| Mascarenhas Property Limited | Real estate | 2019 |
| Mascot Learning Academy Limited | Education | 2016 |
| Masei Trading Limited | Other services | 2019 |
| Maskenth Limited | Professional & scientific | 2016 |
| Masood Travels & Tours Ltd | Administrative & support | 2020 |
| Mass Construction Limited | Construction | 2023 |
| Mass London Ltd | Other services | 2021 |
| Masscar Ltd | Wholesale & retail | 2025 |
| Massienda Ltd | Real estate | 2019 |
| Massive Creation Limited | Arts & recreation | 1998 |
| Massive Miniatures Limited | Information & communication | 2016 |
| Master Blinds and Curtains Ltd | Wholesale & retail | 2023 |
| Masters in Cleaning Unique Ltd | Administrative & support | 2022 |
| Masterson's Events Ltd | Extraterritorial | 2025 |
| Masterson's Ice Cream Ltd | Extraterritorial | 2025 |
| Mata Electrical Group UK Limited | Construction | 2025 |
| Mataar Ltd | Real estate | 2023 |
| Matada Limited | Real estate | 2022 |
| Matan Property Solutions Limited | Households | 2025 |
| Matchstrong Limited | Wholesale & retail | 1986 |
| Matchup Games Ltd | Information & communication | 2024 |
| Mateen Mirza Cafe 786 Limited | Other services | 2005 |
| Matei AL Ltd | Construction | 2023 |
| Matei Tax Advising Ltd | Professional & scientific | 2025 |
| Mateo Consulting Ltd | Professional & scientific | 2014 |
| Mathias Franke Limited | Professional & scientific | 2009 |
| Matlock Court N.W.8 Management Company Limited | Households | 1978 |
| Matrix Building & Civil Engineering Partners Limited | Professional & scientific | 2001 |
| Matrix Machine Tool (Coventry) Limited | Manufacturing | 2003 |
| Matrix Trade Centre Limited | Real estate | 2014 |
| Matt Armstrong Limited | Information & communication | 2015 |
| Matt White Consulting Limited | Information & communication | 2025 |
| Matt&Ianiosif Ltd | Construction | 2024 |
| Matthew Kentridge Strategic Counsel Limited | Professional & scientific | 2021 |
| Maverick and Goose Ltd | Professional & scientific | 2025 |
| Mawaddah Medical Ltd | Health & social care | 2013 |
| Mawhood Households Limited | Wholesale & retail | 2018 |
| MAX Cutz Limited | Other services | 2023 |
| MAX Travel & Tour Operators Ltd | Transport & logistics | 2018 |
| Max's House PTY Limited | Real estate | 2024 |
| Maxa Trade Ltd | Wholesale & retail | 2025 |
| Maxcaller Ltd | Professional & scientific | 2018 |
| Maxime Events Limited | Other services | 2013 |
| Maximize Logistics Ltd | Wholesale & retail | 2024 |
| Maxin Chicken Loughborough Ltd | Hospitality | 2025 |
| Maxmile Trading Limited | Extraterritorial | 2015 |
| Maxservices Ltd | Administrative & support | 2012 |
| Maxsm Limited | Wholesale & retail | 2021 |
| Maxsure Limited | Real estate | 1989 |
| Maxwell Investment Group Ltd | Real estate | 2025 |
| Maya and Mayson Limited | Hospitality | 2021 |
| Maya Hyperstar Ltd | Wholesale & retail | 2022 |
| Maya's Investments Ltd | Real estate | 2008 |
| Mayarishi Media Ltd | Information & communication | 2017 |
| Mayash Coaches Ltd | Transport & logistics | 2024 |
| Mayash Limited | Transport & logistics | 2021 |
| Mayb Ltd | Administrative & support | 2026 |
| Maybell Property Management Limited | Households | 1996 |
| Maybells Limited | Hospitality | 2012 |
| Mayclach Limited | Professional & scientific | 2014 |
| Mayfair (March) Ltd | Real estate | 2015 |
| Mayfair 500 (Buzzard) Limited | Real estate | 2018 |
| Mayfair 500 (Clarendon) Limited | Real estate | 2016 |
| Mayfair 500 (GB) Limited | Real estate | 2011 |
| Mayfair 500 (Investments) Limited | Other services | 2012 |
| Mayfair 500 Imperial Limited | Real estate | 2017 |
| Mayfair 500 Limited | Professional & scientific | 2011 |
| Mayfair Accountants Ltd | Professional & scientific | 2019 |
| Mayfair Jewellers Limited | Wholesale & retail | 1973 |
| Mayfield Capital Partners Limited | Financial services | 2024 |
| Mayflower Holdings Group Limited | Financial services | 2026 |
| Mayflower Opportunities Ltd | Professional & scientific | 2024 |
| Mayor Estates Limited | Real estate | 2023 |
| Mayor Investments Ltd | Construction | 2025 |
| Mayterra Limited | Professional & scientific | 2018 |
| Maytrium Limited | Administrative & support | 2018 |
| Mazal Investments Ltd | Real estate | 2021 |
| Mazali Ltd | Wholesale & retail | 2021 |
| Mazar City Grill Ltd | Hospitality | 2025 |
| Mazdent Limited | Health & social care | 2022 |
| Mazel Property Investments Limited | Real estate | 2017 |
| Mazel Trading Limited | Wholesale & retail | 1994 |
| MB Coyne Engineering Limited | Professional & scientific | 2022 |
| MB Homewares Ltd | Wholesale & retail | 2024 |
| MB Luxury Travel LLP | | 2021 |
| Mberlin Limited | Administrative & support | 2021 |
| Mbnc Private Limited | Professional & scientific | 2023 |
| MBO London Ltd | Wholesale & retail | 2021 |
| MBS Estates Ltd | Real estate | 2025 |
| MC Imaging Limited | Health & social care | 2019 |
| MC Lukas Limited | Construction | 2017 |
| MC Professional Cleaners Limited | Administrative & support | 2015 |
| MC Security Consultancy Ltd | Wholesale & retail | 2018 |
| Mcaf Builders Ltd | Construction | 2017 |
| Mcaf Consulting Ltd | Construction | 2025 |
| Mcclark Joinery Ltd | Construction | 2019 |
| Mccloskey & Company Ltd | Professional & scientific | 2026 |
| Mccluskey Management Limited | Professional & scientific | 2014 |
| MCF Motors Ltd | Wholesale & retail | 2025 |
| Mcfadden Group Holdings Limited | Financial services | 2026 |