| Merrywood Apartments (Thames Ditton) Management Company Ltd | Households | 2023 |
| Meschede Ltd | Information & communication | 2014 |
| Messiah Trading Limited | Other services | 2015 |
| Meta Design Office Limited | Professional & scientific | 2025 |
| Meta Thinking School Ltd | Professional & scientific | 2023 |
| Meta-Twenty Ltd | Arts & recreation | 2020 |
| Metametric Engineering Limited | Construction | 2022 |
| Metametric Overseas Limited | Manufacturing | 2024 |
| Metatech Consultancy Ltd | Professional & scientific | 2022 |
| Methodworx Ltd | Information & communication | 2009 |
| Metis Boost Ltd | Professional & scientific | 2026 |
| Metrolink Ratp DEV Limited | Transport & logistics | 2005 |
| Metropolis London Music Limited | Information & communication | 2011 |
| Metson Limited | Manufacturing | 2006 |
| Mezza Express Ltd | Hospitality | 2026 |
| MF Design Studio Limited | Professional & scientific | 2015 |
| Mgenious Consulting Limited | Information & communication | 2011 |
| Mgenious Solutions Ltd | Information & communication | 2020 |
| MGM Delivery Ltd | Transport & logistics | 2021 |
| MGM Property and Developments Ltd | Construction | 2024 |
| MH Electrical Services (South East) Limited | Construction | 2020 |
| MH Hair Partner Ltd | Other services | 2026 |
| MH Mechigian Ltd | Professional & scientific | 2021 |
| Mhsc Ltd | Health & social care | 2011 |
| Mhtc Limited | Professional & scientific | 2002 |
| Miac (UK) Limited | Professional & scientific | 2009 |
| Miaim Limited | Construction | 1975 |
| Michael Reeves Ltd | Wholesale & retail | 2014 |
| Michael Swiers Limited | Professional & scientific | 2003 |
| Michael Tomkins Limited | Hospitality | 2021 |
| Michelle Hart Hair Ltd | Other services | 2015 |
| Micro Precision Ltd | Professional & scientific | 2023 |
| Microvisk Limited | Manufacturing | 2016 |
| Microvisk Technologies Ltd | Financial services | 2016 |
| MID America (UK) Limited | Wholesale & retail | 1990 |
| Midas Publications Limited | Information & communication | 2002 |
| Middleton CS Ltd | Other services | 2018 |
| Midnexus Limited | Financial services | 2021 |
| MIF Group Holdings Ltd | Financial services | 2020 |
| Mike Silva Ltd | Administrative & support | 2017 |
| Miko Investments Ltd | Real estate | 2024 |
| Milberry Green Glamping Limited | Hospitality | 2022 |
| Milematic Limited | Wholesale & retail | 1991 |
| Militiacc Limited | Transport & logistics | 2019 |
| Miller & Stephens Consultancy Ltd | Professional & scientific | 2023 |
| Millerbird Ltd | Wholesale & retail | 2023 |
| Millmead Trading Limited | Hospitality | 2020 |
| Millson Properties Ltd | Real estate | 2021 |
| Millstream Garage Ltd | Wholesale & retail | 2023 |
| Milner Investment Holdings Ltd | Transport & logistics | 2024 |
| Milton Close Residents' Association Limited | Households | 2006 |
| Mind and Money Matters Ltd | Health & social care | 2023 |
| Mind Games Film Ltd | Information & communication | 2024 |
| Ming Muay Thai Ltd | Arts & recreation | 2025 |
| Mini Crash Club Ltd | Arts & recreation | 2026 |
| Mining Plus UK Limited | Mining & quarrying | 2018 |
| Mint Garden Construction Ltd | Administrative & support | 2016 |
| Mint Spaces Ltd | Administrative & support | 2019 |
| Miotal Limited | Financial services | 2024 |
| Miracle Leaf Wellness Limited | Wholesale & retail | 2019 |
| Miraclean (UK) Ltd | Administrative & support | 2016 |
| Mirakal Services Ltd | Administrative & support | 2015 |
| Mirantis UK Ltd | Information & communication | 2019 |
| Mishary Ltd | Wholesale & retail | 2024 |
| Miss Twickenham Ltd | Wholesale & retail | 2020 |
| Mission Focus Ltd | Professional & scientific | 2020 |
| Mission Ventures Ltd | Administrative & support | 2014 |
| Mistcity Ltd | Wholesale & retail | 2023 |
| Mizon Limited | Information & communication | 2021 |
| MJ UK Accountancy Ltd | Professional & scientific | 2017 |
| MJC Automobile Services Limited | Wholesale & retail | 2003 |
| MJC Limited | Professional & scientific | 2017 |
| Mjdigital Limited | Information & communication | 2013 |
| Mjjg Property Ltd | Real estate | 2025 |
| MJL Construction Mallorca Ltd | Professional & scientific | 2022 |
| MK Brand & Insight Ltd | Professional & scientific | 2018 |
| MK General Building Ltd | Construction | 2023 |
| MK Varda Ltd | Professional & scientific | 2026 |
| Mkac Properties Limited | Real estate | 2021 |
| MKM Facilities Ltd | Construction | 2026 |
| MKZ Limited | Professional & scientific | 2003 |
| ML2000 Limited | Other services | 2019 |
| Mlwb Ltd | Other services | 2022 |
| MM and Co Roofing Limited | Construction | 2023 |
| Mmac Holdings Ltd | Public administration | 2025 |
| MMH Developments Limited | Construction | 2005 |
| MMM Commerce Limited | Wholesale & retail | 2020 |
| Mmrg Limited | Professional & scientific | 2012 |
| MN Product Ltd | Wholesale & retail | 2025 |
| MN Sands Limited | Professional & scientific | 2009 |
| MN Specialists Services Limited | Health & social care | 2016 |
| Mnara Health Ltd. | Health & social care | 2015 |
| Mnlane Investments (2025) Limited | Financial services | 2025 |
| Mobile Business Solutions Ltd | Information & communication | 2007 |
| Mobile Master London Ltd | Wholesale & retail | 2019 |
| Mobilesquared Limited | Professional & scientific | 2013 |
| Mobintec Ltd | Information & communication | 2002 |
| Mode Energy Ltd | Real estate | 2024 |
| Mode Modular Limited | Construction | 2020 |
| Model Property Solutions Ltd | Financial services | 2018 |