| Mega City Limited | Real estate | 2019 |
| Mega Intercontinental Cable (UK) Limited | Information & communication | 2009 |
| Mega Management Limited | Administrative & support | 2024 |
| Megaa Bargain Ltd | Wholesale & retail | 2023 |
| Megacorp Group Ltd | Wholesale & retail | 2024 |
| Megi & Art Limited | Administrative & support | 2025 |
| Mehak Designs UK Limited | Wholesale & retail | 2012 |
| Mehak Trading Limited | Extraterritorial | 2013 |
| Mehar Brickwork Ltd | Construction | 2022 |
| Mehar SPV Limited | Real estate | 2024 |
| Mehar UK Investments Ltd | Real estate | 2024 |
| Mehkam Properties Ltd | Real estate | 2023 |
| Mehndi by Sage Ltd | Wholesale & retail | 2025 |
| Mehta's Estates Limited | Real estate | 2024 |
| Mehtaab Design & Build Ltd | Construction | 2025 |
| Mehtot & GSP Limited | Information & communication | 2013 |
| MEI Homes Limited | Real estate | 2022 |
| MEL Trainmeup Ltd | Arts & recreation | 2023 |
| Melanie Services Ltd | Wholesale & retail | 2020 |
| Meliexia Ltd | Information & communication | 2026 |
| Melloul Holdings Limited | Households | 2023 |
| Melon Bags Ltd | Wholesale & retail | 2026 |
| Melton Business Park Limited | Real estate | 2023 |
| Meltwater Health Ltd | Information & communication | 2018 |
| Membership Omgtlc Ltd | Administrative & support | 2024 |
| MEN Square Ltd | Information & communication | 2019 |
| Mendi Homes Ltd | Real estate | 2025 |
| Menopause and Cancer Community Interest Company | Health & social care | 2022 |
| Menorien Ltd | Wholesale & retail | 2025 |
| Mental-Rise Ltd | Health & social care | 2021 |
| MER Research Ltd | Professional & scientific | 2025 |
| Mercus Foods Limited | Hospitality | 2021 |
| Mercy Hair Lounge Ltd | Other services | 2025 |
| Mercy Trading Ltd | Wholesale & retail | 2024 |
| Meridiem Law Ltd | Information & communication | 2021 |
| Merit Accountancy Limited | Professional & scientific | 2013 |
| Merivon UK Ltd | Wholesale & retail | 2025 |
| Mero Healthcare Ltd | Health & social care | 2023 |
| Meshabbek Ltd | Information & communication | 2024 |
| Meta Stackz Digital Ltd | Information & communication | 2025 |
| Metatag Media Ltd | Professional & scientific | 2025 |
| Metavertex Limited | Administrative & support | 2025 |
| Metax Digital Ltd | Information & communication | 2025 |
| Metro Corporation Limited | Professional & scientific | 1997 |
| Metsec Services Limited | Wholesale & retail | 2021 |
| Mextor Limited | Transport & logistics | 2025 |
| MF Family Care Ltd | Health & social care | 2024 |
| MF Future Ltd. | Wholesale & retail | 2025 |
| Mfunguamoyo Corporation Ltd | Information & communication | 2020 |
| MG Lansbury Ltd | Real estate | 2020 |
| Mgco Trading Ltd | Professional & scientific | 2019 |
| MGL Stores Ltd | Wholesale & retail | 2023 |
| MGP Partnership Ltd | Real estate | 2020 |
| Mgprecision Limited | Construction | 2025 |
| MGT TTS Ltd | Wholesale & retail | 2025 |
| MH Accommodations Ltd | Real estate | 2024 |
| Mhassnain Ltd | Wholesale & retail | 2024 |
| Mhelody Care Limited | Health & social care | 2022 |
| MHK Cargo Services Limited | Transport & logistics | 2025 |
| MHP Catering Ltd | Hospitality | 2023 |
| MHS Building Services Limited | Construction | 2019 |
| Mian Sahib Ltd | Wholesale & retail | 2025 |
| Miatronic Ltd | Information & communication | 2016 |
| Miau Digital Design Ltd | Information & communication | 2015 |
| Micapril Medical Ltd | Health & social care | 2009 |
| Micasa Design and Build Limited | Professional & scientific | 2015 |
| Micheal Herbert Construction Ltd | Construction | 2017 |
| Michigan Carpentry Ltd | Construction | 2014 |
| Micro Management Ltd | Professional & scientific | 2024 |
| Microhard Communication Express Ltd | Wholesale & retail | 2001 |
| Midas Living Ltd | Construction | 2011 |
| Middlesex Car Rental Ltd | Administrative & support | 2023 |
| Middlesex Car Repair Limited | Wholesale & retail | 2025 |
| Middlesex Cleaners Limited | Administrative & support | 2026 |
| Middlesex Flowers Limited | Wholesale & retail | 2024 |
| Middlesex Learning Partnership | Education | 2011 |
| Middlesex MOT & Tyres Ltd | Other services | 2015 |
| Middlesex Parking Ltd | Other services | 2010 |
| Middlesex Property Holdings Limited | Real estate | 2026 |
| Middlesex Screed Ltd | Construction | 2023 |
| Middlesex Wheel Alignment Limited | Wholesale & retail | 2025 |
| Middleway Street Food Ltd | Hospitality | 2024 |
| Middx Property Investment Ltd | Real estate | 2021 |
| Middx Real Estate Ltd | Real estate | 2023 |
| Middxstricker CC Ltd | Arts & recreation | 2024 |
| Might BE Something Ltd | Wholesale & retail | 2025 |
| Miglani Builders Limited | Construction | 2015 |
| Miglani Investments Ltd | Real estate | 2024 |
| Mihail 21 Ltd | Professional & scientific | 2024 |
| Miindful Ballers CIC | Education | 2023 |
| Mikara Collections Ltd | Wholesale & retail | 2026 |
| Milanion Advanced Systems Limited | Information & communication | 2020 |
| Milanion Group Ltd | Financial services | 2020 |
| Milanion Industries Ltd | Information & communication | 2025 |
| Milanion International Limited | Information & communication | 2020 |
| Milano Bespoke Ltd | Manufacturing | 2026 |
| Milar Ltd | Real estate | 2026 |
| Milas Candles Ltd | Wholesale & retail | 2025 |
| Miles International Limited | Transport & logistics | 2018 |
| Miles Tyre Fitting Limited | Wholesale & retail | 2025 |