| Maytrade Retail and Ecommerce Ltd | Wholesale & retail | 2017 |
| MB Engineering (South East) Limited | Manufacturing | 2010 |
| MB Propco Ltd | Real estate | 2025 |
| MB Superbikes Limited | Wholesale & retail | 2020 |
| MBA Field Marketing Limited | Administrative & support | 2002 |
| Mcardle Made Ltd | Administrative & support | 2025 |
| Mccarthy Electrical Installations Limited | Wholesale & retail | 1960 |
| Mcgovern Properties Limited | Real estate | 2016 |
| Mckenny Consulting Limited | Professional & scientific | 2026 |
| MCL Golf Limited | Wholesale & retail | 2009 |
| Mcmanus Plant Division Limited | Other services | 2024 |
| Mcmanus Projects and Developments Limited | Construction | 2015 |
| Mcmanus Projects Holdings Limited | Financial services | 2024 |
| Mcmanus Property Division Limited | Real estate | 2020 |
| Mcmanus Proprietary Holdings Limited | Financial services | 2020 |
| Mcrae and Soden Limited | Wholesale & retail | 2025 |
| Mcyaffie Associates Ltd | Administrative & support | 2021 |
| MD Ecomm Limited | Wholesale & retail | 2024 |
| MD Fire Doors Ltd | Public administration | 2022 |
| MD Musiclab Ltd | Education | 2022 |
| Meades Meadow Management Company Limited(The) | Households | 1968 |
| Meadow Way Management Ltd | Real estate | 2019 |
| Meat Masters Grocery Limited | Wholesale & retail | 2025 |
| Mechinmotion Ltd | Professional & scientific | 2024 |
| Medical Billing Direct Limited | Administrative & support | 2014 |
| Medical Warehouse Global Ltd | Wholesale & retail | 2011 |
| Medicamento Ltd | Professional & scientific | 2020 |
| Medset Ltd | Education | 2015 |
| Medstone Ltd | Wholesale & retail | 2021 |
| Mega Fabrications Group Ltd | Construction | 2012 |
| Mega Glass Limited | Manufacturing | 2012 |
| Mega Marble Limited | Manufacturing | 1996 |
| Menu 11 Limited | Hospitality | 2021 |
| Merchmerlin UK Limited | Professional & scientific | 2024 |
| Mern Limited | Real estate | 2017 |
| Merriborn Media Ltd | Information & communication | 2001 |
| Metal Creation Limited | Professional & scientific | 2016 |
| Metrisai Ltd | Information & communication | 2025 |
| Metro Cars London Ltd. | Wholesale & retail | 2012 |
| Metsuda Group Ltd | Wholesale & retail | 2019 |
| Metsuda Ventures Ltd | Wholesale & retail | 2023 |
| Mexus Trading Ltd | Wholesale & retail | 2015 |
| MFL in Action Ltd | Professional & scientific | 2024 |
| Mflsurvival Limited | Other services | 2019 |
| MH Properties South East Limited | Real estate | 2023 |
| Mhaadbussiness Limited | Construction | 2025 |
| Mhse Prop Limited | Real estate | 2024 |
| Mi-Signalling Limited | Professional & scientific | 2024 |
| MIA Export Demand Ltd | Administrative & support | 2020 |
| MIA Properties & Estates Ltd | Real estate | 2018 |
| Miaglen Limited | Construction | 1974 |
| Michael Brown Training Limited | Education | 2014 |
| Michelle Elizabeth Limited | Other services | 2018 |
| Middleton Mann Ltd | Information & communication | 2020 |
| Mika Construction Ltd | Construction | 2021 |
| Mikail Trading Ltd | Wholesale & retail | 2024 |
| Mile High Constructions Limited | Construction | 2019 |
| Miles Smith Electrical Ltd | Construction | 2016 |
| Miller & Co Consulting Limited | Administrative & support | 2025 |
| Milleya Plus Ltd | Professional & scientific | 2025 |
| Millgrange Developments Limited | Construction | 2008 |
| Milvus Management Ltd | Professional & scientific | 2019 |
| Mind Therapy Practice Ltd | Health & social care | 2026 |
| Minding the GAP Education CIC | Hospitality | 2022 |
| Mindlit Consultancy Limited | Professional & scientific | 2026 |
| Mindlit Limited | Financial services | 2026 |
| Mintu Cargo Ltd | Transport & logistics | 2025 |
| Mirant Limited | Information & communication | 2019 |
| Misbourne Environmental Protection Limited | Professional & scientific | 2021 |
| Miss Neud UK Ltd | Wholesale & retail | 2021 |
| Mitti Engineering Services Limited | Administrative & support | 2014 |
| MJ Mall Limited | Wholesale & retail | 2025 |
| MJ Yerrell Ltd | Construction | 2002 |
| MJC Electrical & Fire Services Limited | Construction | 2019 |
| Mjchard Mobile Commercial Repairs Limited | Professional & scientific | 2019 |
| MJS1 Limited | Construction | 2017 |
| MLK Consulting Ltd | Professional & scientific | 2026 |
| Mlosec Ltd | Health & social care | 2013 |
| MM Living Solutions Ltd | Real estate | 2024 |
| MM People Change & Transformation Ltd | Professional & scientific | 2024 |
| MM Property Repair Services Limited | Construction | 2020 |
| MM Rheumatology Ltd | Health & social care | 2021 |
| MNC CRM Consulting Limited | Information & communication | 2017 |
| MNS Cherry Tree Ltd | Hospitality | 2025 |
| Mnsk Holdings Limited | Information & communication | 2025 |
| Mobicloud Limited | Professional & scientific | 2012 |
| Mobile Tyres Specialists Co Ltd | Wholesale & retail | 2021 |
| Modiform UK Ltd | Administrative & support | 2005 |
| Moena Ltd | Health & social care | 2021 |
| Momentum Safety Specialists Limited | Professional & scientific | 2007 |
| Monastery of Sound Ltd. | Information & communication | 2003 |
| Money Boxed Ltd | Professional & scientific | 2023 |
| Monster Phonics Ltd | Education | 2015 |
| Moomeg Limited | Construction | 2014 |
| Moonag Limited | Information & communication | 2012 |
| Morsun Properties Limited | Real estate | 2013 |
| Mosaic PM Ltd | Professional & scientific | 2025 |
| Mossform Limited | Professional & scientific | 1988 |
| Most Well Ltd | Hospitality | 2018 |
| MOT Plus Limited | Wholesale & retail | 2014 |