| MBM (SW) Limited | Wholesale & retail | 2020 |
| Mboxes UK Ltd | Manufacturing | 2020 |
| MC Building Solutions SW Ltd | Construction | 2026 |
| MC FX Ltd | Real estate | 2022 |
| Mccloud Remedy Limited | Other services | 2022 |
| Mcconnell & ROE Medicolegal Services Ltd | Information & communication | 2026 |
| Mcconney-Allen Civil Engineering Consultancy Ltd | Construction | 2007 |
| Mccool Property Maintenance Ltd | Real estate | 2019 |
| Mccormick Motor Care Ltd | Wholesale & retail | 2024 |
| MCE SW Ltd | Construction | 2016 |
| MCH Accident Repair Centre Ltd | Wholesale & retail | 2025 |
| MCH Works Ltd | Information & communication | 2025 |
| Mckinley Consultancy Ltd | Professional & scientific | 2019 |
| Mckinley Properties SW Limited | Construction | 2025 |
| Mclaren Design Services Ltd | Professional & scientific | 2021 |
| Mcmanus Commercial Nurseries Limited | Administrative & support | 2017 |
| Mcnabb Composites Ltd | Construction | 2026 |
| Mcnoughts & Crosses Ltd | Hospitality | 2018 |
| Mcscience CIC | Education | 2024 |
| Mcsheen Solutions Ltd | Professional & scientific | 2011 |
| MCT Property SW Ltd | Real estate | 2025 |
| MD Investment Property and Letting Limited | Real estate | 2023 |
| MD PUB Services Limited | Hospitality | 2021 |
| MD Victory Ltd | Wholesale & retail | 2024 |
| Md&Go Limited | Transport & logistics | 2021 |
| MDC Middle East Ltd | Information & communication | 2014 |
| Mdcg Ltd | Professional & scientific | 2012 |
| MDH Medical Services Ltd | Health & social care | 2024 |
| Mdkm Limited | Health & social care | 2026 |
| Mdnr Property Ltd | Real estate | 2020 |
| MDO Project Management Ltd | Construction | 2020 |
| MDP Electrical SW Ltd | Construction | 2018 |
| MDV Events Ltd | Arts & recreation | 2023 |
| Mead Marine Ltd | Professional & scientific | 2025 |
| Meade Construct Ltd | Administrative & support | 2016 |
| Meadowfoot Management Company Ltd | Households | 2021 |
| Meat Trade Link SW Ltd | Professional & scientific | 2021 |
| Mecal Limited | Other services | 1993 |
| Mechanical Services SW Limited | Construction | 2023 |
| Mechanical Site Services Ltd | Construction | 2015 |
| Mechanus Gravitas Ltd | Construction | 2025 |
| Mechz Robotics Ltd | Professional & scientific | 2024 |
| Medfield Southwest Limited | Other services | 2010 |
| Medi Derma Limited | Other services | 2024 |
| Media Infinity Limited | Manufacturing | 2022 |
| Media Jelly Limited | Manufacturing | 2014 |
| Mediation Cardiff Limited | Professional & scientific | 2014 |
| Medical Clerical Bureau Limited | Administrative & support | 2004 |
| Medical Professional Limited | Financial services | 2013 |
| Medicell Batteries Ltd | Wholesale & retail | 2010 |
| Medico Aesthetics Limited | Health & social care | 2017 |
| Medico Care Limited | Administrative & support | 2020 |
| Medico Healthcare Services Ltd | Health & social care | 2023 |
| Medics on the Move (Plymouth) Limited | Real estate | 2006 |
| Medics on the Move South West Ltd | Real estate | 2022 |
| Medipod Care Technologies Ltd | Information & communication | 2026 |
| Medix Investments Ltd | Real estate | 2025 |
| Medix-Care UK Ltd | Information & communication | 2021 |
| Medq Limited | Health & social care | 2015 |
| Medrawy Ltd | Health & social care | 2025 |
| Meds Kitchen Limited | Hospitality | 2021 |
| Medtech Consulting Solutions Ltd | Health & social care | 2025 |
| MEG Competitions Ltd | Administrative & support | 2026 |
| Mega - Make Earth Great Again Limited | Education | 2022 |
| Mega Justice CIC | Public administration | 2024 |
| Megashouts Ltd | Information & communication | 2014 |
| Mehdi Property Limited | Other services | 2024 |
| Meira in Style Ltd | Wholesale & retail | 2024 |
| Melanie Walker Consulting Ltd | Professional & scientific | 2024 |
| Melba Matrix Ltd | Administrative & support | 2010 |
| Mellowlegal Ltd | Professional & scientific | 2021 |
| Membland Court Owners Limited | Households | 2022 |
| Memory Matters CIC | Education | 2010 |
| Memory Matters Technology Ltd | Information & communication | 2025 |
| Mendip Control Systems Ltd. | Professional & scientific | 2004 |
| Menopause Decisions Ltd | Health & social care | 2022 |
| Mental Engineering Ltd | Arts & recreation | 2024 |
| Mental Health Support Training and Consultancy Ltd | Education | 2006 |
| MEP Engineering Ltd | Professional & scientific | 2019 |
| MEP Systems Limited | Construction | 2016 |
| Mercare (SW) Ltd | Wholesale & retail | 2019 |
| Mercury Construction (South West) Limited | Construction | 2006 |
| Meridian Fitout Ltd | Construction | 2026 |
| Meridian Investment Group Limited | Hospitality | 2024 |
| Meridian Sea Limited | Wholesale & retail | 2003 |
| Merit Foods Hub CIC | Hospitality | 2025 |
| Merren Carpentry & Construction Limited | Construction | 2025 |
| Merri Building Services Limited | Construction | 2023 |
| Merri Developments (Gweek) Limited | Construction | 2023 |
| Merri Holdings Limited | Financial services | 2023 |
| Merseycomms Limited | Information & communication | 2017 |
| Mersirl Ltd | Wholesale & retail | 2025 |
| Mesguen (UK) Limited | Transport & logistics | 1975 |
| Messi 10 Ltd | Hospitality | 2026 |
| MET House Limited | Households | 2022 |
| MET Properties 25 Ltd | Real estate | 2021 |
| Metal Craft SW Ltd | Manufacturing | 2023 |
| Metal Solutions (SW) Limited | Professional & scientific | 2002 |
| Metcaf Ltd | Professional & scientific | 2021 |
| Metempsychosis Limited | Real estate | 2023 |