| Marron Electrical Services Ltd | Administrative & support | 2009 |
| Marsden Reinforcement Limited | Construction | 2004 |
| Marshall & Broome Ltd | Administrative & support | 2013 |
| Marta's Vinyard Limited | Wholesale & retail | 2000 |
| Marthandys Limited | Real estate | 2016 |
| Martial Arts Horsham LLP | | 2020 |
| Martin Maile Car Sales Limited | Wholesale & retail | 2011 |
| Martino's Restaurants Limited | Hospitality | 2024 |
| Maskell Recruitment Ltd | Administrative & support | 2024 |
| Maslow Pro Limited | Professional & scientific | 2022 |
| Mastermend Ltd | Other services | 2016 |
| Mathaq Limited | Wholesale & retail | 2025 |
| Matt James Limited | Health & social care | 2016 |
| Matt James PS Ltd | Real estate | 2024 |
| Matthews Business Consulting Ltd | Professional & scientific | 2023 |
| Mavistream Limited | Real estate | 2001 |
| MAX Climate Solutions Ltd | Construction | 2019 |
| Maxine Media Management Ltd | Information & communication | 2025 |
| Maxtommy Installation Limited | Construction | 2025 |
| May's Roofing and Leadworks Ltd | Construction | 2022 |
| Mcasso Music Production Limited | Arts & recreation | 2023 |
| MCB Imaging Services Limited | Information & communication | 2002 |
| MCC Line Logistics Ltd | Transport & logistics | 2022 |
| Mcdonald Plumbing Services Limited | Construction | 2025 |
| Mcmahon Electrical Services Limited | Construction | 2018 |
| Md&Co Limited | Construction | 2011 |
| Mdgrecruitment Ltd | Administrative & support | 2025 |
| ME Property Hire Limited | Real estate | 2021 |
| Me&L Build Ltd | Construction | 2025 |
| MED Hospitality Limited | Hospitality | 2025 |
| Medi Saver Limited | Wholesale & retail | 2024 |
| Media Control Environmental Limited | Construction | 2023 |
| Media Control Limited | Construction | 1991 |
| Media Control Management Limited | Energy | 2005 |
| Medimpact Ltd | Wholesale & retail | 2024 |
| Medishare DSP Ltd | Wholesale & retail | 2025 |
| Medishare HS Ltd | Financial services | 2020 |
| Medivex Ltd | Manufacturing | 2025 |
| Medpro Healthcare Limited | Wholesale & retail | 2013 |
| Medua Bilingual Nursery Ltd | Education | 2014 |
| Meerani Limited | Real estate | 2010 |
| Megabite Media Productions Ltd | Information & communication | 2025 |
| Meladi MAA Limited | Financial services | 2017 |
| Melaugh Property Management Ltd | Real estate | 2025 |
| Meltel Homes Ltd | Real estate | 2020 |
| Meltel Housing Ltd | Real estate | 2020 |
| Menace Vintage Ltd | Wholesale & retail | 2020 |
| Mepm Consulting Ltd | Construction | 2022 |
| Mera Investments Ltd | Construction | 2021 |
| Meranti Construction Limited | Construction | 2025 |
| Merchant of London Limited | Wholesale & retail | 2002 |
| Mercury Communications Limited | Professional & scientific | 2011 |
| Merritt Robinson Limited | Wholesale & retail | 2012 |
| Merton Court Management Limited | Households | 1991 |
| Meta Group Construction Ltd | Construction | 2023 |
| Metalk Limited | Professional & scientific | 2013 |
| Metalk Therapy Limited | Professional & scientific | 2026 |
| Metercube Engineering Limited | Construction | 2019 |
| Metway.Comms Limited | Information & communication | 2003 |
| Metz Events Limited | Administrative & support | 2023 |
| MF Care and Housing Recruitment Limited | Hospitality | 2019 |
| MG Capital Funding Ltd | Financial services | 2021 |
| MGS Tennis Ltd | Arts & recreation | 2023 |
| MH Clinops Consultancy Limited | Professional & scientific | 2012 |
| MH International Ltd | Real estate | 2007 |
| MHC Plumbing Ltd | Construction | 2017 |
| MHH Investments Portfolio Ltd | Real estate | 2024 |
| Michelle Marnham Limited | Professional & scientific | 2020 |
| Micron Sales & Services Limited | Professional & scientific | 2001 |
| MID City Holdings Ltd | Construction | 2016 |
| Milan Capital Investments Ltd | Real estate | 2025 |
| Milestone Masonry Group Limited | Construction | 2019 |
| Mill Meadow Farm Ltd | Real estate | 2025 |
| Minerva & Daughters Ltd | Professional & scientific | 2026 |
| Miskin Developments Limited | Construction | 2020 |
| Mitnor Limited | Real estate | 1988 |
| MJ Eatss Limited | Hospitality | 2022 |
| MJD Precision Engineering Limited | Manufacturing | 2003 |
| MKS Building Services Limited | Manufacturing | 2021 |
| MLA Finance Limited | Professional & scientific | 2024 |
| MM Gold Star Ltd | Health & social care | 2016 |
| MM Heating Services Ltd | Construction | 2024 |
| MM Tooth Star Ltd | Health & social care | 2026 |
| MME Loft Conversions Ltd | Construction | 2017 |
| Mmfc Properties Limited | Real estate | 2003 |
| MN & JC Developments Limited | Construction | 2013 |
| Model a Revival Company Ltd | Wholesale & retail | 2020 |
| Model Resolve Limited | Information & communication | 2019 |
| Mokshaco Limited | Other services | 2018 |
| Momentum Search Limited | Administrative & support | 2009 |
| Montague Court (Sidcup) Management Limited | Households | 1986 |
| Montagus Sushi Bar Ltd | Hospitality | 2021 |
| Moodglimmers Ltd | Health & social care | 2024 |
| Moonewood Limited | Construction | 2020 |
| Moorcroft Limited | Households | 1981 |
| Moorefields Consulting Limited | Information & communication | 2011 |
| Moorlands Management Holdings Ltd | Households | 2026 |
| Moorside RD Ltd | Real estate | 2019 |
| Moovery for Home Ltd | Extraterritorial | 2022 |
| Moovery Ltd | Transport & logistics | 2020 |