| Marshfield Honey Limited | Manufacturing | 2019 |
| Marshfield Motocross Club Limited | Arts & recreation | 2004 |
| Marshfield Network CIC | Information & communication | 2025 |
| Marshfield Traditional Farm Limited | Agriculture & fishing | 2005 |
| Marshwood Financial Services Ltd | Financial services | 2003 |
| Martin Bowler Limited | Administrative & support | 2002 |
| Masons Wharf (Corsham) Management Company Limited | Administrative & support | 2009 |
| Matchdemand Services Limited | Real estate | 1992 |
| Math Abacus for Kids Ltd | Education | 2023 |
| Matinai Ltd | Information & communication | 2019 |
| Matt Perks Ltd | Construction | 2014 |
| Matterhorn Backoffice Solutions Ltd | Administrative & support | 2024 |
| Matthew J Storey Limited | Financial services | 2005 |
| Mattvac Carpet Cleaning Services Ltd | Administrative & support | 2026 |
| MAV Consultancy Services Limited | Professional & scientific | 2018 |
| MAW Media Limited | Arts & recreation | 2011 |
| MAX Baird Ltd | Financial services | 2022 |
| MAY Holdings Limited | Professional & scientific | 2005 |
| Maybridge Properties Limited | Professional & scientific | 1999 |
| Mayfly Care Consultancy Ltd | Professional & scientific | 2021 |
| Mayfly's Reach Limited | Information & communication | 2020 |
| Mayla Consulting Limited | Information & communication | 2024 |
| Maynstay Ltd | Extraterritorial | 2015 |
| Mbbells Limited | Construction | 2018 |
| MBC Restaurants UK Ltd | Hospitality | 2023 |
| Mccabe Law Ltd | Professional & scientific | 2020 |
| Mccall Holdings Ltd | Administrative & support | 2018 |
| MCE Property Limited | Real estate | 2019 |
| MCK Group Limited | Financial services | 2024 |
| MCN Resilience Ltd | Administrative & support | 2024 |
| MD Mackinnon Builder Limited | Construction | 2005 |
| MDG Property Group Ltd | Real estate | 2025 |
| Mdumitru Ltd | Hospitality | 2022 |
| Mead Management Services Limited | Professional & scientific | 1996 |
| Meadows Plumbing and Heating Services Limited | Construction | 2023 |
| Media Sport Limited | Information & communication | 2002 |
| Mediascape Wiltshire Ltd | Information & communication | 2025 |
| Medisurge International Limited | Manufacturing | 2026 |
| Meditec Training Ltd | Professional & scientific | 2010 |
| Mediterranean Restaurant U.K Ltd | Hospitality | 2025 |
| Medlar Consultancy Limited | Agriculture & fishing | 2021 |
| Medullary RAY Designs Ltd | Construction | 2021 |
| Meehan Properties Ltd | Real estate | 2026 |
| MEG and MOG Limited | Information & communication | 2014 |
| Melksham Recycling & Skips Ltd | Water & waste | 2023 |
| Melksham Tyre Supplies Ltd | Wholesale & retail | 2019 |
| Melksham Uniform Exchange C.I.C. | Other services | 2024 |
| Mellbreak Consultancy Limited | Professional & scientific | 2021 |
| Mellor Roofing Limited | Construction | 2019 |
| Melora Consultancy Limited | Professional & scientific | 2021 |
| Melt Productions Ltd. | Arts & recreation | 2015 |
| Melton Concrete Holdings Ltd | Financial services | 2024 |
| Melton Concrete Products Ltd | Wholesale & retail | 2020 |
| Mendip Hospital Cemetery | Arts & recreation | 2001 |
| Meolc Consultants Ltd | Education | 2015 |
| Mercers Autocraft Ltd | Wholesale & retail | 2026 |
| Merlin Automotive Group Limited | Wholesale & retail | 2026 |
| Merlin Mail Order Limited | Wholesale & retail | 1985 |
| MES Consulting Services Ltd | Professional & scientific | 2019 |
| Metabox Limited | Information & communication | 2015 |
| Metagame.Services Limited | Information & communication | 2020 |
| Metal Installations Ltd | Manufacturing | 2026 |
| Metcalfe Rail Safety Limited | Administrative & support | 2017 |
| Methuen Property Ltd | Real estate | 2022 |
| Metpro Hammermill Limited | Professional & scientific | 1988 |
| Metre Squared Properties Ltd | Real estate | 2024 |
| Metre Squared Services Ltd | Construction | 2018 |
| Metrotile (U.K.) Limited | Transport & logistics | 1992 |
| Meyrick-Jones LLP | | 2024 |
| MGI 720 Ltd | Financial services | 2018 |
| MGI Coutier Finance Limited | Manufacturing | 2012 |
| MH Transport South West Limited | Transport & logistics | 2025 |
| MHR Webber & Co Ltd | Real estate | 2023 |
| MI Trades Property Services Limited | Construction | 2024 |
| Miah Catering Ltd | Hospitality | 2022 |
| Michael Antony Lettings Limited | Real estate | 2012 |
| Michael Antony Ltd | Real estate | 1987 |
| Michael Bell Farrier Limited | Administrative & support | 2003 |
| Michael EDEN777 Ltd | Manufacturing | 2001 |
| Michael Grange Limited | Agriculture & fishing | 2011 |
| Michael Napier Guiding Limited | Administrative & support | 2025 |
| Michael Pillinger Ltd | Other services | 2022 |
| Michael R Collier Ltd | Transport & logistics | 2014 |
| Mick Sparks Limited | Construction | 2014 |
| Microft Solutions Ltd | Administrative & support | 2019 |
| Midas Communications Limited | Information & communication | 2015 |
| Middledale Foods Limited | Wholesale & retail | 1996 |
| Midgell Court Farm Ltd | Agriculture & fishing | 2022 |
| Midnight Fade Ltd | Information & communication | 2015 |
| Midsomer Veterinary Centre Limited | Professional & scientific | 2014 |
| Mike Matthews Construction Ltd | Construction | 2019 |
| Mike Wood Motor Works Ltd | Wholesale & retail | 2017 |
| Mike Wood Tyres Limited | Wholesale & retail | 2005 |
| Miles Byron (Village & Country Homes) Ltd. | Real estate | 2025 |
| Milk & Tweed Limited | Wholesale & retail | 2015 |
| Milk & Tweed Studio Limited | Information & communication | 2002 |
| Millbeck Forests Limited | Agriculture & fishing | 2014 |
| Milleva Limited | Administrative & support | 2014 |
| Millicent Capital UK Limited | Professional & scientific | 2023 |
| Millicent Star Limited | Professional & scientific | 2020 |