| MAN and Machine Limited | Wholesale & retail | 1989 |
| Manuka Investments Ltd | Real estate | 2024 |
| Marble MOG Limited | Real estate | 2016 |
| Marcom Design Limited | Information & communication | 2007 |
| Maria Hall Consulting Limited | Professional & scientific | 2016 |
| Marie Mills Management Ltd | Professional & scientific | 2023 |
| Mark Dowthwaite Building Services Ltd. | Construction | 2016 |
| Mark Hewitson Photography Ltd | Professional & scientific | 2016 |
| Marrs Estates Limited | Real estate | 2017 |
| Marson Smith Consulting Ltd | Professional & scientific | 2023 |
| Marsters Associates Limited | Information & communication | 2015 |
| Martin Clarke Media Limited | Administrative & support | 2010 |
| Martyn Haworth Coaching Limited | Professional & scientific | 2011 |
| Mary ANN Edwards & Co. Limited | Professional & scientific | 2012 |
| Mass Groundworks Ltd | Construction | 2024 |
| Matt Partridge Ltd | Extraterritorial | 2018 |
| Matt Plummer VFX Limited | Information & communication | 2024 |
| Matt Slegg Hair Ltd | Other services | 2022 |
| Maven Wireless Ltd | Information & communication | 2024 |
| Mavin & Co Ltd | Administrative & support | 2011 |
| Maxas Eco Plumbing and Heating Limited | Construction | 2016 |
| Maximising Event Revenue Limited | Professional & scientific | 2008 |
| Maximus (Roma) Limited | Other services | 2008 |
| Maze Hair Limited | Other services | 2014 |
| MB Construction and Carpentry Ltd | Manufacturing | 2012 |
| MBL Consultant Engineers Limited | Professional & scientific | 2014 |
| Mbns Limited | Health & social care | 2003 |
| Mcal Management Limited | Transport & logistics | 2018 |
| Mcc+R&D Consulting Limited | Professional & scientific | 2009 |
| Mcclure Holdings Limited | Financial services | 2002 |
| Mcdc Productions Limited | Arts & recreation | 2016 |
| Mcintosh Consulting Ltd | Professional & scientific | 2023 |
| Mcintosh Industries Ltd | Manufacturing | 2012 |
| MDP Woodworking Ltd | Manufacturing | 2026 |
| MDT Trim Ltd | Manufacturing | 2024 |
| Media Ace Limited | Manufacturing | 2010 |
| Medialane International Limited | Information & communication | 2000 |
| Mendes Facilites Management Limited | Administrative & support | 2025 |
| Menerbes and Prestbury Properties Services Limited | Real estate | 1996 |
| Menerbes Properties (Provence) Limited | Real estate | 2013 |
| Mercury Innovation Ltd | Professional & scientific | 2011 |
| Merlin Supply Chain Services Ltd | Administrative & support | 2022 |
| Mervelles Ltd | Professional & scientific | 2018 |
| Meta Cannect Limited | Information & communication | 2014 |
| MGR Foamtex Limited | Manufacturing | 1987 |
| MGR Holdings Limited | Financial services | 1988 |
| MHC Car Sales Limited | Wholesale & retail | 2014 |
| Michael Marczewski Ltd | Information & communication | 2021 |
| MID Bucks Machine Tools Limited | Wholesale & retail | 2000 |
| Mideum Ltd | Information & communication | 2020 |
| Miguel DE Almeida Design Ltd | Professional & scientific | 2022 |
| Mike Zulu Ltd | Arts & recreation | 2024 |
| Miles Takes Limited | Professional & scientific | 2017 |
| Military and Aerospace Coatings (Sales) Limited | Wholesale & retail | 2015 |
| Miller From Sweden Limited | Wholesale & retail | 1978 |
| Milo Targett Ltd | Professional & scientific | 2020 |
| Mind Body & Business Ltd | Professional & scientific | 2019 |
| Mindful Travel Club Ltd | Professional & scientific | 2025 |
| Mindshare Transport Ltd | Transport & logistics | 2018 |
| Minna Design Limited | Wholesale & retail | 2020 |
| Minno Ltd | Professional & scientific | 2017 |
| Mint Office Limited | Wholesale & retail | 2014 |
| Minze Holdings Limited | Administrative & support | 2017 |
| Mirabelle Holdings Limited | Financial services | 2024 |
| Misean Ltd | Information & communication | 2006 |
| Mixergy Limited | Professional & scientific | 2014 |
| MJC Electrical & Security Services Limited | Construction | 2008 |
| MK Gardening Services Ltd | Professional & scientific | 2020 |
| Mobitronix Limited | Information & communication | 2014 |
| Mode Labs Ltd | Manufacturing | 2023 |
| Modern Projects Ltd | Administrative & support | 2014 |
| Monke Ltd | Information & communication | 2020 |
| Moogies Limited | Hospitality | 2013 |
| Moorend Lane Farm Ltd | Extraterritorial | 2015 |
| Moorend Lane Ltd | Agriculture & fishing | 2004 |
| More Onion Ltd | Information & communication | 2014 |
| Moreton Builders LLP | | 2010 |
| Morgan and Associates Limited | Real estate | 2006 |
| MOS Botanicals Limited | Arts & recreation | 2020 |
| Moth Collective Ltd | Information & communication | 2015 |
| Moth Films Ltd | Extraterritorial | 2017 |
| Motorhouse Car Sales Limited | Wholesale & retail | 2024 |
| Mountain High Energy Ltd | Information & communication | 2021 |
| Moving Objects Ltd | Professional & scientific | 2021 |
| Movingportal Ltd | Other services | 2017 |
| MP & Sons Limited | Wholesale & retail | 2007 |
| MP Groundworks & Construction Limited | Construction | 2023 |
| MP Sports Academy Limited | Arts & recreation | 2009 |
| MP Sports Cricket Academy Limited | Education | 2020 |
| MP Sports Development Trust | Other services | 2012 |
| MP Tammo Installs Ltd | Construction | 2017 |
| MPB Oxford Limited | Real estate | 2017 |
| MPM Engineering and Manufacturing Solutions Ltd | Professional & scientific | 2020 |
| Mprp Health Ltd | Health & social care | 2019 |
| MR Mend Shoe Repairs Ltd | Other services | 2012 |
| Mrgb Property Limited | Real estate | 2021 |
| MTM Flooring Solutions Limited | Construction | 2022 |
| Multiplant Holdings Limited | Financial services | 2021 |
| Mummy Loves Limited | Wholesale & retail | 2016 |
| Murchison-Hume Ltd | Manufacturing | 2026 |