| Mediaconx Ltd | Information & communication | 2018 |
| Medical Workwear Ltd | Wholesale & retail | 2025 |
| Medicare SD Ltd | Education | 2025 |
| Medijourn Global Holdings Ltd | Administrative & support | 2022 |
| Mediq Ltd | Professional & scientific | 2024 |
| Medscred UK Ltd | Professional & scientific | 2025 |
| Medsontrack Limited | Information & communication | 2010 |
| Medstar Supported Living Care Services Limited | Health & social care | 2010 |
| Meemo Consulting Limited | Administrative & support | 2012 |
| Meena Halai Wealth Solutions Limited | Financial services | 2015 |
| Meera Trader Ltd | Wholesale & retail | 2024 |
| Meesha Consulting Limited | Professional & scientific | 2002 |
| Mega Consultancy Limited | Professional & scientific | 2022 |
| Mega Estate Management Ltd | Real estate | 2016 |
| Megaplumb Maintenance Ltd | Construction | 2022 |
| Meghana IT Solutions Ltd | Information & communication | 2014 |
| Meghani Ltd | Construction | 2023 |
| Meha Ltd | Financial services | 2017 |
| Mehdicare for YOU Ltd | Health & social care | 2023 |
| Mehmani Limited | Hospitality | 2019 |
| Mehmood Family Partnership LLP | | 2019 |
| Mehta and Shah Holding Ltd | Real estate | 2024 |
| Mekong Electrical Services Ltd | Construction | 2025 |
| Melanie Fallowfield Limited | Arts & recreation | 2025 |
| Melanie Retail Ltd | Wholesale & retail | 2017 |
| Melclose Limited | Real estate | 2012 |
| Melody Arts Limited | Arts & recreation | 2019 |
| Melody Lauren Music Limited | Information & communication | 1982 |
| Mema Management Accountants Ltd | Professional & scientific | 2018 |
| Memo Express Ltd | Transport & logistics | 2019 |
| Mendme UK Limited | Health & social care | 2017 |
| Meon Agency Limited | Professional & scientific | 2025 |
| MER Solutions Ltd | Construction | 2025 |
| Mera Care Limited | Health & social care | 2026 |
| Merch Stop Ltd | Manufacturing | 2025 |
| Merchandise Holdings Ltd | Wholesale & retail | 2015 |
| Merchant Tech Distribution Ltd | Manufacturing | 2021 |
| Mercury Carbon Limited | Professional & scientific | 2025 |
| Merivale Estates Limited | Real estate | 2015 |
| Merlin Cooling Systems Ltd | Manufacturing | 2018 |
| Merlin Crescent Services Ltd | Information & communication | 2019 |
| Merviq Education Ltd | Education | 2023 |
| Mesateq Ltd | Manufacturing | 2013 |
| Meta Profiling Ltd | Administrative & support | 2012 |
| Metabetter Technologies Limited | Wholesale & retail | 2024 |
| Metalbox PIL Limited | Arts & recreation | 2009 |
| Metro Consultancy Limited | Professional & scientific | 2009 |
| Metrocity Properties Limited | Real estate | 2024 |
| Metropolis Property Investments Ltd | Real estate | 2021 |
| Metropolis Solutions Ltd. | Wholesale & retail | 1996 |
| Mews Property Ltd | Real estate | 2025 |
| MFD Properties Limited | Real estate | 2018 |
| MG Accountancy & Tax Services Limited | Wholesale & retail | 2014 |
| MGM Properties (London) Limited | Real estate | 2012 |
| MGM Qspm Limited | Professional & scientific | 2011 |
| Mgold Limited | Manufacturing | 2015 |
| MH Resonance Limited | Health & social care | 2023 |
| MH Way Trading Limited | Wholesale & retail | 2023 |
| MHX Ltd | Construction | 2025 |
| MI Property Investment Ltd | Households | 2020 |
| Miami Prestige Ltd | Administrative & support | 2017 |
| Mian Ltd | Information & communication | 2014 |
| Miayan Limited | Wholesale & retail | 2019 |
| Micaela Blitz Ltd. | Information & communication | 2014 |
| Michael Dobbs Entertainment Limited | Professional & scientific | 2011 |
| Michael Doran Q.S. Services Limited | Professional & scientific | 2008 |
| Michael King Accountants Limited | Professional & scientific | 2026 |
| Michael Mokawem Medical Practice Limited | Health & social care | 2020 |
| Michelle's Deli Limited | Hospitality | 2014 |
| Micro Smart Ltd | Information & communication | 2006 |
| Mictel Hillpress Limited | Manufacturing | 2013 |
| Midas Consulting Services Ltd. | Information & communication | 2016 |
| Midas Technical Solutions Limited | Information & communication | 1998 |
| Midchange Property Management Limited | Households | 1989 |
| Middle East Ventures Limited | Hospitality | 1999 |
| Middle West Curry Farm Limited | Administrative & support | 2002 |
| Middlesex Association for the Blind(The) | Health & social care | 1952 |
| Middlesex Golf Limited | Arts & recreation | 2017 |
| Middlesex Junior Cricket Academy Limited | Education | 2025 |
| Middlesex Property Investments Limited | Real estate | 2007 |
| Midland Mews RTM Company Limited | Households | 2020 |
| Midx Traders Ltd | Construction | 2025 |
| Mijaki & Co Ltd | Professional & scientific | 2024 |
| Mika Interiors Limited | Construction | 2018 |
| Mikka Appliances UK Limited | Extraterritorial | 2016 |
| Mila Advisory Ltd | Professional & scientific | 2018 |
| Mila Real Estate Limited | Construction | 2017 |
| Milad Investments Ltd | Real estate | 2022 |
| Milebush Properties Limited | Construction | 1963 |
| Milefield Properties Limited | Extraterritorial | 2015 |
| Millarrow Limited | Extraterritorial | 2001 |
| Millennials Art Limited | Wholesale & retail | 2020 |
| Millie Events Limited | Other services | 2024 |
| Millscape Landscaping Ltd | Administrative & support | 2017 |
| Milstar Investments Limited | Real estate | 2018 |
| Milton Healthcare Limited | Professional & scientific | 2011 |
| MIM Marketing Ltd | Extraterritorial | 2025 |
| Mimar Sinan Properties Ltd | Real estate | 2019 |
| Mimiprop Ltd | Real estate | 2025 |
| Mimosa Insights Limited | Professional & scientific | 2025 |