| MAS Heating Systems Limited | Construction | 2002 |
| Masc Print Ltd | Manufacturing | 2010 |
| Mash Aviation Limited | Education | 2023 |
| Masonic Buildings (Rugby) Limited | Other services | 1934 |
| Master Locksmiths Association | Other services | 1986 |
| Master Technical Solutions Ltd. | Administrative & support | 2018 |
| Masterbuild Group Limited | Construction | 2013 |
| MAT - Delivery Ltd | Transport & logistics | 2017 |
| Matal Trans Ltd | Transport & logistics | 2023 |
| MATE2011 Trans Ltd | Transport & logistics | 2018 |
| Matega Limited | Real estate | 2003 |
| Matei Drivers Limited | Transport & logistics | 2018 |
| Matlas Ltd | Wholesale & retail | 2017 |
| Matrix.Fun (UK) Ltd | Information & communication | 2025 |
| Matrushree Limited | Wholesale & retail | 2022 |
| Matt Clarke Mortgage Services Limited | Financial services | 2014 |
| Mattock Engineering Limited | Professional & scientific | 2015 |
| Matts Auto Services Ltd | Wholesale & retail | 2025 |
| Matwatsoncars Ltd | Financial services | 2023 |
| Maverick Goose Ltd | Professional & scientific | 2021 |
| Maverick Moto Design Ltd | Professional & scientific | 2013 |
| MAX Does Media Ltd | Information & communication | 2025 |
| MAX Hand Car Wash Ltd | Administrative & support | 2023 |
| MAX Mobile Detailing Ltd | Other services | 2024 |
| Maxine Gregory Consulting Ltd. | Professional & scientific | 2011 |
| Maxspice Ltd | Real estate | 2009 |
| Maxwells Houses Ltd | Real estate | 2021 |
| MAY Blossom Farm CIC | Agriculture & fishing | 2022 |
| MAY Parsons Consultancy Ltd | Education | 2022 |
| Maya&Lavy Ltd | Other services | 2018 |
| Maybe Enterprises Ltd | Professional & scientific | 2020 |
| Maye Initiatives Ltd | Other services | 2017 |
| MB Uniforms 56 Ltd | Wholesale & retail | 2023 |
| MB Uniforms Ltd | Wholesale & retail | 2016 |
| MBA Consulting Limited | Administrative & support | 2015 |
| Mbdoo Ltd | Real estate | 2026 |
| MBI GL Ltd | Transport & logistics | 2018 |
| Mblh Limited | Other services | 2016 |
| MBM Rahnama Ltd | Real estate | 2025 |
| Mbugua Gitau Ltd | Construction | 2025 |
| MC Estate Agents Limited | Real estate | 2019 |
| Mcbootrans Ltd | Transport & logistics | 2019 |
| Mccolm Cardew Limited | Professional & scientific | 1999 |
| Mcculloch Renovation Ltd | Households | 2012 |
| Mcfeat Science Limited | Professional & scientific | 2013 |
| MCG Entertainment Ltd | Arts & recreation | 2026 |
| MCJ Project Solutions Ltd. | Professional & scientific | 2023 |
| Mckee Property Limited | Real estate | 2017 |
| Mckinlay & Cunliffe Limited | Real estate | 1999 |
| Mclean Laurels Consulting Limited | Professional & scientific | 2014 |
| Mcmillan Alloys Limited | Wholesale & retail | 2013 |
| MD Accommodation Limited | Real estate | 2021 |
| MD Property Supply Limited | Real estate | 2019 |
| MDE Spedition Ltd | Transport & logistics | 2025 |
| Mdhp Limited | Construction | 2014 |
| MDM Solutions Ltd | Transport & logistics | 2025 |
| MDM Wealth Ltd | Financial services | 2018 |
| Mdmb Engineering Ltd. | Professional & scientific | 2013 |
| Mdutools Limited | Information & communication | 2026 |
| MDX Corps Limited | Real estate | 2024 |
| ME Sports Limited | Arts & recreation | 2013 |
| Meden Court Management Company Ltd | Extraterritorial | 2014 |
| Mediamh Ltd | Information & communication | 2021 |
| Medianetuk Ltd. | Information & communication | 2015 |
| Mediashak Limited | Wholesale & retail | 2001 |
| Medical Elite Recruitment and Practice Sales Ltd | Financial services | 2010 |
| Medicine World Limited | Wholesale & retail | 2025 |
| Medsherpa Europe Ltd | Other services | 2024 |
| Medwell Creations Limited | Other services | 2012 |
| Medwell Hyde (Holdings) Limited | Financial services | 2023 |
| Medwell Hyde Limited | Construction | 2010 |
| Medwell Productions Limited | Information & communication | 2011 |
| Medwellings Limited | Real estate | 2023 |
| Medwellings SUB Co Limited | Real estate | 2023 |
| Mehaz Associates Limited | Professional & scientific | 2024 |
| Mehaz Limited | Transport & logistics | 2019 |
| Meikle Bros. Limited | Agriculture & fishing | 1952 |
| Melbros Limited | Wholesale & retail | 1985 |
| Mellow Property Ltd | Real estate | 2025 |
| Mellow Yellow (UK) Services Limited | Administrative & support | 2025 |
| Melnicj Limited | Transport & logistics | 2015 |
| Melsons Skip Hire Ltd | Construction | 2023 |
| Melsons Waste Management Ltd | Water & waste | 2025 |
| Mendel Services Ltd | Transport & logistics | 2018 |
| Menoh Ltd | Public administration | 2019 |
| Mental Health in Business Ltd | Professional & scientific | 2018 |
| Mental Health in Education Ltd | Extraterritorial | 2025 |
| Mentors for Women Limited | Professional & scientific | 2018 |
| MEO Electrical Services Limited | Manufacturing | 2018 |
| Meraki Digital Consulting Ltd | Professional & scientific | 2020 |
| Meraki Education Group Limited | Education | 2023 |
| Merchant Wine Ltd | Wholesale & retail | 2024 |
| Mercian Technology Ltd | Information & communication | 2020 |
| Mercury Material Management Limited | Transport & logistics | 1986 |
| Merfu Trans Ltd | Administrative & support | 2016 |
| Meridan Finance Ltd | Financial services | 2024 |
| Meritorious Ltd | Professional & scientific | 2023 |
| Merricourt Limited | Extraterritorial | 2021 |
| Merris Bros (Farmers) Limited | Agriculture & fishing | 1954 |
| Merrylex Ltd | Health & social care | 2023 |