| Malws Limited | Financial services | 2019 |
| MAN Made Applications Limited | Information & communication | 2022 |
| Mana Mana & Co Limited | Wholesale & retail | 2025 |
| Manor Fields (Freehold) Company Limited | Households | 2006 |
| Manor Fields (Southborough) Management Company Limited | Households | 2004 |
| Manston Construction Ltd | Construction | 2026 |
| Manu Forti Limited | Administrative & support | 2011 |
| MAP Property Management and Letting Ltd | Real estate | 2016 |
| MAP Suppliers Ltd | Wholesale & retail | 2023 |
| Maplecab Ltd | Professional & scientific | 2014 |
| Mapledean Limited | Real estate | 2011 |
| Maplenet Ltd | Information & communication | 2018 |
| Mapleton Homes Limited | Construction | 2003 |
| Mara Mgmt Ltd | Professional & scientific | 2025 |
| Marblellous Ltd | Construction | 2026 |
| MARCH21 Limited | Professional & scientific | 2017 |
| Marden Executive Search Limited | Administrative & support | 2018 |
| Mariusm Services Ltd | Transport & logistics | 2018 |
| Mark Anthony Townsend Carpentry and Building Ltd | Construction | 2014 |
| Mark Gill Design Ltd | Administrative & support | 2008 |
| Mark Kecek Limited | Financial services | 2022 |
| Mark Rasmussen Numismatist Ltd | Wholesale & retail | 2012 |
| Mark Sluimers Treasury Consultancy Limited | Professional & scientific | 2019 |
| Market Town Investments Limited | Real estate | 1981 |
| Marl Partners LLP | | 2012 |
| Marmalade Marketing Ltd | Administrative & support | 2020 |
| Marshall Kenny Limited | Professional & scientific | 2019 |
| Mary Mary Designs Limited | Real estate | 2025 |
| Masquerade Services Ltd | Professional & scientific | 2015 |
| Masterline Communication Strategies Ltd | Professional & scientific | 2025 |
| Matilda Maria Austin Limited | Extraterritorial | 2016 |
| Matjam Ltd | Professional & scientific | 2025 |
| Matlega Construction Limited | Construction | 2007 |
| Matlega Properties Ltd | Construction | 2017 |
| Matrich London Community CIC | Health & social care | 2024 |
| Matrich London Limited | Health & social care | 2020 |
| Mats for Hire Ltd | Administrative & support | 2019 |
| Matt Welch Ltd | Professional & scientific | 2015 |
| Matthews Attractions Limited | Arts & recreation | 2017 |
| Matthews Carousel Ltd | Arts & recreation | 2022 |
| Matthews Events Ltd | Arts & recreation | 2020 |
| Matthews Global Ltd | Arts & recreation | 2023 |
| Matthews Mouse Ltd | Arts & recreation | 2022 |
| MAX Force Trampoline Club Limited | Arts & recreation | 2011 |
| MAX Management & Consultancy Ltd | Professional & scientific | 2024 |
| Maximum Movie Props Ltd | Information & communication | 2017 |
| Maxlen International Limited | Education | 2024 |
| Maxlen Limited | Manufacturing | 2010 |
| Maxwelton Management Limited | Real estate | 2025 |
| MAY Collections Ltd | Administrative & support | 2025 |
| MB Landscaping & Fencing Ltd | Administrative & support | 2025 |
| MB Window Cleaning Services Ltd | Administrative & support | 2019 |
| MBE International Limited | Financial services | 2019 |
| MC Vehicle Repairs Limited | Wholesale & retail | 2018 |
| Mcalister Estates Limited | Hospitality | 1977 |
| MCB Consulting Limited | Professional & scientific | 2017 |
| Mccarthy Surfacing London Limited | Construction | 2003 |
| Mccdh Ltd | Administrative & support | 2022 |
| Mcdonnell Kitchens & Carpentry Ltd | Construction | 2021 |
| Mclaren Information Technology Limited | Information & communication | 2011 |
| Mclean Engineering and Surveying Ltd | Professional & scientific | 2025 |
| Mcvene Limited | Real estate | 2021 |
| MD Autobahn Ltd | Wholesale & retail | 2016 |
| MD Global Limited | Professional & scientific | 2009 |
| Meade Epcs Limited | Professional & scientific | 2025 |
| Meadowtide Ltd | Real estate | 2026 |
| Meadway East Grinstead Limited | Households | 2019 |
| Medialuca Limited | Information & communication | 2025 |
| Meditechnik Limited | Administrative & support | 2004 |
| Meetmypace Ltd | Administrative & support | 2025 |
| Mehmood Developments Ltd | Administrative & support | 2017 |
| MEI Developments Limited | Construction | 2015 |
| MEI Leaf Limited | Extraterritorial | 2018 |
| Melanie Hayward Consultancy Ltd | Professional & scientific | 2019 |
| Melville Mews Management Company Ltd | Households | 2025 |
| Meme Ltd | Wholesale & retail | 2025 |
| Menagerie Interiors Limited | Professional & scientific | 2012 |
| Mengan Limited | Other services | 2003 |
| Meraki IT Recruitment Ltd | Administrative & support | 2026 |
| Meraki Scale Ltd | Professional & scientific | 2024 |
| Mercari Point (London) Ltd | Administrative & support | 2022 |
| Merchant Navy Locomotive Preservation Society Limited | Transport & logistics | 1973 |
| Mercury Power Group Ltd | Construction | 2019 |
| Mercury Power Limited | Construction | 2013 |
| Mereo Ltd | Wholesale & retail | 2014 |
| Meridan-Pro Ltd | Information & communication | 2022 |
| Meridian Properties GB Limited | Real estate | 1995 |
| Merkari Limited | Wholesale & retail | 2025 |
| Merlinbright Construction Limited | Information & communication | 2016 |
| Merron Medical Limited | Health & social care | 2016 |
| Merstham Barber Ltd | Other services | 2022 |
| Merstham Community Facility Trust | Health & social care | 2006 |
| Merstham Glass Limited | Construction | 1977 |
| Merstham Tandoori Ltd | Hospitality | 2024 |
| Messagemaker Displays Limited | Manufacturing | 1999 |
| Messagemaker Limited | Professional & scientific | 1991 |
| Metaecard Limited | Wholesale & retail | 2017 |
| Meyer Enterprises Ltd | Wholesale & retail | 2024 |
| MFP Janson Ltd | Health & social care | 2022 |
| MG Electrical (Surrey) Limited | Construction | 2005 |