| Maylim EOT Limited | Administrative & support | 2018 |
| Maylim Landscapes Limited | Construction | 2022 |
| Maylim Limited | Construction | 2002 |
| Maylim Properties Limited | Real estate | 2015 |
| MAZ Ecom Ltd | Wholesale & retail | 2024 |
| MB Electrical (Surrey) Ltd | Construction | 2017 |
| Mber.London Limited | Hospitality | 2015 |
| MC Installations Ltd | Construction | 2026 |
| Mccann Groundworks Limited | Construction | 2001 |
| Mclee & Co Ltd | Other services | 2011 |
| Mcloughlin Property Development Ltd | Construction | 2023 |
| Mcpherson Corporations Ltd | Construction | 2020 |
| MDC Signature Interiors Limited | Construction | 2026 |
| MDH Property Investments Limited | Financial services | 2022 |
| MDP Public Finance Associates Limited | Professional & scientific | 2007 |
| ME Group 2XL Ltd | Professional & scientific | 2023 |
| Meadowbank House Limited | Real estate | 2020 |
| Meadowview Communal Management Ltd | Real estate | 2026 |
| Measured Survey Solutions Limited | Professional & scientific | 2007 |
| Meath Green Lane (Freehold) Ltd | Households | 2011 |
| Meath Green Lane Maintenance Company Limited | Households | 1976 |
| Mechi Reality Ltd | Real estate | 2020 |
| Medcalluk Limited | Health & social care | 2021 |
| Media & More Contracting Limited | Professional & scientific | 2018 |
| Medigo Health Limited | Health & social care | 2026 |
| Medijamm Ltd | Information & communication | 2026 |
| Medwits Ltd | Health & social care | 2019 |
| Meet and Greet Ltd | Transport & logistics | 2019 |
| Megson Management Limited | Professional & scientific | 2001 |
| Mehen Research Ltd | Information & communication | 2023 |
| Mela Mela Limited | Wholesale & retail | 2007 |
| Meld Energy (Saltend) Ltd | Professional & scientific | 2023 |
| Meld Energy Limited | Professional & scientific | 2020 |
| Mellon Trench Limited | Professional & scientific | 2018 |
| Melville (London) Limited | Administrative & support | 2010 |
| Memskor Ltd | Transport & logistics | 2022 |
| Mensch Limited | Hospitality | 2024 |
| Menticus Ltd | Financial services | 2017 |
| Merchant Princes Company Limited(The) | Information & communication | 1958 |
| Merchants Quarter Limited | Construction | 2006 |
| Meribel Properties Ltd | Hospitality | 2000 |
| Meridian 25 Consulting Ltd | Professional & scientific | 2026 |
| Meridian West London Limited | Wholesale & retail | 2012 |
| MERL1N Ltd | Wholesale & retail | 2022 |
| Merrifield (Wivelsfield) Management Company Limited | Households | 2022 |
| Merrow Asset Management Limited | Real estate | 2011 |
| Merrowhouse Limited | Real estate | 2018 |
| Merryweather Court Limited | Households | 2025 |
| MET Serve Limited | Construction | 2005 |
| Mewstone Financial Services Ltd | Professional & scientific | 2016 |
| Mgkcodes Ltd | Information & communication | 2026 |
| MGP Executive Limited | Professional & scientific | 2015 |
| MGT Broadcast Ltd | Information & communication | 2017 |
| MH Fund Advisors Ltd | Financial services | 2015 |
| MIC ME UP Ltd | Information & communication | 2011 |
| Michael Jones and Associates LLP | | 2005 |
| Michael Rogers LLP | | 2009 |
| Micoh Limited | Extraterritorial | 2022 |
| Micro Green Energy Ltd | Professional & scientific | 2022 |
| Microbiome Minds Limited | Health & social care | 2025 |
| Midmoor Road NO 25 Limited | Real estate | 2005 |
| Mieres & Co Ltd | Professional & scientific | 2015 |
| Mika Investments Ltd | Financial services | 2024 |
| Milestand Limited | Professional & scientific | 2018 |
| Millbrook NO 1 Limited | Construction | 1980 |
| Miller Logistics (Gatwick) Limited | Transport & logistics | 2011 |
| Miller Logistics Limited | Transport & logistics | 1999 |
| Millets Farm and Kitchen Ltd | Agriculture & fishing | 2025 |
| Mills Meade Investments Limited | Real estate | 2018 |
| Millsted Care Ltd | Health & social care | 1996 |
| Millsted Property Ltd | Real estate | 2021 |
| Millsted Training and Consultancy Ltd | Education | 2018 |
| Minded CPD Limited | Education | 2022 |
| Minded Professional Training Limited | Education | 2022 |
| Mindful Movement Pilates Limited | Education | 2024 |
| Mindseye Lighting Ltd | Professional & scientific | 1999 |
| Minerva Security Advisory Ltd | Information & communication | 2025 |
| Minor ARC Holdings Limited | Real estate | 2026 |
| Minvision Limited | Wholesale & retail | 2007 |
| Miraled Capital Limited | Real estate | 2025 |
| Missy Studios Limited | Professional & scientific | 2025 |
| Mityko Limited | Professional & scientific | 2018 |
| Miwk Publishing Ltd | Wholesale & retail | 2011 |
| Mnjr Ltd | Health & social care | 2016 |
| MNK Services Ltd | Administrative & support | 2017 |
| Mobile Guardian Limited | Information & communication | 2010 |
| Mobisoft Corporation Ltd | Administrative & support | 2009 |
| MOD (Pinstone Street) Limited | Construction | 2002 |
| MOD REV Limited | Manufacturing | 2026 |
| Model Village Ltd | Real estate | 1996 |
| Modern Shelving Ltd | Manufacturing | 2025 |
| Modest Dragon Ltd | Transport & logistics | 2024 |
| Modise Limited | Health & social care | 2024 |
| Moletor Ltd | Real estate | 2022 |
| MON Amie Organics Ltd | Wholesale & retail | 2018 |
| Monom Ltd | Administrative & support | 2003 |
| Montague Investments Limited | Construction | 2004 |
| Moon Hall Assessment Centre Limited | Education | 2024 |
| Moon Hall International Limited | Education | 2024 |
| Moon Hall Schools Educational Trust | Education | 1990 |