| M C Property Investment and Development Limited | Real estate | 2017 |
| M Finch & SON Ltd | Construction | 2018 |
| M Groupe Ltd | Wholesale & retail | 2021 |
| M LAL Properties Ltd | Real estate | 2023 |
| M P Seven Limited | Professional & scientific | 2011 |
| M S Autos Ltd | Wholesale & retail | 2021 |
| M S Import Ltd | Wholesale & retail | 2025 |
| M View Management Ltd | Households | 2026 |
| M&M Vehicle Solutions Ltd | Wholesale & retail | 2016 |
| M.A. Mcfarlane Brickwork Contractors Limited | Administrative & support | 2005 |
| M.J.W Design Limited | Administrative & support | 2025 |
| M.R Dance Studio Ltd | Arts & recreation | 2022 |
| M.T.D. Formwork Limited | Construction | 1986 |
| M.V & M.Z Limited | Administrative & support | 2013 |
| M.V.Z. Ltd | Construction | 2019 |
| M11 Ltd | Wholesale & retail | 2025 |
| M2 Logistics and Clearance Ltd | Transport & logistics | 2024 |
| M3 Fundraising Limited | Other services | 2023 |
| MA Cleaning Ltd | Administrative & support | 2025 |
| MA Connected Intelligence Limited | Information & communication | 2025 |
| MA Technology Limited | Manufacturing | 2023 |
| MAA Engineering Limited | Professional & scientific | 2011 |
| Maastran Ltd | Information & communication | 2019 |
| MAB Construction Scenery Ltd | Construction | 2023 |
| Mabel Engage Ltd | Information & communication | 2026 |
| Mabel Insights Ltd | Information & communication | 2023 |
| Mabs&Co Handyman and Property Services Ltd | Construction | 2024 |
| Macdermid Actium, Ltd | Professional & scientific | 2005 |
| Macdermid Continental Investments Limited | Professional & scientific | 2007 |
| Macdermid Europe Limited | Professional & scientific | 1920 |
| Macdermid European Finance Limited | Professional & scientific | 2023 |
| Macdermid Graphics Solutions UK Limited | Wholesale & retail | 2020 |
| Macdermid Performance Acquisitions Ltd | Financial services | 2015 |
| Macdermid Performance Solutions Services Limited | Professional & scientific | 2012 |
| Macdermid Performance Solutions UK Limited | Manufacturing | 1976 |
| Macestep Limited | Construction | 1977 |
| Machap Holdings Limited | Financial services | 2020 |
| Maciel Hair Studio Ltd | Other services | 2026 |
| Macleod Simmonds Ltd | Professional & scientific | 2008 |
| Macleod Simmonds Software Solutions Limited | Wholesale & retail | 2017 |
| Maclinic Ltd | Other services | 2014 |
| Macw Developments Limited | Construction | 2011 |
| Madd Catering Limited | Hospitality | 2017 |
| Made by Stella Ltd | Information & communication | 2020 |
| Made in Britain Trade Centres Limited | Administrative & support | 2015 |
| Made Real Ltd | Professional & scientific | 2000 |
| Madelec (U.K.) Limited | Professional & scientific | 2006 |
| Madlins Corporate 1 Ltd | Financial services | 2025 |
| Madlins Corporate 2 Ltd | Financial services | 2025 |
| Madlins LLP | | 2015 |
| Maestra Education Services Ltd | Education | 2012 |
| Magelea Limited | Professional & scientific | 2012 |
| Maggie Treanor Designs Limited | Wholesale & retail | 2007 |
| Magic Cleaning Guildford Ltd | Administrative & support | 2014 |
| Magic Hub Ltd | Information & communication | 2023 |
| Magic VFX Limited | Other services | 2011 |
| Magnet Schultz Limited | Manufacturing | 1967 |
| Magnolia Gardens Ltd | Administrative & support | 2014 |
| Magnolia Groundworks Limited | Professional & scientific | 2016 |
| Magnum Airport Cars Ltd | Transport & logistics | 2024 |
| Magnum Opus Limited | Hospitality | 2004 |
| Mahwen Ltd | Professional & scientific | 2024 |
| Maid for Each Other Ltd | Administrative & support | 2021 |
| Maidstone Business Centre Ltd | Real estate | 2024 |
| Mail Boxes ETC. (Woking) Limited | Manufacturing | 2009 |
| Main Contracts (London) Limited | Construction | 2012 |
| Mainpoint Consultants Limited | Professional & scientific | 1998 |
| Maintain London Ltd | Construction | 2019 |
| Maison Mumbai Co Ltd | Hospitality | 2024 |
| Majestic Performance Ltd Limited | Administrative & support | 2025 |
| Majestorn Ltd | Professional & scientific | 2024 |
| Majic AI Ltd | Information & communication | 2025 |
| Makalu Homes Ltd | Real estate | 2025 |
| Make Change Happen Limited | Other services | 2006 |
| Make IT Happen IT Services Limited | Information & communication | 2014 |
| Making Meadows Ltd | Professional & scientific | 2021 |
| Making Milestones Ltd | Professional & scientific | 2012 |
| Malakof Ltd | Other services | 2020 |
| Maliackan Ltd | Hospitality | 2022 |
| Malik Builders Limited | Construction | 2020 |
| Mallams Family Office Limited | Professional & scientific | 2014 |
| Mallard Management Limited | Households | 2006 |
| Malt & RYE Ltd | Wholesale & retail | 2017 |
| Malthigh Limited | Households | 1984 |
| Mama Organica Ltd | Wholesale & retail | 2016 |
| Manage Consult Procure Limited | Professional & scientific | 2009 |
| Managed Security Solutions Limited | Information & communication | 2001 |
| Manageplaces Limited | Information & communication | 2013 |
| Manawey Developments Limited | Real estate | 1965 |
| Manciple Flats Limited | Households | 2014 |
| Maneo Technology Limited | Information & communication | 2025 |
| Manfi Consulting Limited | Information & communication | 2014 |
| Manfron Solutions Limited | Financial services | 2021 |
| Manicured Gardens Ltd | Administrative & support | 2020 |
| Manicured Lawns Ltd | Administrative & support | 2025 |
| Manifest Technologies Limited | Information & communication | 2014 |
| Mann Technologies Limited | Information & communication | 2016 |
| Manor Meadows Limited | Agriculture & fishing | 2019 |
| Manotte Ltd | Information & communication | 2026 |
| Manro Limited | Professional & scientific | 2024 |