| Mcmullan Associates Limited | Professional & scientific | 2022 |
| MCN Prestige Services Ltd | Construction | 2021 |
| Mcvc Limited | Administrative & support | 2025 |
| MD Engineering Solutions Limited | Construction | 2026 |
| MD Garden Specialists Ltd | Administrative & support | 2024 |
| MD Rail Limited | Construction | 2018 |
| MD Security Limited | Administrative & support | 2014 |
| MD Services the Drivers Solution Ltd | Professional & scientific | 2007 |
| MDA Electrical Limited | Construction | 2015 |
| MDC Food Safety and HSE Solutions Limited | Health & social care | 2014 |
| MDG Plastering & Rendering Services Limited | Construction | 2015 |
| MDM Interiors Limited | Construction | 2015 |
| MDM Structural and Civil Engineering Ltd | Construction | 2017 |
| MDO Consultancy Ltd | Professional & scientific | 2020 |
| MDS Surveying Ltd | Professional & scientific | 2026 |
| MDT Property Services Ltd | Construction | 2022 |
| ME & Co Property Limited | Households | 2019 |
| Meadowsheath Limited | Professional & scientific | 2025 |
| Meatopia (UK) Ltd | Hospitality | 2015 |
| Medalist Estates Ltd | Households | 2024 |
| Medi Rampal Ltd | Energy | 2021 |
| Media Structures Limited | Administrative & support | 1991 |
| Medistra Group Limited | Other services | 2026 |
| Mednetiks Ltd | Professional & scientific | 2020 |
| Megelle Limited | Other services | 2016 |
| Megp Limited | Real estate | 2026 |
| Mehta Brothers (Jetpur) Limited | Real estate | 2010 |
| MEL Kenyon Beauty Ltd | Other services | 2019 |
| Melanin Kitchen Ltd | Health & social care | 2022 |
| Melena Mane Ltd | Other services | 2026 |
| Melhuish Holdings Ltd | Financial services | 2023 |
| Melmeg Limited | Construction | 2018 |
| Melstruct Limited | Professional & scientific | 2023 |
| Memory Business Systems Limited | Wholesale & retail | 1996 |
| MEN Grooming (Sidcup) Ltd | Other services | 2020 |
| Mennekes Electric Limited | Manufacturing | 1987 |
| Meraki Estates Limited | Professional & scientific | 2017 |
| Mercredi Ltd | Information & communication | 2017 |
| Mercy Theatre Collective Community Interest Company | Arts & recreation | 2024 |
| Mereddy Holdings Limited | Real estate | 2019 |
| Meridian Management Consultants Limited | Professional & scientific | 2024 |
| Mermaid Cafe Bar Limited | Hospitality | 2020 |
| Merrill Electrical Limited | Construction | 2018 |
| Merton Court School LLP | | 2009 |
| Mertonian Holdings Limited | Financial services | 2020 |
| MES Contractors Limited | Construction | 2018 |
| Messageroute Ltd | Information & communication | 2009 |
| Mesupportcare Ltd | Health & social care | 2020 |
| Meta Rail Engineering Services Ltd | Professional & scientific | 2026 |
| Metatron Services Ltd | Administrative & support | 2025 |
| Metcraft Finished Products Limited | Administrative & support | 2012 |
| Methodic Productions Ltd | Professional & scientific | 2020 |
| Metricsynapse Ltd | Information & communication | 2026 |
| Metrobar Sidcup Limited | Real estate | 2012 |
| Metropole Properties Limited | Real estate | 2020 |
| Metta Management Limited | Professional & scientific | 2007 |
| MG Elevators Limited | Construction | 2014 |
| MG Renovations Limited | Administrative & support | 2014 |
| MG1 Properties Ltd | Real estate | 2021 |
| Mgtk Limited | Wholesale & retail | 2024 |
| MH Training & Development Solutions Limited | Information & communication | 2002 |
| MHN Educational Consultancy Ltd. | Professional & scientific | 2010 |
| Michael Burrell Limited | Administrative & support | 2015 |
| Michael Daniel (UK) Ltd | Health & social care | 2014 |
| Michael Daniels Limited | Other services | 1989 |
| Michal Flis Ltd | Transport & logistics | 2020 |
| Michalski AV Ltd | Professional & scientific | 2026 |
| Micks Transport Ltd | Transport & logistics | 2021 |
| MID Kent Construction Limited | Other services | 2013 |
| Middletonmurray Infrastructure Services Limited | Construction | 2014 |
| Mihai and SON Limited | Construction | 2016 |
| Mihmic Investments Limited | Real estate | 2017 |
| Mika:Timing UK Ltd | Professional & scientific | 2025 |
| Mikazukido UK Limited | Hospitality | 2024 |
| Milercentral Ltd | Wholesale & retail | 2025 |
| Millcham Ltd | Construction | 2021 |
| Millennia Security Solutions Limited | Administrative & support | 2025 |
| Millionair Magazine Limited | Information & communication | 2023 |
| Milo's Barbers Limited | Other services | 2003 |
| MIN Design Studio Limited | Arts & recreation | 2016 |
| Minasons Properties Ltd | Administrative & support | 2020 |
| Mind Ninja Ltd | Education | 2020 |
| Mindmates Ltd | Wholesale & retail | 2025 |
| Mini PT Ltd | Information & communication | 2021 |
| Mini Tribe Ltd | Health & social care | 2024 |
| Minicucci Ltd | Real estate | 2025 |
| Mintfield Property Management Limited | Professional & scientific | 1983 |
| Mipharm Limited | Health & social care | 2025 |
| Mirchu Estates Limited | Real estate | 2024 |
| Mischicks Beauty Ltd | Other services | 2021 |
| Mischicks Day Spa Ltd | Other services | 2024 |
| Miss Richardson's Dogs Ltd | Other services | 2020 |
| Miss Richardson's House Sitting Ltd | Other services | 2022 |
| Miss Richardson’S Training Ltd | Other services | 2024 |
| Miss YOU Mail Limited | Wholesale & retail | 2025 |
| Missen & Baker Decorating Services Limited | Administrative & support | 2019 |
| Mission Complete Limited | Transport & logistics | 2006 |
| Mitchell Hedges Limited | Administrative & support | 2010 |
| Miti Ltd | Wholesale & retail | 2021 |
| Mizen Shoes & Keys Ltd | Other services | 2026 |