| Mascot Construction Ltd | Construction | 2024 |
| Mason&Hendricks Consulting Ltd | Financial services | 2021 |
| Master Fabrication Service Ltd | Extraterritorial | 2017 |
| Masterclass Roofing and Building Services Ltd | Construction | 2025 |
| Mata LDN Limited | Professional & scientific | 2024 |
| Material Dialogue Limited | Professional & scientific | 2024 |
| Materiality Future Ltd | Professional & scientific | 2025 |
| Maviel Ltd | Financial services | 2022 |
| MAW Construction Limited | Construction | 2022 |
| MAX Zard Publishing Ltd | Wholesale & retail | 2021 |
| Maximum Response Limited | Information & communication | 2017 |
| Maxin Group Limited | Information & communication | 2019 |
| Mayfair-Ew Ltd | Transport & logistics | 2026 |
| Mayo Elec Ltd | Construction | 2014 |
| MB London Consultancy Limited | Professional & scientific | 2019 |
| MB Source Ltd | Information & communication | 2023 |
| Mbtract Ltd | Information & communication | 2025 |
| MC Bars (Inn on the Green) Limited | Hospitality | 2016 |
| MC Bars Limited | Hospitality | 2003 |
| MC Central Logistics Ltd | Administrative & support | 2021 |
| MC London Services Limited | Construction | 2017 |
| MCA Tickets Ltd | Wholesale & retail | 2024 |
| Mccm Properties Limited | Extraterritorial | 2014 |
| Mchn Ltd. | Extraterritorial | 2021 |
| Mcnlink Labs Limited | Information & communication | 2026 |
| Mcqueen Cairns Ltd | Manufacturing | 2024 |
| MDD Legal Ltd | Other services | 2020 |
| Mdonzelli Ltd | Professional & scientific | 2023 |
| ME and Olja Limited | Financial services | 2025 |
| Medallist Ltd | Administrative & support | 2007 |
| Media Academy of Satireology Ltd | Education | 2025 |
| Media Hamster Ltd | Professional & scientific | 2021 |
| Media N Screen Ltd | Hospitality | 2023 |
| Medicines Solutions for Care Limited | Professional & scientific | 2026 |
| Mediphillics Ltd | Wholesale & retail | 2024 |
| Medius Unus Limited | Financial services | 2018 |
| Mega Meal House Ltd | Wholesale & retail | 2025 |
| Megan Double Glazing Limited | Construction | 2026 |
| Megan Glazing Ltd | Construction | 2018 |
| Mehreet Foods Limited | Manufacturing | 2026 |
| Melcolab Ltd | Information & communication | 2023 |
| Melville Wholesale Ltd | Wholesale & retail | 2025 |
| Memory Filming Limited | Information & communication | 2021 |
| Mental (Health) Wealth Matters Ltd | Health & social care | 2022 |
| Mergestic Management Ltd | Wholesale & retail | 2023 |
| Merix Limited | Administrative & support | 1998 |
| Merum Technologies LLP | | 2023 |
| Messier 33 Entertainment Limited | Information & communication | 2019 |
| Metal (K) Trading Ltd | Wholesale & retail | 2015 |
| Metalwash Limited | Wholesale & retail | 1995 |
| Metaverse Accounting Ltd | Extraterritorial | 2021 |
| Meteor Edtech Ltd | Education | 2019 |
| Metta LAB Ltd | Wholesale & retail | 2022 |
| Mezig Ltd | Professional & scientific | 2020 |
| MFI Marketing INT. LLP | | 2021 |
| MFM Contractors Ltd | Construction | 2020 |
| Mhitar Limited | Real estate | 2016 |
| Mhpaire Limited | Professional & scientific | 2019 |
| MI Laser and Aesthetics Limited | Health & social care | 2023 |
| Miami Beauty Limited | Other services | 2016 |
| Michael Richards Property Management Limited | Administrative & support | 2012 |
| Michaelic Health Solutions Ltd | Health & social care | 2024 |
| Midas 360 Ltd | Information & communication | 2018 |
| Midastouch Productions Limited | Information & communication | 2012 |
| Miftari Construction Ltd | Construction | 2014 |
| Migasuto Holdings Ltd | Administrative & support | 2023 |
| Migasuto Services Ltd | Real estate | 2023 |
| Mikbonsai Ltd | Wholesale & retail | 2012 |
| Mike IT Security Services Limited | Information & communication | 2024 |
| Milandon Ltd | Other services | 2024 |
| Milara Ltd | Wholesale & retail | 2024 |
| Millennial Falkon Ltd | Information & communication | 2025 |
| Millennial Films Limited | Arts & recreation | 2018 |
| Millennium Health Supplements Limited | Wholesale & retail | 2004 |
| Millennium Metalwork Ltd | Manufacturing | 2022 |
| Miller Music Management Limited | Arts & recreation | 2008 |
| Milo Hospitality Ltd | Hospitality | 2019 |
| Mimi Capital Limited | Real estate | 2026 |
| Mimi Nails & Hair Limited | Other services | 2014 |
| Mind Bomb Limited | Professional & scientific | 2010 |
| Mind the Creative Limited | Professional & scientific | 2017 |
| Mindhaus Limited | Health & social care | 2000 |
| Mindlinks IT Services Ltd | Information & communication | 2017 |
| Mindoro Developments Ltd | Construction | 2020 |
| Mindqube Limited | Information & communication | 2020 |
| Minds to Media CIC | Information & communication | 2024 |
| Mirame Beauty Ltd | Other services | 2018 |
| Miro Removal Ltd | Transport & logistics | 2026 |
| Misha Associates Ltd | Information & communication | 2017 |
| Mitcorp (UK) Limited | Information & communication | 1993 |
| Mitcorp Broadcast Rental Limited | Wholesale & retail | 1997 |
| Mitcorp Digital Media Limited | Information & communication | 2003 |
| Mitcorp International Limited | Information & communication | 2005 |
| MK Global Recruitment Limited | Construction | 2023 |
| MK Self Love and Care Ltd | Education | 2021 |
| MKS Pharma Ltd | Wholesale & retail | 2025 |
| MM Future Land Ltd | Real estate | 2025 |
| MMB Solutions Limited | Other services | 2021 |
| MMM Apartments Ltd | Hospitality | 2017 |
| MMM Property Ltd | Hospitality | 2017 |