| Marquise Alloys Ltd | Wholesale & retail | 2016 |
| Marsette Ltd | Real estate | 2026 |
| Marshall Arbitration Services Ltd | Professional & scientific | 2013 |
| Marshall Estate Agents Ltd | Real estate | 2024 |
| Marshall Tail Lift Ltd | Manufacturing | 1977 |
| Marshalls Tisbury Ltd | Construction | 2009 |
| Marshisaacs Ltd | Construction | 2018 |
| Martin Grain Company Limited | Real estate | 1982 |
| Martin Quigley Limited | Construction | 1997 |
| Martin's Constructions Ltd | Construction | 2013 |
| Martinique Property Limited | Administrative & support | 2002 |
| Martins Rise Management Limited | Households | 1999 |
| Martyn Simpson Studio Furniture Ltd | Manufacturing | 2024 |
| Marvel Design & Build Ltd | Construction | 2019 |
| Marvin Sundays Limited | Wholesale & retail | 2021 |
| Maschler Properties Limited | Real estate | 2016 |
| Maschler Pubs Limited | Hospitality | 2016 |
| Master Land and Planning Limited | Professional & scientific | 2021 |
| Master of Rain Media Ltd | Other services | 2015 |
| Master Planning Limited | Extraterritorial | 2021 |
| Master Planning Services Limited | Extraterritorial | 2021 |
| Master Real Estate Holdings Ltd | Financial services | 2021 |
| Masters Sport UK Limited | Arts & recreation | 2016 |
| Mata Construction Limited | Construction | 2009 |
| Material Facts Limited | Administrative & support | 2014 |
| Mathshop Limited | Information & communication | 2001 |
| Maton Limited | Financial services | 2015 |
| Maton Tax Accounting Limited | Professional & scientific | 2015 |
| Matt Prime Songs Ltd | Information & communication | 2007 |
| Matterhorn Limited | Wholesale & retail | 2012 |
| Matthew Burt Limited | Manufacturing | 2011 |
| Matthew Feltham Ltd | Administrative & support | 2003 |
| Matthew Hallett Ltd. | Real estate | 2014 |
| Matthew Wakefield EYE Surgery Limited | Health & social care | 2018 |
| Matthews Flower Growers Company Ltd | Agriculture & fishing | 2014 |
| Mauls Wine and Cheese Bar Ltd | Wholesale & retail | 2017 |
| Maurice Flower & SON Limited | Agriculture & fishing | 1958 |
| Maven Accounting and Bookkeeping Limited | Professional & scientific | 2018 |
| Mavennest Ltd | Administrative & support | 2026 |
| Max's Sandwich Shop Limited | Hospitality | 2015 |
| Maxi Taxi Travel Solutions Ltd | Transport & logistics | 2026 |
| Maximus International Operations Ltd | Administrative & support | 2014 |
| Maxted Close Management Company Limited | Households | 2008 |
| Maxwell Research Limited | Professional & scientific | 2010 |
| Mayes Investment Group Ltd | Information & communication | 2026 |
| Mayfly Farms Limited | Administrative & support | 2016 |
| Maywood Stud Ltd | Agriculture & fishing | 2026 |
| MBC (Stirling) Limited | Real estate | 2018 |
| MBC Carpentry Ltd | Construction | 2020 |
| MBI S.A Hevea NO.1 Limited Partnership | | 2011 |
| MC Horizons Limited | Information & communication | 2024 |
| MC7 Ltd | Health & social care | 2022 |
| Mccarthy Inter Africa Ltd | Wholesale & retail | 2013 |
| Mccrimmon & Reid Limited | Hospitality | 2014 |
| MCD Construction (Wilts) Limited | Construction | 2015 |
| Mceniry & Cooley Building Services Ltd | Construction | 2019 |
| Mceniry Building Services Ltd | Construction | 2025 |
| Mcgregor Property Services Limited | Construction | 2013 |
| Mckeown & Co. LLP | | 2015 |
| Mckinley Residential Limited | Real estate | 2011 |
| Mckj Ltd | Professional & scientific | 2016 |
| Mclaren Medicals Ltd | Health & social care | 2011 |
| Mcloughlin Enterprises Limited | Professional & scientific | 2012 |
| MCM Estates Limited | Real estate | 2016 |
| MCP Vehicle Services Ltd | Wholesale & retail | 2023 |
| Mcwilliams Property Investments Limited | Real estate | 2025 |
| MD Farming Limited | Agriculture & fishing | 2013 |
| MD Roofing Ltd | Construction | 2022 |
| MD Salisbury Ltd | Professional & scientific | 2018 |
| MDH Makel Holding Ltd | Financial services | 2024 |
| MDO Design Limited | Professional & scientific | 2008 |
| Mdrlw Ltd | Arts & recreation | 2024 |
| Meacham's Car Centre Westbury Limited | Wholesale & retail | 2025 |
| Meadow Brook (Sandymoor) Management Company Limited | Households | 2025 |
| Meadow Keep Limited | Extraterritorial | 2013 |
| Meant 2 Rent Group Ltd | Real estate | 2025 |
| Measured Engineering Surveys Ltd | Construction | 2019 |
| Mecpram Auto Ltd | Transport & logistics | 2022 |
| Media Junk Limited | Information & communication | 2015 |
| Media Recall Limited | Arts & recreation | 2006 |
| Medical Manufacturers Europe Limited | Wholesale & retail | 2013 |
| Medico Management Limited | Administrative & support | 2011 |
| Medisain Ltd | Health & social care | 2019 |
| Mediseco Limited | Administrative & support | 2022 |
| Mediserve Private Ltd | Health & social care | 2012 |
| Medway Road Depot Management Company Limited | Households | 2009 |
| MEE 2 Construction Ltd | Construction | 2008 |
| Meenj Limited | Health & social care | 2023 |
| Meercat Construction Ltd | Construction | 2022 |
| Meet the Muckers (Dorset) Ltd | Wholesale & retail | 2020 |
| Mehmood Equities (UK) Limited | Financial services | 2014 |
| Mehmood Properties (UK) Limited | Real estate | 2014 |
| Mehta Respiratory Limited | Health & social care | 2019 |
| Melanthe Florist Ltd | Wholesale & retail | 2026 |
| Melbury Bespoke Interiors Ltd | Manufacturing | 2025 |
| Melbury Developments (South West) Ltd | Construction | 2015 |
| Melbury Greenstone Limited | Manufacturing | 2001 |
| Meldan Limited | Professional & scientific | 2014 |
| Meldiaz Limited | Health & social care | 2023 |
| Melin Newydd Management Company Limited | Households | 2023 |