| MCB Private Ltd | Extraterritorial | 2025 |
| Mccormick & SON Limited | Health & social care | 2011 |
| Mccountants Limited | Professional & scientific | 2010 |
| Mcgregor Consulting Ltd | Professional & scientific | 2015 |
| Mchv Limited | Wholesale & retail | 2008 |
| Mcmurtry Automotive Limited | Professional & scientific | 2016 |
| Mcmurtry Group Limited | Financial services | 2025 |
| MCS Consulting (Associates) Limited | Professional & scientific | 2009 |
| MCS Laundry LLP | | 2020 |
| MDH Health Ltd | Financial services | 2023 |
| MDR Legal Services Limited | Professional & scientific | 2024 |
| Meadows Capital Management LLP | | 2013 |
| Meadows Mcdonald Management Ltd | Financial services | 2005 |
| Measurematch Ltd | Information & communication | 2016 |
| Mechanic Industries Ltd | Professional & scientific | 2011 |
| Medc Consulting Engineers LLP | | 2024 |
| Medicorum Holdings Limited | Financial services | 2024 |
| Medicorum Limited | Professional & scientific | 2010 |
| Medivise Limited | Health & social care | 2017 |
| Medlycott Trustees (NO 1) Limited | Extraterritorial | 2011 |
| Medlycott Trustees (NO 2) Limited | Extraterritorial | 2024 |
| Medscope Medical Supplies Limited | Wholesale & retail | 2022 |
| Megacom Technologies Limited | Information & communication | 1998 |
| Melbury Heights LLP | | 2010 |
| Mellstock Properties Ltd | Real estate | 2023 |
| Mellulah Retreats Limited | Administrative & support | 2024 |
| Membury Limited | Administrative & support | 2007 |
| Memorable Escapes Ltd | Hospitality | 2018 |
| Memorable Holdings Ltd | Financial services | 2018 |
| Menlo Consulting Limited | Administrative & support | 2015 |
| Meraki Poundbury Limited | Other services | 2019 |
| Meram BBQ Kitchen Ltd | Hospitality | 2026 |
| Merley House Events Limited | Households | 2011 |
| Merlin Neuroresearch G Ltd. | Health & social care | 1997 |
| Messrs a & C Wakely & Sons LLP | | 2020 |
| Metal Maritime Limited | Manufacturing | 2026 |
| Metaphor HR Ltd | Professional & scientific | 2025 |
| Metcalfe House Limited | Hospitality | 2018 |
| Metis Holdings Limited | Financial services | 2021 |
| Metropolitan Land Dorset Co Ltd | Administrative & support | 2012 |
| Mews Management (Dorchester) Limited | Households | 1984 |
| Meyers Estate Agents Limited | Real estate | 2011 |
| Meyers Estates Wareham Ltd | Real estate | 2015 |
| Meyers Lettings Limited | Real estate | 2012 |
| Mfpes Limited | Professional & scientific | 2014 |
| MH Business Solutions Limited | Professional & scientific | 2020 |
| MHC (Services) Limited | Professional & scientific | 2001 |
| MHH Business Consultancy Ltd | Professional & scientific | 2025 |
| Mhhjo | Administrative & support | 2021 |
| MI Conversions Ltd | Wholesale & retail | 2022 |
| Mibet Property Maintenance Limited | Construction | 2019 |
| Michael Case Project Engineering Limited | Administrative & support | 2014 |
| Michael D Graham Ltd | Real estate | 2001 |
| Michael's Garden Offices Ltd | Construction | 2026 |
| Michelle Rafferty Limited | Health & social care | 2016 |
| Micky's Flowers Limited | Wholesale & retail | 2021 |
| Micky's Flowers Pokesdown Ltd | Wholesale & retail | 2026 |
| Micro-Network Technology Limited | Professional & scientific | 1998 |
| Microset Products Limited | Wholesale & retail | 1996 |
| MID Dorset Primary Healthcare Limited | Health & social care | 2015 |
| Midnightthirty Ltd | Hospitality | 2023 |
| Midsummer Marriage Ltd | Financial services | 2017 |
| Mike's Motor Services Dorchester Ltd | Wholesale & retail | 2013 |
| Mikintosh Limited | Wholesale & retail | 2014 |
| Milcun Ltd. | Hospitality | 2021 |
| Milton Abbas Maltings Limited | Households | 1985 |
| Milton Court Properties Limited | Households | 2005 |
| Mina's Deli Ltd | Hospitality | 2025 |
| Mineral and Resource Planning Associates Ltd | Professional & scientific | 2002 |
| Minigrid Limited | Construction | 2024 |
| Mintern Fencing and Sheds Ltd | Construction | 2014 |
| Mintern Roofing Ltd | Construction | 2017 |
| Miracle Software Systems UK Limited | Information & communication | 2004 |
| Miriderma Ltd | Health & social care | 2020 |
| Miss Diamond UK Limited | Arts & recreation | 2016 |
| Mister Mattress Ltd | Wholesale & retail | 2024 |
| MIX Music Limited | Information & communication | 1986 |
| MJ Goddard Limited | Professional & scientific | 2011 |
| MJ Kitchens Limited | Construction | 2016 |
| MJC Plumbing & Heating Services Ltd | Construction | 2016 |
| Mje-Tech Ltd | Information & communication | 2024 |
| MJS Plumbing & Heating Limited | Construction | 2012 |
| Mkor Limited | Administrative & support | 2025 |
| Mldp Property Ltd | Real estate | 2023 |
| MN Walker Scaffolding Services Ltd | Construction | 2026 |
| MNG Rentals Ltd | Real estate | 2023 |
| MNS Medical Ltd | Health & social care | 2021 |
| Moana Limited | Wholesale & retail | 2002 |
| Mobile Galaxy Ltd | Wholesale & retail | 2022 |
| Mocean Limited | Manufacturing | 2003 |
| Molten Keys Ltd | Information & communication | 2017 |
| Momo Global Ltd | Professional & scientific | 2016 |
| Momotaro Limited | Professional & scientific | 2020 |
| Monkey Movers Ltd | Administrative & support | 2006 |
| Monkey Puzzle Music Limited | Wholesale & retail | 2019 |
| Monmouth Road (Dorchester) Management Company Limited | Construction | 2000 |
| Montahue Financial Services Ltd | Financial services | 2020 |
| Monterey Place Management Company Ltd | Households | 2023 |
| Montes and Clark Limited | Wholesale & retail | 2015 |
| Montfort Manco Limited | Households | 2026 |