| M. Read Electrical Ltd | Construction | 2014 |
| M.J. Tyrrell Marine Plumbing & Heating Engineer Limited | Manufacturing | 2017 |
| M.R. Timby Electrical Services Ltd | Construction | 2015 |
| M.S Brett Property Limited | Households | 2026 |
| M.W.E. Limited | Construction | 1998 |
| M3 Couriers Limited | Transport & logistics | 2015 |
| M3 Trade Park Management Limited | Real estate | 2006 |
| M4 B&D Limited | Construction | 2011 |
| M4 I Limited | Real estate | 2011 |
| M4 M&C Limited | Professional & scientific | 2011 |
| MA Group Holdings Limited | Financial services | 2024 |
| MAB Wessex Limited | Professional & scientific | 2019 |
| Mabel & MOO Ltd | Wholesale & retail | 2024 |
| MAC Brickwork Limited | Construction | 2023 |
| Macey Macleod Holdings Limited | Financial services | 2016 |
| Machq Ltd | Professional & scientific | 2023 |
| Mackenzie Fit Limited | Administrative & support | 2024 |
| Mackoy SW Ltd | Construction | 2026 |
| Maclehose Associates Ltd | Wholesale & retail | 2013 |
| Macley Homes Limited | Construction | 2025 |
| Macmanus Limited | Administrative & support | 2013 |
| Macmills Ltd | Construction | 2018 |
| Macra GBR Limited | Real estate | 2025 |
| Macra Holdings Ltd | Financial services | 2019 |
| MAD Ventura Ltd | Real estate | 2022 |
| Maddox Property Management Limited | Households | 2023 |
| Maddox Property Sourcing Limited | Real estate | 2024 |
| Made in Europe Ltd | Wholesale & retail | 2025 |
| Madina Food Centre Ltd | Wholesale & retail | 2026 |
| Madini Moyoni Ltd | Professional & scientific | 2023 |
| Madini Moyoni Ventures Ltd | Professional & scientific | 2024 |
| Mads Property Group Ltd | Construction | 2016 |
| Maestro Care Ltd | Health & social care | 2007 |
| Magda DRS Limited | Transport & logistics | 2018 |
| Magic Strand International Limited | Professional & scientific | 2024 |
| Magic Strand Limited | Administrative & support | 2018 |
| Magical New Beginnings Limited | Administrative & support | 2013 |
| Magnolia SCC Ltd | Professional & scientific | 2021 |
| Maidens LLC Limited | Health & social care | 2017 |
| Mail and Sail Limited | Transport & logistics | 2003 |
| Majestic Spaces Ltd | Professional & scientific | 2023 |
| Makara Muay Thai Ltd | Arts & recreation | 2024 |
| Make Heaven Design Ltd | Construction | 2025 |
| Makley Motor Specialists Ltd | Wholesale & retail | 2015 |
| Malcolm Kendall Plumbing and Heating Ltd | Construction | 2012 |
| MAN and Van Movers Limited | Water & waste | 2025 |
| Manble Ltd | Real estate | 2003 |
| Mango 180 Limited | Hospitality | 2023 |
| Manj & Sons Ltd | Wholesale & retail | 2024 |
| Mankey Mind Ltd | Education | 2024 |
| Manor Developments (Hampshire) Limited | Construction | 2014 |
| Manor House Consulting Limited | Information & communication | 2014 |
| Manor Projects Ltd | Construction | 2020 |
| Manorthorn Ltd | Extraterritorial | 2013 |
| Mansbridge Holdings Ltd | Professional & scientific | 2020 |
| Manson Plumbing & Heating Limited | Construction | 2022 |
| Mant & Co. Accountants Ltd. | Professional & scientific | 2016 |
| Mantarini Limited | Financial services | 2025 |
| Mantej Properties Limited | Real estate | 2026 |
| Manucourt Limited | Health & social care | 1996 |
| Manzanita Investments Ltd | Real estate | 2025 |
| Manzoor Investments Limited | Real estate | 2025 |
| Mapledean Developments Limited | Construction | 1991 |
| Mapledean Special Projects Limited | Construction | 2000 |
| Maples (Fair Oak) Residents Company Limited | Professional & scientific | 2007 |
| Margemm Limited | Other services | 2025 |
| Maria Jones Funeral Directors Limited | Other services | 2018 |
| Marina Life Homes Limited | Real estate | 2010 |
| Marine Electrical Excellence UK Ltd | Construction | 2025 |
| Marineware Limited | Wholesale & retail | 1986 |
| Mario Drylining Ltd | Construction | 2017 |
| Maritime Project Support Ltd | Professional & scientific | 2006 |
| Maritime Technical Solutions Limited | Professional & scientific | 2011 |
| Mark & K Limited | Construction | 2023 |
| Mark Bulley Limited | Financial services | 2002 |
| Mark Sainsbury Builder Limited | Construction | 2003 |
| Mark Sayers Limited | Information & communication | 2013 |
| Markhor Hub Ltd | Wholesale & retail | 2025 |
| Markus Carlos Ltd | Real estate | 2024 |
| Marley Enterprises (Roller Doors) Limited | Manufacturing | 2003 |
| Maroux Limited | Professional & scientific | 2025 |
| Marrazzi Interiors Ltd | Construction | 2022 |
| Marstela & Vinkier Limited | Administrative & support | 2018 |
| Martencroft Limited | Financial services | 2025 |
| Martin (East Boldre) Limited | Wholesale & retail | 1961 |
| Martin G. Burt Ltd. | Construction | 2003 |
| Martin Goodwin Associates Limited | Professional & scientific | 2013 |
| Martin Holdings (Andover) Limited | Administrative & support | 2023 |
| Martin J Raybould Limited | Professional & scientific | 2003 |
| Martin James Homes LLP | | 2017 |
| Martin Walls Equine D Services Ltd | Other services | 2013 |
| Martyn & Richards Limited | Professional & scientific | 2024 |
| Marvel Paving and Construction Ltd | Construction | 2019 |
| Marwell Motor Company Limited | Wholesale & retail | 2010 |
| Marweta Ltd | Wholesale & retail | 2025 |
| MAS Builders New Forest Ltd | Construction | 2024 |
| Masala Care Limited | Hospitality | 2022 |
| Maschio Consulting Ltd | Professional & scientific | 2025 |
| Mason-Smith Limited | Professional & scientific | 2006 |
| Mast Innovations Ltd | Construction | 2022 |