| Mama's Kitchen (Southampton) Ltd | Wholesale & retail | 2019 |
| Mama's Restaurant Ltd | Hospitality | 2025 |
| Mamacita Southampton Ltd | Hospitality | 2025 |
| Mambo Ltd | Information & communication | 2011 |
| Mambo Private Ltd | Administrative & support | 2024 |
| Mammoth Logistics Ltd | Transport & logistics | 2025 |
| Mammoth Mobiles Limited | Wholesale & retail | 2019 |
| MAN Barbershop Limited | Other services | 2016 |
| MAN of Action Limited | Transport & logistics | 2018 |
| Manage Complete Lettings Ltd | Real estate | 2025 |
| Management (Eastleigh) Nutbeem Limited | Households | 1984 |
| Manak Records Ltd | Professional & scientific | 2024 |
| Manali Kitchen Limited | Hospitality | 2024 |
| Manasoja Properties Limited | Real estate | 2019 |
| Mandair Care Homes Limited | Health & social care | 2021 |
| Mandair Estates Ltd | Real estate | 2026 |
| Mandair Limited | Professional & scientific | 2000 |
| Mandair Property Holdings Ltd | Real estate | 2019 |
| Mandala River Limited | Professional & scientific | 2015 |
| Mandalov L&D Ltd | Hospitality | 2023 |
| Mandara Properties Ltd | Real estate | 2024 |
| Mandatry UK Limited | Information & communication | 2026 |
| Mandrews PUB Company Limited | Hospitality | 2018 |
| Maneno Consulting Limited | Professional & scientific | 2004 |
| Mangalya Ltd | Wholesale & retail | 2025 |
| Mangang UK (ITS NOT Weak to Speak) CIC | Health & social care | 2020 |
| Mangmi Ltd | Other services | 2016 |
| Mango 27 LLP | | 2007 |
| Mango Solutions Limited | Professional & scientific | 2025 |
| Mango Surfing Limited | Wholesale & retail | 2019 |
| Mangta Group Limited | Financial services | 2024 |
| Manie Ltd | Professional & scientific | 2019 |
| Manly PIE Company Limited | Hospitality | 2021 |
| Mann Builders Group Ltd | Construction | 2021 |
| Mann Made Designs Limited | Information & communication | 2005 |
| Mann Retail Limited | Wholesale & retail | 2026 |
| Mann Shoes Ltd | Wholesale & retail | 2024 |
| Mannequin International Ltd | Information & communication | 2025 |
| Manns & Manns Limited | Real estate | 2008 |
| Manor Bindery Limited(The) | Manufacturing | 1976 |
| Manor Farm Offices Limited | Professional & scientific | 2001 |
| Manor Grange (Old Netley) Limited | Households | 2013 |
| Manor Heights Management Company Limited | Households | 1988 |
| Manor Lane Media Limited | Professional & scientific | 2020 |
| Manor Life (Haslemere) Limited | Health & social care | 2025 |
| Manor Life (Poole) Limited | Health & social care | 2023 |
| Manor Life (Torquay) Limited | Health & social care | 2025 |
| Manor Life (Winchester) Limited | Health & social care | 2023 |
| Manor Life Group Limited | Professional & scientific | 2025 |
| Manor Life Investments Limited | Financial services | 2012 |
| Manor Life Limited | Professional & scientific | 2025 |
| Manor Windows of Bitterne Limited | Manufacturing | 2018 |
| Manorton E G B Limited | Financial services | 2023 |
| Manos Trans Ltd | Transport & logistics | 2015 |
| Mans Abode Limited | Real estate | 2023 |
| Mansell Ward Ltd | Information & communication | 2013 |
| Manser Group Ltd | Construction | 2019 |
| Manshree Ltd | Real estate | 2022 |
| Mansour Maintenance Limited | Construction | 2013 |
| Mantella Ltd. | Information & communication | 2015 |
| Mantle Labs Limited | Information & communication | 2016 |
| Mantra Aromatics Ltd | Wholesale & retail | 2025 |
| Mantraya Limited | Wholesale & retail | 2025 |
| Manual Barbers Ltd | Other services | 2024 |
| Manzil Homes Ltd | Real estate | 2021 |
| Manzils Restaurant Ltd | Hospitality | 2016 |
| Maobab Projects Limited | Professional & scientific | 2017 |
| MAP Room Limited | Professional & scientific | 2012 |
| Mapamond Constructions Ltd | Construction | 2017 |
| Mapbor Limited | Hospitality | 2019 |
| Mapi Logistics Ltd | Administrative & support | 2017 |
| Maple Court Property Management (Bromborough) Limited | Households | 2006 |
| Maple Park Homes Limited | Real estate | 2017 |
| Maple Trees (Southampton) Management Company Limited | Households | 1998 |
| Maplelane Limited | Professional & scientific | 2024 |
| Maps Heating Ltd | Construction | 2021 |
| MAR Quantity Surveying Ltd | Professional & scientific | 2020 |
| Mar&Wiol Ltd | Transport & logistics | 2017 |
| Marblar Limited | Professional & scientific | 2012 |
| Marble Accounting Limited | Professional & scientific | 2019 |
| Marble Stone Developments Limited | Construction | 2026 |
| Marblesea Limited | Hospitality | 1975 |
| Marbra Ltd | Wholesale & retail | 2023 |
| Marc Badua Samson Limited | Health & social care | 2014 |
| Marc Bishop Family Investments Ltd | Wholesale & retail | 2022 |
| Marc Bradbury Holistic Psychotherapy Ltd | Health & social care | 2022 |
| Marc John Charles Ltd | Extraterritorial | 2024 |
| March and Hare Group Limited | Professional & scientific | 2013 |
| March and Hare Limited | Professional & scientific | 2025 |
| March END Carpentry Ltd | Construction | 2007 |
| March Hair Limited | Other services | 2003 |
| Marchevici Ltd | Transport & logistics | 2021 |
| Marchwood Candles Ltd | Wholesale & retail | 2022 |
| Marchwood Childcare Ltd | Education | 2020 |
| Marchwood Construction (Investment) Company Limited | Real estate | 1984 |
| Marchwood Holdings Limited | Financial services | 2014 |
| Marchwood Motorways Limited | Transport & logistics | 1995 |
| Marchwood Motorways Taxis Limited | Transport & logistics | 1996 |
| Marcin Greglak Ltd | Transport & logistics | 2020 |
| Marcin Marine Services Ltd | Professional & scientific | 2018 |