| Mackamiff Limited | Real estate | 2018 |
| Mackenzie Landscapes Limited | Administrative & support | 2002 |
| Macods Limited | Construction | 2007 |
| Macro Advertising Limited | Professional & scientific | 2022 |
| Mactrinity Ltd | Information & communication | 2010 |
| Macys Electrical and Property Solutions Ltd | Construction | 2026 |
| Maddison Limited | Professional & scientific | 1986 |
| Made in Ratio Limited | Administrative & support | 2013 |
| Made Just 4 U Gifts Ltd | Wholesale & retail | 2022 |
| Madeley Financial Services Limited | Financial services | 2007 |
| Madge Management Ltd | Professional & scientific | 2019 |
| Madmin Limited | Administrative & support | 2023 |
| Maeclay Jointing Ltd | Construction | 2018 |
| Maepillil Ltd | Other services | 2016 |
| Magahweb Limited | Information & communication | 2020 |
| Magrill Limited | Other services | 2019 |
| Mahant Holdings Ltd | Administrative & support | 2023 |
| Mail Users' Association Limited | Other services | 1976 |
| Mainsail Management Limited | Professional & scientific | 2002 |
| Maison and Jardin Property Management and Investment Limited | Real estate | 2018 |
| Maison DE Bertelli Ltd | Wholesale & retail | 2022 |
| Maison Property Management Ltd | Households | 2017 |
| Majestic Marine Services Ltd | Manufacturing | 2016 |
| Major IT Limited | Information & communication | 2004 |
| MAK Care+ Ltd | Health & social care | 2024 |
| MAK Community Care Limited | Health & social care | 2019 |
| Make Light Work Limited | Information & communication | 2011 |
| Making My Grass Greener Ltd | Other services | 2021 |
| Malaz GB Ltd | Wholesale & retail | 2026 |
| Malbari Limited | Hospitality | 2024 |
| Malik & Co Holdings Ltd | Real estate | 2025 |
| Malthouse Road Properties Ltd | Real estate | 2019 |
| Mama Good to Go Limited | Wholesale & retail | 2025 |
| Mamba Boxing Gym CIC | Other services | 2021 |
| MAN Plus Van Limited | Other services | 2011 |
| Mandelion Estates Limited | Real estate | 2018 |
| Mandelion Freehold Limited | Real estate | 2020 |
| Mandy Puntis Mortgage & Protection Services Ltd | Financial services | 2013 |
| Manfield Consultancy Limited | Other services | 2017 |
| Mango Space Limited | Professional & scientific | 2020 |
| Mannor Real Estate Ltd | Real estate | 2016 |
| Mantlelink Limited | Wholesale & retail | 2024 |
| Manuka Wholefoods Ltd | Wholesale & retail | 2010 |
| MAP Financial Limited | Financial services | 2001 |
| MAP Financial South Limited | Financial services | 2023 |
| Maples Day Nursery Basingstoke Limited | Education | 1998 |
| Marand Solutions Limited | Education | 2020 |
| Marble Academy and Management Limited | Arts & recreation | 2023 |
| Marble Assets Ltd | Real estate | 2023 |
| Marbs Ltd | Other services | 2018 |
| Marengotek Limited | Manufacturing | 2024 |
| Marg Engineering Consultancy Ltd | Professional & scientific | 2025 |
| Maria Caring Ltd | Health & social care | 2019 |
| Maria Franzoni Ltd | Professional & scientific | 2010 |
| Maria Franzoni Ventures Limited | Hospitality | 2024 |
| Marie Court Management Company Limited | Real estate | 1992 |
| Marine Farm Services Limited | Agriculture & fishing | 2020 |
| Mariposa Languages Limited | Information & communication | 2018 |
| Mariya&Co Ltd | Real estate | 2025 |
| Marjen EOT Limited | Financial services | 2023 |
| Marjen Ltd | Professional & scientific | 2011 |
| Marjen Property Management Ltd | Real estate | 2022 |
| Mark Chamberlain Ltd | Arts & recreation | 2023 |
| Mark Duncan Accountancy Ltd | Extraterritorial | 2008 |
| Mark Elverson Services Limited | Real estate | 2015 |
| Mark Graham Financial Services Limited | Other services | 2015 |
| Mark Hill Music Limited | Information & communication | 2025 |
| Mark James Plumbing & Heating Ltd | Construction | 2010 |
| Mark Redman Carpentry Services Ltd | Construction | 2022 |
| Markerching Ltd | Other services | 2016 |
| Marlborough Nakano Ltd | Wholesale & retail | 2023 |
| Marmalade Monkey Limited | Extraterritorial | 2022 |
| Marmalades Hampshire Limited | Wholesale & retail | 2026 |
| Marmion House Limited | Hospitality | 2017 |
| Marriner's Entertainment Ltd | Arts & recreation | 2025 |
| Marriott Sherwell Limited | Professional & scientific | 2016 |
| Marristone Homes Ltd | Construction | 2023 |
| Marsell Property Limited | Real estate | 2022 |
| Marsh Roofing Ltd | Construction | 2025 |
| Marshall Physiotherapy Ltd. | Health & social care | 2017 |
| Marson Enterprises Limited | Construction | 2003 |
| Martin C Hanly Limited | Professional & scientific | 2018 |
| Martin Eaton Limited | Professional & scientific | 2005 |
| Martin Howard Homes Limited | Construction | 2004 |
| Martin Ralph GP Surveyors Ltd | Professional & scientific | 2014 |
| Martin Ralph Limited | Administrative & support | 2007 |
| Martin Ralph Properties Ltd | Real estate | 2018 |
| Martindale Medical Services Limited | Health & social care | 2018 |
| Marula Lodge Limited | Financial services | 2015 |
| Marvance Ltd | Professional & scientific | 2024 |
| Marvic Engineering Products Limited | Manufacturing | 1972 |
| Marware Holdings Ltd | Financial services | 2023 |
| Mary J'S Hair Fashions Limited | Other services | 2019 |
| MAS Flexible Medical Services Ltd | Health & social care | 2013 |
| MAS IG SPV2 Limited | Financial services | 2021 |
| Maslow Data Limited | Administrative & support | 2020 |
| Mason Marsh Developments Ltd | Construction | 2023 |
| Masral Therapy Limited | Professional & scientific | 2010 |
| Massive JIM Ltd | Arts & recreation | 2018 |
| Master Builder Services Ltd | Construction | 2020 |