| M. J. Farrington Limited | Manufacturing | 1997 |
| M. Knights Electrical Ltd. | Construction | 2018 |
| M. Miah Ltd | Professional & scientific | 2015 |
| M. T. Cole & SON Limited | Construction | 2003 |
| M.A.B. Environmental Limited | Manufacturing | 2022 |
| M.A.F.H.S. Ltd | Health & social care | 2013 |
| M.A.G.L. Ltd | Mining & quarrying | 2026 |
| M.A.P. Properties LLP | | 2009 |
| M.B. (Hants) Ltd | Wholesale & retail | 1979 |
| M.C&M. Construct Ltd | Construction | 2020 |
| M.C. Hall Limited | Construction | 2007 |
| M.C.R.A. Ltd | Households | 2002 |
| M.C.S. Consultancy Limited | Construction | 1998 |
| M.D.T. (Southern) Ltd | Administrative & support | 2003 |
| M.D.T. Properties Limited | Financial services | 2012 |
| M.F.C. Electrical Limited | Construction | 1999 |
| M.G.S. Building & Electrical Contractors Limited | Construction | 1988 |
| M.H.Parmar Ltd | Real estate | 2025 |
| M.J. Computer Services Limited | Professional & scientific | 1982 |
| M.J.I. Farming Limited | Agriculture & fishing | 1995 |
| M.King Roofing & Cladding Ltd | Construction | 2010 |
| M.Lcareservices Limited | Health & social care | 2025 |
| M.O. Buckland & SON Ltd | Construction | 2018 |
| M.O.T.'s @ Tom's Limited | Wholesale & retail | 2005 |
| M.R. Anstis Ltd | Construction | 2007 |
| M.S. Randhawa Holdings Ltd | Financial services | 2024 |
| M1VISUALPRODUCTION Ltd | Information & communication | 2025 |
| M27 Home Improvements Ltd | Construction | 2025 |
| M2L Training and Consultancy Ltd | Other services | 2017 |
| M2M Contractor Limited | Construction | 2010 |
| M3 Marketing (Southern) Ltd | Wholesale & retail | 2021 |
| M4 I Properties Ltd | Real estate | 2024 |
| M74 Post Ltd | Information & communication | 2022 |
| MA KO & JO KO Ltd | Transport & logistics | 2014 |
| MA South Commercial Ltd | Real estate | 2026 |
| MA South Properties Ltd | Real estate | 2020 |
| Ma&Cla Limited | Transport & logistics | 2020 |
| MAA Logistics & Courier Limited | Transport & logistics | 2025 |
| MAA Trading (Southern) Limited | Construction | 2005 |
| Maalu Ceylon Limited | Hospitality | 2025 |
| Maami Grocery and Supply Ltd | Wholesale & retail | 2024 |
| MABEL9 Property Ltd | Construction | 2024 |
| Mabood Estates Limited | Real estate | 2023 |
| MAC (SPV) Limited | Real estate | 2020 |
| MAC Access Ltd | Construction | 2021 |
| MAC Hair (Chandlers Ford) Limited | Other services | 2013 |
| MAC Marine Ltd | Professional & scientific | 2023 |
| Macarthur Consulting Limited | Information & communication | 2025 |
| Macbtc Limited | Administrative & support | 2022 |
| Macca Media Limited | Information & communication | 2011 |
| Macdonald Dennis Holdings Ltd | Financial services | 2018 |
| Macdonald Family Finance Company Limited | Financial services | 2018 |
| Macey Enterprises Ltd | Construction | 2020 |
| Macfarlane Business Advice Ltd | Professional & scientific | 2025 |
| Macfield Properties Ltd | Real estate | 2020 |
| Macfyld Group Limited | Other services | 2019 |
| Macgillivray Engineering Ltd | Construction | 2012 |
| Mach 1 Spoof Ltd | Hospitality | 2012 |
| Mach Cargo Ltd | Construction | 2016 |
| Mach One Management Limited | Financial services | 2016 |
| Machazcare Limited | Transport & logistics | 2015 |
| MACHIC4 Limited | Health & social care | 2021 |
| Machine Safety UK Ltd | Manufacturing | 2025 |
| Macindoe Solutions Ltd | Construction | 2019 |
| Macisaac Financial Planning Limited | Professional & scientific | 2020 |
| Mackavan Holdings LLP | | 2013 |
| Mackavan Holdings Two LLP | | 2019 |
| Maclean Medical Services Limited | Health & social care | 2013 |
| Macnab Holdings Limited | Financial services | 2020 |
| Macro Developments (Portsmouth) Limited | Manufacturing | 1978 |
| Macrogate Limited | Administrative & support | 1982 |
| Macrophox Ltd | Professional & scientific | 2018 |
| Macrow Building Services Limited | Construction | 2022 |
| Macsprays Ltd | Construction | 2025 |
| Macytsu Ltd. | Health & social care | 2010 |
| MAD About Money Limited | Professional & scientific | 2022 |
| MAD Hatter Hats Boutique Limited | Wholesale & retail | 2021 |
| MAD Monkey Mechanical Ltd | Wholesale & retail | 2020 |
| MAD4CARS.COM Limited | Professional & scientific | 2013 |
| Madaca Transport Limited | Transport & logistics | 2025 |
| Madalin Trans Ltd | Transport & logistics | 2024 |
| Madalina Safterie Ltd | Health & social care | 2015 |
| Madax Ltd | Transport & logistics | 2020 |
| Madden Driveways & Surfacing Ltd | Construction | 2026 |
| Maddison Street Management Company Limited | Households | 1987 |
| Maddocks Plumbing & Heating Ltd | Construction | 2019 |
| Made 2 Measure (Holdings) Limited | Financial services | 2011 |
| Made 2 Measure Bespoke Furniture (Southampton) Ltd | Manufacturing | 2018 |
| Made by Fuse Ltd | Information & communication | 2007 |
| Made Construction Limited | Construction | 2008 |
| Made in Here Limited | Wholesale & retail | 2018 |
| Made in M. E. G Limited | Professional & scientific | 2007 |
| Made With Love Hope and Joy Ltd | Hospitality | 2015 |
| Madebytrouble Ltd | Wholesale & retail | 2022 |
| Madeena London Limited | Wholesale & retail | 2020 |
| Madesmile Ltd | Health & social care | 2024 |
| Madinah Properties Limited | Real estate | 2003 |
| Madness Coffee Ltd | Wholesale & retail | 2026 |
| Madom & Menshira Limited | Manufacturing | 2024 |
| Madrisa Court Management Company Limited | Households | 1975 |