| Mellia Projects Limited | Construction | 2020 |
| Mellia Properties Ltd | Real estate | 2020 |
| Melling & Carless Ltd | Hospitality | 2017 |
| Mellmark Limited | Information & communication | 2026 |
| Melly IT Consulting Limited | Information & communication | 2026 |
| Memcinnes Limited | Professional & scientific | 2023 |
| Memco Labs Ltd | Information & communication | 2026 |
| Memento Medicines UK Limited | Professional & scientific | 2026 |
| Menai Holiday Cottages Limited | Extraterritorial | 2003 |
| Mental Health Associates Limited | Health & social care | 2003 |
| Mercer-Lane Ltd. | Administrative & support | 2017 |
| Merchants Quay Residents Association Limited | Households | 1998 |
| Mercury Project Management Limited | Professional & scientific | 2022 |
| Mercy Samuelson Limited | Wholesale & retail | 2014 |
| Merebank Tower Ltd | Households | 2013 |
| Merefield Court (Bowden) Management Limited | Real estate | 2002 |
| Merge Content Limited | Information & communication | 2023 |
| Mergence Ventures Ltd | Professional & scientific | 2024 |
| Meridian Medical Services Limited | Financial services | 2007 |
| Merit Beauty Ltd. | Wholesale & retail | 2024 |
| Merit Freight Systems UK Limited | Administrative & support | 2022 |
| Merlewood Management (Bowdon) Limited | Households | 1989 |
| Merlin Court Management Company Limited | Administrative & support | 2001 |
| Merridale Management (Hale) Limited | Hospitality | 1979 |
| Mersey House Regeneration LP | | 2011 |
| Mersey Medics Ltd | Health & social care | 2025 |
| Mersey Valley Care Limited | Health & social care | 2018 |
| Merstham Community Cafe CIC | Hospitality | 2017 |
| Merton Connect Group Ltd | Administrative & support | 2025 |
| Merton Connect Ltd | Administrative & support | 2020 |
| Mesmeric Content Limited | Professional & scientific | 2019 |
| Mestrad Holdings Limited | Extraterritorial | 2016 |
| Meta SAS Limited | Administrative & support | 2012 |
| Metal Recycling and Reclamation Limited | Wholesale & retail | 2025 |
| Metalergon Limited | Administrative & support | 2018 |
| Metalmann Ltd | Manufacturing | 2020 |
| Metalmotif Ltd | Manufacturing | 2020 |
| Metaswitch Networks Ltd | Information & communication | 1981 |
| Metavend Limited | Wholesale & retail | 2022 |
| Metcalfe Holdings Limited | Financial services | 2006 |
| Metel Ltd | Professional & scientific | 2012 |
| Meter Labs PVT. Ltd | Information & communication | 2026 |
| Metro Consultants Limited | Real estate | 1985 |
| Metro MRH Limited | Real estate | 1999 |
| Metro MRI Limited | Real estate | 2005 |
| Metro MRM Limited | Real estate | 2006 |
| Metronomix Studios Limited | Information & communication | 2015 |
| Metrovision 2016 Ltd | Information & communication | 2016 |
| Mews Group Limited | Hospitality | 2024 |
| MFF Polka Limited | Wholesale & retail | 2023 |
| MFG Digital Limited | Financial services | 2022 |
| Mfmam Ltd | Health & social care | 2022 |
| MG Futures Limited | Hospitality | 2013 |
| MG GUT Ltd | Health & social care | 2025 |
| MG Imaginarium Thinkitudes Limited | Professional & scientific | 2016 |
| MG Properties (Manchester) Ltd | Real estate | 2022 |
| Mgait Limited | Professional & scientific | 2024 |
| MGB Retail Consulting Limited | Administrative & support | 2016 |
| MGP (Land) Ltd | Construction | 2025 |
| MGR Bewley LLP | | 2007 |
| MGR Southfields LLP | | 2007 |
| MGW Legal Limited | Professional & scientific | 2017 |
| MH Change Associates Ltd | Professional & scientific | 2020 |
| MH Nutra Limited | Professional & scientific | 2024 |
| MHA Wills Limited | Public administration | 2013 |
| MHF Holdings Ltd | Hospitality | 2024 |
| MHH Investments Limited | Real estate | 2022 |
| MHK ALT Investments Limited | Financial services | 2024 |
| MHK3 Investments Limited | Financial services | 2024 |
| MHK3 Properties Limited | Real estate | 2024 |
| Mhns Consulting Limited | Professional & scientific | 2025 |
| Mhofu IT Resourcing Limited | Information & communication | 2020 |
| MHR (Medical Hair Restoration) Clinic Harrogate/Leeds Limited | Health & social care | 2018 |
| MHR (Medical Hair Restoration) Clinic Manchester/Cheshire Limited | Health & social care | 2015 |
| MHR (Medical Hair Restoration) London/Uk Ltd | Extraterritorial | 2021 |
| MHS Capital Limited | Financial services | 2013 |
| MHS Finance Limited | Financial services | 2013 |
| MHS Group (Holdings) Limited | Administrative & support | 2015 |
| MHX Consulting Ltd | Professional & scientific | 2022 |
| Micad Investments Holdings Limited | Professional & scientific | 2014 |
| Micad Systems (U.K.) Limited | Information & communication | 1987 |
| Micallef Developments Ltd | Real estate | 2023 |
| Michael Alexander Legal Services Limited | Professional & scientific | 2024 |
| Michael Armstrong Limited | Professional & scientific | 2006 |
| Michael C. Fina Holdings Limited | Professional & scientific | 2004 |
| Michael C. Fina Worldwide Limited | Extraterritorial | 2012 |
| Michael Cowgill Limited | Information & communication | 1997 |
| Michael Denney (Soil Nutrition) Ltd | Agriculture & fishing | 2008 |
| Michael Ellis Dentistry Ltd | Health & social care | 2022 |
| Michael Houghton Inspections Ltd | Administrative & support | 2009 |
| Michael J Andrews Limited | Professional & scientific | 2007 |
| Michelle White Limited | Professional & scientific | 2024 |
| Micro Homes Ltd | Construction | 2021 |
| Microconsultant Ltd | Health & social care | 2025 |
| Microstar UK Holdco Limited | Professional & scientific | 2021 |
| MID Miller Properties Limited | Real estate | 2021 |
| Midas Capital Ltd | Other services | 2024 |
| Midas CP Ltd | Administrative & support | 2025 |
| Midas Prime Limited | Financial services | 2025 |
| Midas Protocol Limited | Financial services | 2023 |