| M & S Tile and Flooring Ltd | Construction | 2023 |
| M & T Burry Ltd | Construction | 2025 |
| M and M Homes London Limited | Real estate | 2019 |
| M Churchouse Consultancy Limited | Other services | 2022 |
| M D Grey Limited | Agriculture & fishing | 2017 |
| M D Home Solutions Limited | Construction | 2015 |
| M D James Ltd | Construction | 2018 |
| M Gullis Limited | Construction | 2010 |
| M H Suspension Limited | Wholesale & retail | 2005 |
| M Hanson Limited | Financial services | 2011 |
| M Huttel Limited | Construction | 2008 |
| M J Bendall and Partners Limited | Agriculture & fishing | 2008 |
| M J Brickwork Contracting Ltd | Construction | 2021 |
| M J Church (Plant) Limited | Water & waste | 1984 |
| M J Church Properties Limited | Real estate | 1997 |
| M L Maslin Limited | Construction | 2016 |
| M O Signalling Limited | Administrative & support | 2013 |
| M P Engineering (Chippenham) Limited | Professional & scientific | 2010 |
| M R E & B a Hawker Limited | Agriculture & fishing | 2009 |
| M R W Engineering Ltd | Administrative & support | 2001 |
| M W Services (Calne) Limited | Wholesale & retail | 2002 |
| M&A Properties (SW) Limited | Real estate | 2026 |
| M&D Equipment Hire Ltd | Administrative & support | 2024 |
| M&M Hairitage Ltd | Real estate | 2024 |
| M&P Handyman Services Ltd | Construction | 2017 |
| M. T. Barnsley Limited | Transport & logistics | 1971 |
| M.A.S.L Corporation Limited | Wholesale & retail | 2007 |
| M.J.B Group Ltd | Administrative & support | 2022 |
| M.R. Vines & SON Limited | Agriculture & fishing | 2007 |
| M.Roberts Holdings Limited | Professional & scientific | 2023 |
| M2 Resin Floors Ltd | Construction | 2025 |
| M4 Escapes Ltd | Arts & recreation | 2020 |
| M4 Karting Ltd | Arts & recreation | 2016 |
| M4 Minimoto Ltd | Wholesale & retail | 2023 |
| M4 Motor Group Ltd | Wholesale & retail | 2024 |
| M4 Tyres (Wiltshire) Ltd | Wholesale & retail | 2021 |
| M9 Limited | Real estate | 1990 |
| MA55 Limited | Real estate | 2023 |
| Mabikacare Limited | Public administration | 2022 |
| MAC Soldering Limited | Information & communication | 2005 |
| Macbean Consulting Limited | Professional & scientific | 2024 |
| Macdonell Ceramics Ltd | Manufacturing | 2002 |
| Mace Systems Limited | Information & communication | 2010 |
| Macuvision Europe Limited | Extraterritorial | 2006 |
| MAD BAD Productions CIC | Arts & recreation | 2024 |
| Madders Hatters Property Limited | Real estate | 2022 |
| Madison Rose Consultancy Ltd | Professional & scientific | 2024 |
| Madison Rose Properties Ltd | Real estate | 2023 |
| Maelor Laboratories Limited | Manufacturing | 1997 |
| Maggs Consulting Ltd | Administrative & support | 2006 |
| Maggs Financial Services Ltd | Financial services | 2022 |
| Magic Cleaning Solutions Limited | Wholesale & retail | 2018 |
| Magiclean Services Ltd | Administrative & support | 2020 |
| Magnet Mouse Ltd | Wholesale & retail | 2013 |
| Maido Ltd | Extraterritorial | 2015 |
| Mainstay (IOW) Ltd | Real estate | 2022 |
| MAK Building Limited | Construction | 2003 |
| Makepeace Building Limited | Construction | 2004 |
| Makery Live Ltd | Education | 2020 |
| Malford Environmental Consulting Ltd | Professional & scientific | 2009 |
| Malford Farm Court Management Ltd | Households | 2021 |
| Mallimania Events Limited | Other services | 2017 |
| Mallu Butchers Ltd | Wholesale & retail | 2025 |
| Malmesbury Curtains and Blinds Ltd | Manufacturing | 2018 |
| Malmesbury Road Garage Limited | Wholesale & retail | 1992 |
| Mamot Properties Ltd | Real estate | 2024 |
| Manana Flatlets Limited | Real estate | 1964 |
| Mander Duffill Financial Advisers Ltd | Professional & scientific | 2023 |
| Mander Duffill Holdings Limited | Financial services | 2024 |
| Mander Duffill Limited | Professional & scientific | 2009 |
| Mando Consortium Limited | Financial services | 2018 |
| Mando Property (Commercial) Investments Limited | Real estate | 2025 |
| Mando Property Investments Limited | Real estate | 2025 |
| Mando Solutions Limited | Administrative & support | 2007 |
| Mane Hair Company Ltd | Other services | 2023 |
| Mannings Joinery Limited | Construction | 2011 |
| Manny's Ices Ltd | Hospitality | 2025 |
| Manor Farm Plant Hire Limited | Agriculture & fishing | 1994 |
| Manor Park Hotel Limited | Hospitality | 2018 |
| Manor Sales Limited | Wholesale & retail | 2008 |
| Maple Farming Ltd | Financial services | 2023 |
| Marble Aerospace Limited | Manufacturing | 2016 |
| Marchez Limited | Information & communication | 2006 |
| Marco Migliari Limited | Administrative & support | 2012 |
| Marcus Anstie Limited | Construction | 2000 |
| Marhew Consulting Limited | Professional & scientific | 2010 |
| Maris Construction Cumbria Ltd | Construction | 2024 |
| Maris Homes (Cumbria) Limited | Construction | 2021 |
| Marisight Ltd | Professional & scientific | 2026 |
| Mark Hutchings Limited | Construction | 2011 |
| Mark J Wood Associates Limited | Professional & scientific | 2011 |
| Mark Paris IT Services Limited | Information & communication | 2018 |
| Mark Power Safeguarding Ltd | Professional & scientific | 2020 |
| Marketing & Travel Limited | Arts & recreation | 2018 |
| Marlin Mechanical Limited | Manufacturing | 2023 |
| Marlinmedia Limited | Professional & scientific | 2018 |
| MARQUE2 Valeting and Detailing Ltd | Administrative & support | 2015 |
| Marshall Bespoke Furniture Ltd | Manufacturing | 2022 |
| Marshfest CIC | Administrative & support | 2026 |
| Marshfield Associates Limited | Administrative & support | 2016 |