| M J Self Limited | Wholesale & retail | 2015 |
| M L Williams Drylining Limited | Construction | 2026 |
| M&J Delights Limited | Wholesale & retail | 2025 |
| M.A.C. Properties (SW) Ltd | Real estate | 2021 |
| M.A.T Consulting Services Ltd | Financial services | 2015 |
| M.A.X. Haulage & Plant Ltd | Transport & logistics | 2022 |
| M.J.H. Export Limited | Wholesale & retail | 1983 |
| M.Wyatt Construction Ltd | Construction | 2019 |
| M2 Civil and Structural Limited | Professional & scientific | 2020 |
| MAB Southern Limited | Real estate | 1998 |
| MAC Stone Limited | Wholesale & retail | 2014 |
| Maceeam Limited | Manufacturing | 2018 |
| Mactown Developments Ltd | Construction | 2022 |
| Maddern Developments Ltd | Construction | 2024 |
| Magdalen and Cross Ltd | Construction | 2007 |
| Mainco Construction Limited | Construction | 2025 |
| Mamidet Limited | Wholesale & retail | 2025 |
| Manor Road Fish Bar Ltd | Hospitality | 2024 |
| Manta Global Ltd | Information & communication | 2025 |
| Manton Close Limited | Professional & scientific | 2005 |
| Maple (186) Limited | Real estate | 2003 |
| Maple 1959 Limited | Extraterritorial | 2015 |
| Marcato Limited | Information & communication | 2016 |
| Marcella Property Limited | Real estate | 2021 |
| Maria@Lyons Ltd | Administrative & support | 2018 |
| Mark Ellerby Architects Limited | Professional & scientific | 2018 |
| Mark Norris Electrical Limited | Construction | 2013 |
| Market Fabrics Ltd | Wholesale & retail | 2011 |
| Markhams Windscreens Ltd | Wholesale & retail | 2010 |
| Marks Cars Ltd | Other services | 2016 |
| Marshall Family Logistics Limited | Transport & logistics | 2019 |
| Martial Arts Leisure (UK) Ltd. | Arts & recreation | 2003 |
| Marybee Limited | Professional & scientific | 1987 |
| Masterops Technologies Ltd | Information & communication | 2026 |
| Mathematics in Education and Industry | Education | 1996 |
| Mattech Motor Company Ltd | Wholesale & retail | 2019 |
| Matthew Samuel Properties Ltd | Construction | 2022 |
| Matty's Street Food Ltd | Hospitality | 2025 |
| Mauveflow Limited | Other services | 2022 |
| Mave Removals Ltd | Other services | 2021 |
| Maya Design and Build Ltd | Construction | 2021 |
| Maylands Farm Limited | Agriculture & fishing | 2025 |
| MBA Engineering Ltd | Manufacturing | 2015 |
| Mcclean Cleaning Company Limited | Administrative & support | 2022 |
| Mcclurg Plumbing & Heating Ltd | Construction | 2017 |
| MCE Systems Limited | Information & communication | 1999 |
| Mcgill Warmley Limited | Real estate | 2005 |
| Mckerracher Digital Ltd | Information & communication | 2017 |
| Mdbit Limited | Information & communication | 2008 |
| Meadowbrook (Wiltshire) CIC | Other services | 2021 |
| Meadowlands (Staverton) RTM Company Ltd | Households | 2025 |
| Meadowlands (Trowbridge) Management Company Limited | Households | 2006 |
| Mecentra Ltd | Wholesale & retail | 2025 |
| Media Bomb Limited | Administrative & support | 2015 |
| Mediakinetic Limited | Information & communication | 2009 |
| Mega Capture Limited | Arts & recreation | 2025 |
| Mega Taxi Ltd | Transport & logistics | 2025 |
| Meiyume (UK) Limited | Manufacturing | 1950 |
| Meiyume Holdings (UK) Limited | Professional & scientific | 2019 |
| Meiyume Retail Solutions (UK) Limited | Wholesale & retail | 2009 |
| Meka Solutions Ltd | Wholesale & retail | 2025 |
| Melekfood Limited | Hospitality | 2024 |
| Melksham Court Management Limited | Households | 1992 |
| Melksham Limousines Limited | Administrative & support | 2001 |
| Melksham Town Football Club Ltd | Arts & recreation | 2010 |
| MEN and Mountains Ltd | Arts & recreation | 2026 |
| Metal Products (Warminster) Ltd | Manufacturing | 1996 |
| Metal Trade Comax (UK) Limited | Construction | 2016 |
| Metatutor Ltd | Education | 2017 |
| Metis Tax Limited | Professional & scientific | 2023 |
| Metis Wealth Planning Limited | Professional & scientific | 2025 |
| MG Adams Plumbing & Heating Limited | Construction | 2008 |
| MGT Care Solutions Ltd | Health & social care | 2018 |
| Microdigit Systems Ltd | Information & communication | 2023 |
| Middleton Palmer Ltd | Real estate | 2024 |
| Mike Brickell Carpentry Limited | Manufacturing | 2025 |
| Miles Mantay Electrical Ltd | Construction | 2020 |
| Milk Supply Solutions Ltd | Professional & scientific | 2018 |
| Miller Digital Limited | Professional & scientific | 2023 |
| Millies Mutts Ltd | Wholesale & retail | 2023 |
| Millmead Motors Limited | Professional & scientific | 1961 |
| Milly Molly Mandy's Domestic Services Limited | Administrative & support | 2021 |
| MIMIBAABA2 Ltd | Health & social care | 2021 |
| Mindscape Property Services Ltd | Real estate | 2023 |
| Minerva Publications Limited | Information & communication | 2011 |
| Mini Market Express Ltd | Wholesale & retail | 2024 |
| Minimelt Glass Ltd | Extraterritorial | 2012 |
| Mirelle Limited | Wholesale & retail | 2012 |
| Mission Forecast Ltd | Financial services | 2018 |
| Mistfix Point Ltd | Information & communication | 2025 |
| MJ Coleman Ltd | Health & social care | 2010 |
| Mjls W&L Ltd | Construction | 2011 |
| MK Energy Consulting Ltd | Professional & scientific | 2019 |
| MK Polestar Catering Ltd | Hospitality | 2024 |
| MK Solutions (SW) Ltd | Construction | 2014 |
| MM Groundworks & Civils Ltd | Construction | 2025 |
| Mmxxv Ltd | Other services | 2018 |
| MNH Management Limited | Administrative & support | 2020 |
| Mogeng Ltd | Professional & scientific | 2025 |
| Mogul Tandoori Indian Cuisine Limited | Hospitality | 2021 |