| MAP UK & International Ltd | Administrative & support | 2021 |
| Maplewood Consulting Limited | Professional & scientific | 2025 |
| Maplewood Residents Management Company Ltd | Households | 2026 |
| Marblerun Technologies Limited | Information & communication | 2007 |
| Margaret Street Freehold Limited | Households | 2019 |
| Marie Carlile Residents Management Company Limited | Households | 2003 |
| Marie Redmond Tuition Ltd | Education | 2012 |
| Maritime Archaeology Sea Trust | Professional & scientific | 2010 |
| Market Penetration Services UK Limited | Professional & scientific | 2004 |
| Marketing Momentum Group Ltd | Professional & scientific | 2023 |
| Marketmate Technologies Ltd | Information & communication | 2026 |
| Marley Lake Limited | Households | 2025 |
| Marlow Fields (Management Company) Ltd | Households | 2025 |
| Marlow House Investments Limited | Construction | 1985 |
| Marlow HR Consultancy Ltd | Professional & scientific | 2014 |
| Marlow Inventories Ltd | Real estate | 2022 |
| Marmaladecat Limited | Professional & scientific | 2018 |
| Marquetry Marketing Services Limited | Real estate | 1994 |
| Martellor PTY Limited | Wholesale & retail | 2023 |
| Masie Global Consultancy Ltd | Professional & scientific | 2016 |
| Masson Paper Limited | Manufacturing | 2019 |
| Mast Heritage Limited | Other services | 2015 |
| Matred Rail Ltd | Professional & scientific | 2015 |
| Matters Group Ltd | Construction | 2016 |
| Maxim Communications Trustees Limited | Administrative & support | 2024 |
| Maxim's DE Paris Casino Limited | Professional & scientific | 1995 |
| Maxim's DE Paris Limited | Professional & scientific | 1995 |
| Maxim's,Limited | Professional & scientific | 1907 |
| Maxsoir Limited | Financial services | 2017 |
| Mayfair Watches Ltd | Wholesale & retail | 2021 |
| Mayflower Wine Ltd | Wholesale & retail | 2021 |
| Mbaa Investments | Professional & scientific | 2021 |
| MC Rail Services Ltd | Manufacturing | 2015 |
| Mccallum Farmer Consultancy Ltd | Professional & scientific | 2025 |
| Mcdonagh Investments Limited | Real estate | 2009 |
| Mcgeough Media Ltd | Professional & scientific | 2024 |
| Mckinley (Elvaston Mews) Limited | Real estate | 2010 |
| MCS Investment Holdings Limited | Financial services | 2025 |
| MDH (Group) Limited | Construction | 2014 |
| MDL Consultancy Services Limited | Professional & scientific | 2011 |
| MDN Property Investments Ltd | Real estate | 2019 |
| Meadow Court (Iver) Management Company Limited | Households | 2021 |
| Meadway Services Limited | Real estate | 1987 |
| MEB Equipment Limited | Wholesale & retail | 1998 |
| Mechafin UK Limited | Manufacturing | 1990 |
| Mediation Rescue Limited | Administrative & support | 2015 |
| Medic Mind Ltd | Education | 2020 |
| Medico Beauty Associates (Beaconsfield) Limited | Health & social care | 2016 |
| Medico Beauty Lounge Limited | Health & social care | 2014 |
| Medico-Legal Partnership Limited | Health & social care | 2000 |
| Medlogical Innovations (UK) Limited | Manufacturing | 2026 |
| Medway Community Estates Limited | Administrative & support | 2004 |
| Medway Fundco Limited | Real estate | 2004 |
| Medway Fundco Two Limited | Real estate | 2008 |
| Mega Union UK Limited | Extraterritorial | 2010 |
| Mega-Pak (2014) Limited | Financial services | 2014 |
| Mela Solutions Limited | Information & communication | 1999 |
| Melba Consulting Ltd | Financial services | 2011 |
| Mellowcroft Consultancy Ltd | Professional & scientific | 2024 |
| Menlo Limited | Professional & scientific | 2012 |
| Menlo Partners LLP | | 2012 |
| Menspire Beaconsfield Limited | Other services | 2021 |
| Meon Hills Management Company Limited | Real estate | 2014 |
| Merivio Limited | Administrative & support | 2025 |
| Merovant Ltd | Transport & logistics | 2026 |
| Merridew Monteith Limited | Professional & scientific | 2025 |
| Metcalfe Metal T/A Metcalfe Limited | Manufacturing | 2017 |
| Metcam LLP | | 2013 |
| Metro Fixings Limited | Wholesale & retail | 2013 |
| Metropolis Lighting Limited | Administrative & support | 1998 |
| Mezzanine Consulting Limited | Information & communication | 2008 |
| MF Equestrian Ltd | Agriculture & fishing | 2013 |
| MFC Legal Consulting Limited | Professional & scientific | 2014 |
| MG Information Management Ltd | Professional & scientific | 2015 |
| MG Winter Sports Limited | Administrative & support | 2022 |
| MH Corp Ltd | Construction | 2009 |
| Michael Property Services Ltd | Real estate | 2024 |
| Michael Shanly Homes Limited | Extraterritorial | 1969 |
| Michaels Properties Ltd | Real estate | 2000 |
| Michelle DE Neys Display and Design Limited | Other services | 2015 |
| Micro Mobility Labs Ltd | Wholesale & retail | 2023 |
| Mikehow.Com Limited | Administrative & support | 2008 |
| Milesromanshopcraft Ltd | Information & communication | 2021 |
| Milestone SO Limited | Construction | 2005 |
| Mill House Secretarial Limited | Administrative & support | 2000 |
| Millbrook Business Park Ltd | Real estate | 2024 |
| Millie & ME Ltd | Professional & scientific | 2025 |
| Milligan Holdings Limited | Professional & scientific | 2010 |
| Milligan Limited | Real estate | 2002 |
| Million Plus Private Finance Limited | Financial services | 2013 |
| Millsome Management Limited | Real estate | 1999 |
| Millwood Contracts Limited | Construction | 2013 |
| Millwood Designer Homes Kent Ltd | Construction | 1992 |
| Millwood Designer Homes Limited | Construction | 1992 |
| Millwood Homes (Southern) Limited | Extraterritorial | 1994 |
| Milton RD (Adderbury) Management Co Ltd | Households | 2016 |
| Minim's Limited | Professional & scientific | 1983 |
| Mira Retail Limited | Wholesale & retail | 2015 |
| Misbourne House (Gerrards Cross) Management Company Limited | Households | 2018 |
| Mishan (Residential) Limited | Real estate | 1994 |