| Mckenna Carriage Limited | Transport & logistics | 2019 |
| Mclaren Contracts Limited | Administrative & support | 2004 |
| Mclj Ltd | Professional & scientific | 2025 |
| MCP Creative Production Limited | Administrative & support | 2024 |
| Measure Properties Limited | Real estate | 2018 |
| Mechsell Ltd | Construction | 2015 |
| Mediaflex Rentals Limited | Administrative & support | 2025 |
| Medicam Limited | Manufacturing | 1999 |
| Mediluxe Aesthetics Ltd | Health & social care | 2025 |
| Medin Productions Ltd | Professional & scientific | 2023 |
| Mediskin Aesthetics Ltd | Health & social care | 2019 |
| Melrose Heating and Plumbing Ltd | Construction | 2013 |
| Mentoring Matters Ltd | Professional & scientific | 2020 |
| Meridian Event Services Limited | Administrative & support | 2017 |
| Meridian Financial Partners Limited | Financial services | 2019 |
| Merron and Sons Limited | Construction | 2021 |
| Metropolis Bromley Ltd | Hospitality | 2016 |
| MG Plumbing & Bathroom Services Limited | Construction | 2026 |
| MG Services (UK) Ltd | Construction | 2007 |
| Mgiant 2 Limited | Health & social care | 2025 |
| Mgiant 3 Limited | Health & social care | 2026 |
| MGM New Homes Limited | Construction | 2017 |
| MGS Concrete Pumping Limited | Construction | 2015 |
| Mickleburgh Solutions Limited | Professional & scientific | 2012 |
| Mike West Solutions Ltd | Construction | 2023 |
| Mill Park Developments Limited | Professional & scientific | 2002 |
| Mill Place (Chislehurst) Management Limited | Households | 2004 |
| Milldome Limited | Wholesale & retail | 2000 |
| Mills London Ltd | Administrative & support | 2014 |
| Mills-Meyer Ltd | Wholesale & retail | 2013 |
| Mimos Interiors Ltd | Professional & scientific | 2019 |
| Minlec Electrical Ltd | Construction | 2015 |
| Miop Limited | Information & communication | 1995 |
| Miral Property Ltd | Real estate | 2025 |
| Mirasierra Consulting Limited | Professional & scientific | 2021 |
| Mitchell & Co UK Limited | Real estate | 1997 |
| Mitchell & Mitchell Asset Management Ltd | Financial services | 2022 |
| Mitchell Coaching (London) Limited | Professional & scientific | 2017 |
| Mitchell Lighting Limited | Construction | 2011 |
| Mixoria Limited | Information & communication | 2013 |
| MJC Carpentry and Joinery Ltd | Administrative & support | 2017 |
| MJL Equestrian Limited | Agriculture & fishing | 2015 |
| MK Aesthetics London Ltd | Other services | 2019 |
| MK Aesthetics Training Ltd | Health & social care | 2025 |
| MK Illuminate Ltd | Construction | 2006 |
| MLS Contractors Ltd | Construction | 2012 |
| MLS Group Holdings Ltd | Transport & logistics | 2022 |
| MMJ Farleigh Road Limited | Real estate | 2016 |
| MNC Consulting Ltd | Information & communication | 2011 |
| MNC Technology Limited | Information & communication | 2024 |
| Mobile Hose and Hydraulics Ltd | Manufacturing | 2021 |
| Mode Construction Group Ltd | Construction | 2023 |
| Modular Retaining Walls Ltd | Professional & scientific | 2025 |
| MOK South East Ltd | Construction | 2026 |
| Monger Film Services Ltd | Information & communication | 2021 |
| Monger Properties Ltd | Real estate | 2024 |
| Monohan Avenue 2019 Limited | Real estate | 2019 |
| Monte Assisi Limited | Financial services | 2022 |
| Monument Consultancy Limited | Professional & scientific | 2007 |
| Moorhouse Garage Limited | Wholesale & retail | 2022 |
| Morants Holdings Limited | Professional & scientific | 2005 |
| Morants Promotions Limited | Professional & scientific | 2016 |
| Morrinson & Co Limited | Financial services | 2012 |
| Morrinson Wealth Management LLP | | 2012 |
| Morrinson Wealth Wellbeing Ltd | Administrative & support | 2019 |
| Mosach Property Company Limited | Households | 2024 |
| Motor Werx Ltd | Wholesale & retail | 2010 |
| MP Flying Club Limited | Administrative & support | 2023 |
| MP Metrology Limited | Professional & scientific | 2023 |
| MP Roofing (Kent) Limited | Construction | 2022 |
| MPV London Ltd | Real estate | 2020 |
| MR and MRS Bunting Ltd | Real estate | 2024 |
| MT Property Development Services Ltd | Real estate | 2017 |
| MTR1000 Limited | Professional & scientific | 2002 |
| MTT Event Hire Limited | Other services | 2024 |
| Muchaoutdoors Ltd | Manufacturing | 2019 |
| Mulbarton Court Management Company Limited | Real estate | 2012 |
| Murdock Estate Ltd | Real estate | 2024 |
| Music Integration Services Ltd | Information & communication | 2025 |
| Mvrk Group Ltd | Administrative & support | 2024 |
| Mvrk Ltd | Hospitality | 2020 |
| Mwij Properties Ltd | Real estate | 2025 |
| MWM Stunts Limited | Other services | 2013 |
| Myexecassistant Ltd | Administrative & support | 2022 |
| Myrie.London Limited | Information & communication | 2017 |
| Mzuk Ltd | Professional & scientific | 2011 |
| N. E. W. Sivyer Ltd. | Extraterritorial | 2021 |
| N.P. Prime Ltd | Transport & logistics | 2026 |
| N.P.C. Catering Limited | Hospitality | 2003 |
| N.R.C. Properties Limited | Real estate | 1957 |
| Napoli E Brothers Limited | Hospitality | 2023 |
| Narwhal Sciences Ltd | Professional & scientific | 2012 |
| Naughty Gnome Ltd | Administrative & support | 2003 |
| NCW Management Limited | Arts & recreation | 2026 |
| Neat AV Limited | Information & communication | 2015 |
| Nejen Limited | Professional & scientific | 2023 |
| Nelmma Group Limited | Transport & logistics | 2024 |
| Nelson Direct Marketing Limited | Transport & logistics | 2010 |
| Neltah Health Clinic Ltd | Health & social care | 2021 |
| Neuropsychiatry Reports Ltd | Health & social care | 2017 |