 |
| MRM Disney Mechanic Ltd | Manufacturing | 2018 |
| Mrpd Limited | Wholesale & retail | 2022 |
| Msapeters Limited | Manufacturing | 2015 |
| MSB International Ltd | Wholesale & retail | 2015 |
| Mseb Services Ltd | Information & communication | 2014 |
| Msi-Uk Limited | Professional & scientific | 2026 |
| MSM Group Developments Ltd | Real estate | 2025 |
| Msmd Construction Ltd | Construction | 2018 |
| MSR Clinical Limited | Other services | 2017 |
| MSR Lettings Ltd | Real estate | 2023 |
| MSR Rental Ltd | Real estate | 2022 |
| MSR Renting Ltd | Real estate | 2025 |
| Mss-Ro Limited | Wholesale & retail | 2025 |
| Mstheatres Ltd | Health & social care | 2025 |
| MTG Lighting Ltd | Professional & scientific | 2023 |
| Mtravel-Solutions Ltd | Administrative & support | 1995 |
| MTS Contracting Limited | Construction | 2013 |
| MTS Creative Limited | Arts & recreation | 2024 |
| MUD Films Ltd | Information & communication | 2022 |
| Mullach Construction Ltd | Construction | 2018 |
| Mullnex Limited | Hospitality | 2014 |
| Multi-Care Community Services East & West Hertfordshire Ltd | Health & social care | 2023 |
| Multiple Consulting Limited | Professional & scientific | 2023 |
| Multiple Group Holding Co Limited | Financial services | 2022 |
| Munash Ltd | Health & social care | 2020 |
| Munster Scenery Limited | Information & communication | 2024 |
| Musculoskeletal Radiology Ltd | Health & social care | 2019 |
| Musgrove Maltings Management Company Limited | Households | 2012 |
| Mushonga Motors Ltd | Wholesale & retail | 2025 |
| Muya Research Management Ltd | Professional & scientific | 2019 |
| MV Electrical Engineers Ltd | Construction | 2017 |
| MV Electrical Ltd | Construction | 2022 |
| MV Innovate Limited | Information & communication | 2021 |
| MV Renewables Ltd | Construction | 2022 |
| MVK77 Ltd | Construction | 2016 |