| MET One Limited | Information & communication | 2007 |
| Meta Invest Limited | Real estate | 2019 |
| Metric Spaces Limited | Real estate | 2023 |
| Metrix Developments 1 Limited | Real estate | 2021 |
| Metrix Developments Ltd | Real estate | 2014 |
| Metrix Interiors Limited | Professional & scientific | 2019 |
| MH 4X4 Limited | Wholesale & retail | 2020 |
| MH Site Solutions Ltd | Construction | 2025 |
| MIA Ltd | Transport & logistics | 2023 |
| Michaelis Studio Ltd | Professional & scientific | 2025 |
| Microgen Power Systems Limited | Wholesale & retail | 2019 |
| Microset Limited | Other services | 2011 |
| Midas Estates (Uxbridge) Limited | Real estate | 1982 |
| Middle Associates Ltd. | Financial services | 2019 |
| Mike Cattermole Limited | Information & communication | 2003 |
| Milestone Properties London Limited | Construction | 2019 |
| Milestones London Limited | Hospitality | 2020 |
| Milky Way Investments Limited | Real estate | 2025 |
| Millennial Energy Limited | Energy | 2018 |
| Millennium Fire Protection Limited | Construction | 2001 |
| Miller-Robinson (London) Limited | Professional & scientific | 2015 |
| Millfield Business Park Limited | Real estate | 2023 |
| Milroy Business Management Limited | Professional & scientific | 1996 |
| Milton & Simpson Property Partnership Limited | Real estate | 2017 |
| Mimms Consultancy Services Limited | Construction | 2010 |
| Minchews Fried Chicken Ltd | Hospitality | 2025 |
| Mind Chakra Limited | Wholesale & retail | 2013 |
| Mindel Film Services Limited | Other services | 2015 |
| Mindhealth Psychology Ltd | Health & social care | 2019 |
| Mindology Coaching Ltd | Administrative & support | 2024 |
| Mindology Group Limited | Financial services | 2024 |
| Minoli Design Ltd | Extraterritorial | 2018 |
| Mint House Communications Limited | Information & communication | 2008 |
| Misbourne Marine Management Limited | Transport & logistics | 1989 |
| Misbourne Services Limited | Other services | 2005 |
| Mistral Models Limited | Other services | 2006 |
| Mitcham Bull Limited | Real estate | 2003 |
| MJB Premier Limited | Administrative & support | 2016 |
| MJD Finance Ltd | Professional & scientific | 2018 |
| MJS Health Limited | Financial services | 1997 |
| Mkspub Limited | Professional & scientific | 2014 |
| ML Bespoke Interiors Limited | Extraterritorial | 2023 |
| Mlzh Investments Limited | Real estate | 2022 |
| MM Advisory Services Limited | Professional & scientific | 2011 |
| MM Works Limited | Construction | 2019 |
| MMD UK Holdings Limited | Financial services | 2024 |
| MMF Car Repairs Limited | Construction | 2017 |
| Mmnp Ltd | Professional & scientific | 2018 |
| MN Developments Ltd | Real estate | 2014 |
| Mo'Wax Headz Limited | Extraterritorial | 1995 |
| Mobile Storage UK Finance Limited Partnership | | 2001 |
| Moda DI Uomo Ltd | Wholesale & retail | 2009 |
| Modelon Ltd | Arts & recreation | 2018 |
| Modern Decorating Solutions Ltd | Construction | 2021 |
| Modern Telecommunications Limited | Information & communication | 2016 |
| Modha Group Limited | Financial services | 2019 |
| Modica Limited | Professional & scientific | 2023 |
| Mojo Skin & Haircare Ltd | Administrative & support | 2014 |
| Monaco Homes Limited | Construction | 2016 |
| Monalito Ltd | Extraterritorial | 2023 |
| Monarch Lawn & Landscape Ltd | Administrative & support | 2015 |
| Monirast Group Holdings Ltd | Financial services | 2025 |
| Monirast Ltd | Information & communication | 2025 |
| Monks Horton (South Park) Limited | Households | 2011 |
| Mono Target Investment Limited | Real estate | 2016 |
| Monrae Management Ltd | Arts & recreation | 2021 |
| Monrae Productions Ltd | Information & communication | 2021 |
| Montage Hair Salon Limited | Other services | 2019 |
| Moomoo (UK) Limited | Other services | 2012 |
| Moon Monkey Ltd | Information & communication | 2017 |
| Moonstone Estates Ltd | Real estate | 2018 |
| Morpho Studio Limited | Arts & recreation | 2023 |
| Morris Joint - Line Limited | Construction | 2005 |
| Mortisman LLP | | 2003 |
| Moruzzi Creative Limited | Professional & scientific | 2017 |
| Mota Cycles Rental Ltd | Administrative & support | 2023 |
| Motacycles Garage Ltd | Administrative & support | 2026 |
| Motorbike Shack Limited | Wholesale & retail | 2011 |
| Motum VOX Limited | Health & social care | 2012 |
| Mount (Studland) Limited(The) | Households | 1964 |
| Mount Hill Foods Limited | Manufacturing | 2019 |
| Mount Hill Holdings Ltd | Financial services | 2025 |
| Mount Lavinia Group Limited | Hospitality | 2025 |
| Mountbatten Court (Langley) Management Company Limited | Real estate | 2003 |
| Mour Hotel Limited | Hospitality | 2017 |
| Moutrie Carpentry Limited | Manufacturing | 2021 |
| Move Places Limited | Real estate | 2018 |
| Moveney Limited | Administrative & support | 2022 |
| Mpix Limited | Information & communication | 2018 |
| MR B Commerce Limited | Wholesale & retail | 2025 |
| MR Crusty Ltd | Hospitality | 2021 |
| MRM Property Holdings Ltd | Real estate | 2023 |
| MSC Works Limited | Other services | 2015 |
| Mscd London Ltd | Hospitality | 2024 |
| Msgj Ltd | Construction | 2024 |
| MSM Mechanical Services Limited | Construction | 2025 |
| MSV Consultancy Services Ltd | Information & communication | 2021 |
| Muhammadiyah AL Quds Ltd | Administrative & support | 2024 |
| Multi-Distribution Limited | Transport & logistics | 1999 |
| Munchbox Club Limited | Hospitality | 2024 |