| Mark Anthony's Personal Training Limited | Arts & recreation | 2003 |
| Mark Batchelor Electrical Services Ltd | Construction | 2014 |
| Mark Black Farming Ltd | Agriculture & fishing | 2011 |
| Mark Burr Associates Limited | Information & communication | 1998 |
| Mark Cole Metal Forming Ltd | Manufacturing | 2007 |
| Mark E Powell Limited | Real estate | 2017 |
| Mark Education Limited | Administrative & support | 1998 |
| Mark Hancock Consulting Limited | Professional & scientific | 2024 |
| Mark Hopkins Car Sales Ltd | Wholesale & retail | 2016 |
| Mark Leavey Design Ltd | Professional & scientific | 2014 |
| Mark Lewis Television Limited | Information & communication | 2009 |
| Mark Mansbridge Property Limited | Real estate | 2019 |
| Mark Nunez Design Limited | Professional & scientific | 2012 |
| Mark Page Services Ltd | Administrative & support | 2016 |
| Mark Pascoe Limited | Manufacturing | 1999 |
| Mark Timothy Connor Ltd | Extraterritorial | 2026 |
| Mark. I-Consulting Ltd | Education | 2022 |
| Markaero Limited | Professional & scientific | 2019 |
| Markay Property Limited | Real estate | 2023 |
| Market Minded Limited | Financial services | 2022 |
| Market Operator Services Limited | Other services | 2014 |
| Market Resources Limited | Transport & logistics | 1993 |
| Markexel Ltd | Information & communication | 2025 |
| Markhairsearle Ltd | Other services | 2022 |
| Markiks Initiative Ltd | Wholesale & retail | 2025 |
| Marklin Food Ltd | Hospitality | 2024 |
| Markos Transport Limited | Transport & logistics | 2014 |
| Mark’S Maintenance Ltd | Professional & scientific | 2024 |
| Marlacourt Limited | Health & social care | 1991 |
| Marlborough House (Southampton) RTM Company Limited | Real estate | 2009 |
| Marlena M.O Hair Limited | Other services | 2024 |
| Marley’S Whisper Ltd | Education | 2025 |
| Marlin Facilities Management Limited | Administrative & support | 2022 |
| Marlin Marine Engineering Ltd | Professional & scientific | 2013 |
| Marlin Motors Ltd | Manufacturing | 2018 |
| Marlo Advisory Ltd | Financial services | 2026 |
| Marm PRS Limited | Real estate | 2018 |
| Marn Corporation Limited | Wholesale & retail | 2025 |
| Marnic Engineering & Property Maintenance Ltd | Professional & scientific | 2012 |
| Marnic Real Estate Ltd | Real estate | 2022 |
| Maroon Photography Limited | Professional & scientific | 2025 |
| Marpal Architectural Aluminium Limited | Wholesale & retail | 2009 |
| Marprof Environmental Limited | Information & communication | 2018 |
| Marriage Sankofa Limited | Health & social care | 2024 |
| Mars Care Limited | Health & social care | 2025 |
| Mars Space Ltd | Professional & scientific | 2007 |
| Marshall & Hargreaves Limited | Real estate | 2016 |
| Marshall Denning 2 LLP | | 2017 |
| Marshall Denning Ltd | Information & communication | 2017 |
| Marshall Elevator Services Ltd | Manufacturing | 2007 |
| Marshall's Property Ltd | Real estate | 2025 |
| Martin & Porter Co. Limited | Construction | 2000 |
| Martin and Dodds Limited | Other services | 1987 |
| Martin Back Homes Limited | Construction | 2019 |
| Martin Brown Carpentry & Joinery Ltd | Construction | 1997 |
| Martin Global Holdings Limited | Professional & scientific | 2017 |
| Martin Glover Engineering Limited | Manufacturing | 2000 |
| Martin Harris Consultants Ltd | Professional & scientific | 2014 |
| Martin Sennett Limited | Administrative & support | 2008 |
| Martina Rose Accounting Ltd | Professional & scientific | 2022 |
| Martina Rose Bookkeeping Ltd | Professional & scientific | 2025 |
| Martlets Consulting Ltd | Professional & scientific | 2025 |
| Marty Removal Ltd | Transport & logistics | 2026 |
| Martyna Charters Limited | Arts & recreation | 2023 |
| Martyna HTS Limited | Wholesale & retail | 2025 |
| Maru/Blue UK Limited | Administrative & support | 2017 |
| Maru/Edr Limited | Administrative & support | 2005 |
| Maruti Fashion Ltd | Wholesale & retail | 2026 |
| Marvellous Designs Limited | Extraterritorial | 2007 |
| Marwik Ltd | Administrative & support | 2022 |
| Mary's Must Haves Ltd | Wholesale & retail | 2024 |
| Maryal Building Services Limited | Construction | 2012 |
| Maschio & Soames IP Limited | Administrative & support | 2012 |
| Mashtech Logistics Limited | Wholesale & retail | 2024 |
| Masignaturehouse Ltd | Wholesale & retail | 2026 |
| Maskala Limited | Wholesale & retail | 2022 |
| Masked Potential Logistics Limited | Transport & logistics | 2015 |
| Masked Potential Media Ltd | Professional & scientific | 2025 |
| Maskglobe Limited | Households | 1983 |
| Mason & Vaughan Group Ltd | Professional & scientific | 2012 |
| Mason Bricklaying Ltd | Construction | 2024 |
| Maspi Ventures Ltd | Information & communication | 2022 |
| Mass Infotech Ltd | Information & communication | 2024 |
| Massagetronic Limited | Wholesale & retail | 2021 |
| Massey Administration Limited | Other services | 2014 |
| Mast Architectural Interiors Limited | Other services | 2023 |
| Mast Collective Ltd | Hospitality | 2025 |
| Master Driveways Ltd | Administrative & support | 2026 |
| Master Installations Ltd | Construction | 2011 |
| Master IT Firm Ltd | Information & communication | 2025 |
| Master Productions Ltd. | Information & communication | 2012 |
| Master SHA TAO Calligraphy Art Ltd | Education | 2025 |
| Master Shifu Ltd | Arts & recreation | 2026 |
| Master Value Ltd | Wholesale & retail | 2023 |
| Master-Craft of Lymington Limited | Other services | 2010 |
| Mastercraft Decorative Mouldings Limited | Construction | 2010 |
| Mastercraft Projects Ltd | Construction | 2024 |
| Masterit Driving School Ltd | Education | 2021 |
| Masthor Heating & Electrical Limited | Manufacturing | 1992 |
| Masthor Trading Limited | Wholesale & retail | 1985 |