| Marine Super Store Limited | Wholesale & retail | 1993 |
| Marinescope Taxonomy Ltd. | Professional & scientific | 2018 |
| Mario Properties Ltd | Real estate | 2022 |
| Marion Crescent Property Limited | Real estate | 2016 |
| Marizvikuru Properties Ltd. | Real estate | 2013 |
| Mark Covell Limited | Professional & scientific | 2011 |
| Mark Howe Plumbing & Heating Limited | Construction | 1998 |
| Mark Kavanagh Ltd | Extraterritorial | 2024 |
| Mark Kennett Plumbing & Heating Ltd | Construction | 2012 |
| Mark Power Consulting Limited | Professional & scientific | 2020 |
| Mark Rimmer Decor Ltd | Construction | 2024 |
| Markaz Ltd | Hospitality | 2014 |
| Market Traction International Ltd | Professional & scientific | 2020 |
| Marketing Professionals Limited | Professional & scientific | 2022 |
| Marketscan Limited | Administrative & support | 1971 |
| Markides Associates Employee Ownership Trustees Limited | Professional & scientific | 2020 |
| Markides Associates Limited | Professional & scientific | 2016 |
| Markings and Parking Bays Ltd | Transport & logistics | 2025 |
| Marley and Brothers Ltd | Construction | 2026 |
| Marlivo Ltd | Construction | 2026 |
| Marmalade Sky Limited | Manufacturing | 2014 |
| Marmion Investments Limited | Real estate | 2013 |
| Marmion Properties Ltd | Real estate | 2018 |
| Marne Fabrications Limited | Construction | 2014 |
| Marnetra Limited | Administrative & support | 2007 |
| Maroochy Limited | Real estate | 2017 |
| Marsh Construction Limited | Construction | 2025 |
| Marshall Johnson Holdings Limited | Financial services | 2011 |
| Marshlands Spur Limited | Real estate | 2018 |
| Marsoftware Limited | Administrative & support | 2009 |
| Marta Locum Ltd | Professional & scientific | 2018 |
| Martin Ralph Group Holdings Limited | Financial services | 2026 |
| Martin Ralph Group Limited | Professional & scientific | 2012 |
| Martin Ralph Land Consultants Ltd | Professional & scientific | 2012 |
| Martin Ralph M & E Engineers Ltd | Professional & scientific | 2012 |
| Martin the Milkman Limited | Wholesale & retail | 2013 |
| Martine Elizabeth Parry Limited | Extraterritorial | 2025 |
| Mary Rose Court Management (Southsea) Limited | Households | 1987 |
| Mary Rose Trading Limited | Wholesale & retail | 1979 |
| Mary Rose Trust(The) | Education | 1979 |
| MAS Investment Properties Limited | Real estate | 2017 |
| MAS Maintenance Limited | Construction | 2021 |
| MAS44 Ltd | Financial services | 2025 |
| Masala Lounge Food Service Ltd | Hospitality | 2019 |
| Masca Limited | Construction | 2019 |
| Mash Eagles Ltd | Administrative & support | 2024 |
| Mastercovers Limited | Manufacturing | 2003 |
| Masters Maintenance Ltd | Construction | 2023 |
| Masterton Roofing Limited | Construction | 2021 |
| Mat.Locum Ltd | Wholesale & retail | 2022 |
| Match Accounting Limited | Professional & scientific | 2013 |
| Mathematics of Self Ltd | Arts & recreation | 2015 |
| Matt Thomson Ltd | Construction | 2011 |
| Matted Retail Limited | Wholesale & retail | 2015 |
| Matthew Charles Motoring Collective Limited | Administrative & support | 2025 |
| Matthews Electrical Engineers Limited | Construction | 2003 |
| Mattopia Ltd | Information & communication | 2014 |
| Maud Sinclair Limited | Real estate | 2012 |
| Maverick Global Food Ltd | Hospitality | 2026 |
| MAW Rendering Limited | Construction | 2025 |
| MAX Capital Trading Ltd | Professional & scientific | 2024 |
| MAX KR Ltd | Wholesale & retail | 2018 |
| MAX Management Consultancy Ltd | Construction | 2024 |
| Maxen Homes Limited | Real estate | 2016 |
| Maxi Skips Limited | Water & waste | 2000 |
| Maximilian Magic Ltd | Arts & recreation | 2018 |
| Maximize Your Time Limited | Administrative & support | 2010 |
| Maximum Car Credit Limited | Financial services | 2015 |
| Maximum Property(South Coast) Developments Ltd | Construction | 2023 |
| Maximus Home Build Limited | Construction | 2018 |
| Maxipro Limited | Professional & scientific | 2014 |
| Maxitech Networks Limited | Information & communication | 2001 |
| Maxwell One Ltd | Wholesale & retail | 2024 |
| MAY Cove Ltd | Real estate | 2025 |
| MAY Painters Ltd | Construction | 2025 |
| Maya & Pati Limited | Wholesale & retail | 2012 |
| Mayamari Ltd | Health & social care | 2024 |
| Mayfair Homes ( Southern) Limited | Construction | 2023 |
| Mayfair Marketing Limited | Administrative & support | 2014 |
| Mayfield Jays Limited | Manufacturing | 1994 |
| Mayfield Records Ltd | Information & communication | 2014 |
| Mayfield Sales & Distributions Ltd | Wholesale & retail | 2026 |
| Mayflower Health Investment Ltd | Health & social care | 2025 |
| Mayflower Mews Management Company Limited | Other services | 2012 |
| Mayhall & Waterhouse Limited | Real estate | 2020 |
| Mayhall Group Limited | Wholesale & retail | 2020 |
| Maylings Properties Limited | Real estate | 2017 |
| Mayo & SON Ltd | Construction | 2016 |
| Mayo Electrical Contractors Limited | Construction | 2006 |
| MB Developments (Southern) Limited | Construction | 2020 |
| MB Medical Solutions Ltd | Administrative & support | 2014 |
| MB Studio Limited | Professional & scientific | 2009 |
| MB Utilities Ltd | Construction | 2011 |
| MBB Holding Group Limited | Financial services | 2023 |
| MBB Property Services Limited | Professional & scientific | 2018 |
| MBB Ventures Limited | Real estate | 2014 |
| Mbb-Consulting Group Limited | Professional & scientific | 2017 |
| Mbbm Events Limited | Administrative & support | 2024 |
| Mbbp Investments Ltd | Real estate | 2024 |
| MBF Consultancy Services Limited | Health & social care | 2013 |