| Malent Limited | Professional & scientific | 2005 |
| Mallards (Chichester) Management Company Limited | Households | 1989 |
| Mamo Fenech Ltd | Health & social care | 2012 |
| Management Pocketbooks Limited | Information & communication | 1991 |
| Mandala Health Ltd | Wholesale & retail | 2023 |
| Mandc Trustee (1) Limited | Financial services | 2023 |
| Mandc Trustee (2) Limited | Financial services | 2023 |
| Mango Source Ltd | Real estate | 2014 |
| Mani Naghibi Enterprises Limited | Households | 2023 |
| Mani Naghibi Limited | Health & social care | 2021 |
| Manna Asian Food Ltd | Manufacturing | 2023 |
| Mannion Marine Limited | Professional & scientific | 2018 |
| Manor Barns (Twyford) Management Company Ltd | Real estate | 2016 |
| Manor Court Residential Management Limited | Households | 2020 |
| Manor Electrical & Garage Services Limited | Construction | 2014 |
| Manor Farm (Fyfield) Limited | Real estate | 2024 |
| Manor Flats 5 - 8 (Twyford) Limited | Households | 2019 |
| Many Paws Grooming Salon Limited | Other services | 2025 |
| Mapa Studios Ltd | Wholesale & retail | 2025 |
| Mapland Properties Limited | Construction | 2003 |
| Maple Fields (Odiham) Management Company Limited | Households | 2021 |
| Maple Land Profits Ltd | Real estate | 2024 |
| Maple Lane Arts Ltd | Wholesale & retail | 2020 |
| Maploom Limited | Information & communication | 2018 |
| Marasmius Limited | Professional & scientific | 2016 |
| Marbas Group Limited | Professional & scientific | 2015 |
| March Hair (North Baddesley) Limited | Other services | 2015 |
| Marchstone Construction Ltd | Construction | 2021 |
| Margaux Winchester Ltd | Hospitality | 2024 |
| Maria Angela Collection Limited | Hospitality | 2020 |
| Marine Business Consultants Limited | Professional & scientific | 2021 |
| Marine Ecosystems Regeneration Ltd | Agriculture & fishing | 2024 |
| Marine Oxygen Solutions Limited | Construction | 2024 |
| Marjoribanks Consulting Ltd | Construction | 2016 |
| Mark Barrow Limited | Administrative & support | 2000 |
| Mark Eslick Graphics Limited | Administrative & support | 2006 |
| Mark Humphrey Limited | Professional & scientific | 2000 |
| Mark's Fast Food Bar Limited | Hospitality | 2012 |
| Market Measures Holdings Limited | Financial services | 2023 |
| Market Measures Limited | Professional & scientific | 1986 |
| Marketcity Limited | Extraterritorial | 1989 |
| Marketing & Lead Generation Ltd | Administrative & support | 2025 |
| Marketing Harmony Limited | Professional & scientific | 2015 |
| Marklyn (UK) Limited | Arts & recreation | 2008 |
| Marla Custom Blinds Limited | Manufacturing | 2004 |
| Marlow Cars Limited | Wholesale & retail | 2004 |
| Marlow Walk Management Company Limited | Households | 2023 |
| Marprof Limited | Information & communication | 2017 |
| Marrs Inns Ltd | Hospitality | 2013 |
| Marse Limited | Hospitality | 2021 |
| Marshall Lung Services Limited | Health & social care | 2018 |
| Marshallsound Ltd | Wholesale & retail | 2000 |
| Marste Engineering Limited | Professional & scientific | 2008 |
| Marston Gate RTM Company Limited | Households | 2009 |
| Martin Allman Architecture and Design Ltd | Professional & scientific | 2005 |
| Martin and Company (Company Secretaries) Limited | Professional & scientific | 1997 |
| Martin and Company (Nominees) Limited | Professional & scientific | 1997 |
| Martin and Company Accountants Limited | Professional & scientific | 2009 |
| Martin and Company Audit Limited | Professional & scientific | 2017 |
| Martine Garabette Limited | Professional & scientific | 2024 |
| Marwell Services Limited | Wholesale & retail | 1969 |
| Marwell Wildlife | Professional & scientific | 1978 |
| Mary Tavy Care Limited | Health & social care | 2018 |
| Masker Architects Ltd | Professional & scientific | 2020 |
| Mason's Yard Limited | Professional & scientific | 2025 |
| Masonbrook Group Limited | Professional & scientific | 1986 |
| Masonbrook Industrials Limited | Extraterritorial | 2000 |
| Masonbrook Limited | Construction | 1973 |
| Massey Smart Partnership Ltd | Professional & scientific | 2023 |
| Masseys Winchester Ltd | Hospitality | 2024 |
| Master Entertainment Ltd | Information & communication | 2021 |
| Masterplan Capital Ltd | Real estate | 2025 |
| Masters Anaesthetics Ltd | Health & social care | 2020 |
| Masters Real Estate Investment Limited | Real estate | 2017 |
| Mastro Group Hospitality Ltd | Hospitality | 2026 |
| Mata Annapurna Ltd | Wholesale & retail | 2021 |
| Material Group Limited | Professional & scientific | 2017 |
| Mathom House Investments Limited | Administrative & support | 2018 |
| Matt Chamberlain Associates Limited | Construction | 2018 |
| Matt Holt Productions Limited | Information & communication | 2008 |
| Matter of Seconds Limited | Information & communication | 2022 |
| Matterley Farming | Agriculture & fishing | 2017 |
| Mauvecom Limited | Manufacturing | 1999 |
| Maven Cowork Ltd | Administrative & support | 2019 |
| MAX Davidson Limited | Extraterritorial | 2016 |
| Maxigain Residents Management Limited | Households | 1987 |
| Maxx Investments Limited | Professional & scientific | 2009 |
| Maxx Media Ltd | Professional & scientific | 2018 |
| Maxxer UK Ltd. | Information & communication | 2011 |
| MAY 2 Build Limited | Construction | 2022 |
| MAY Avenue Capital Ltd | Financial services | 2019 |
| Mayflower Winchester Limited | Hospitality | 2015 |
| Mayfly Homes Ltd | Construction | 2007 |
| Mayhill Estates Ltd | Real estate | 2020 |
| MB Recruit Ltd | Administrative & support | 2023 |
| Mberta C.I.C. | Hospitality | 2024 |
| MCA - Kingstone Limited | Administrative & support | 2004 |
| MCB Accounting Services Ltd | Professional & scientific | 2015 |
| MCC Plus Ltd | Administrative & support | 2022 |
| Mccowen Farms Utilities Limited | Extraterritorial | 2009 |