| Metal Rainwater Solutions Ltd | Construction | 2021 |
| Metaledge Solutions Ltd | Manufacturing | 2026 |
| Metalink Foundation | Financial services | 2025 |
| Metallicity Ltd | Professional & scientific | 2023 |
| Metals Research Limited | Manufacturing | 1997 |
| Metametrics Lexile UK Ltd | Extraterritorial | 2024 |
| Metanate Limited | Information & communication | 2000 |
| Metaopikchu Ltd | Manufacturing | 2025 |
| Metaphora Studios Limited | Information & communication | 2021 |
| Metastack Solutions Ltd. | Extraterritorial | 2005 |
| Metertutor Ltd | Education | 2025 |
| Method 2.0 Limited | Administrative & support | 2019 |
| Methuselah Health UK Limited | Professional & scientific | 2014 |
| Meticuly Innovations Ltd | Manufacturing | 2021 |
| Metis Reasoning Ltd | Information & communication | 2026 |
| Metison Limited | Professional & scientific | 2017 |
| Metisox Limited | Professional & scientific | 2014 |
| Metrion Biosciences Ltd | Professional & scientific | 2015 |
| Metrion Pharma Ltd | Professional & scientific | 2018 |
| Metro Print Management Ltd | Manufacturing | 2004 |
| Metropolitan Imports and Distribution Ltd. | Wholesale & retail | 2015 |
| Mettas Intl Import and Export Co., Ltd | Wholesale & retail | 2025 |
| Mettingham Technology Limited | Administrative & support | 2013 |
| Mexuk Ltd. | Hospitality | 2023 |
| Mezolen Industry Co., Ltd. | Financial services | 2013 |
| MFN Projects Ltd | Construction | 2026 |
| MFY Global Holdings Ltd | Information & communication | 2024 |
| MFY Holdings Ltd | Information & communication | 2024 |
| MG Aircraft Ltd | Manufacturing | 2025 |
| MG Care Ltd | Health & social care | 2025 |
| MG Property Lets Ltd | Real estate | 2022 |
| MG Site Fabrications Limited | Construction | 2001 |
| MG Steel Erection & Site Welding Ltd | Extraterritorial | 2024 |
| Mgang Ltd | Wholesale & retail | 2025 |
| MGL Maltings Ltd | Hospitality | 2020 |
| MGN Aviation Support Ltd | Manufacturing | 2025 |
| MGN Healthcare Ltd | Administrative & support | 2023 |
| Mgna Jaani Ltd | Hospitality | 2019 |
| Mgng Ltd | Information & communication | 2024 |
| Mgph Limited | Construction | 1978 |
| MGT Support | Health & social care | 2024 |
| MH Activewear Ltd | Wholesale & retail | 2024 |
| MHC Maritime Technology Service Co., Ltd | Wholesale & retail | 2024 |
| Mhmb Taverns Ltd | Hospitality | 2023 |
| MHT Partners LLP | | 2011 |
| MI Homes Developments Limited | Construction | 2017 |
| MIA IP Limited | Administrative & support | 2022 |
| MIB Security Services UK Ltd | Administrative & support | 2011 |
| MIC Investment Management Ltd | Real estate | 2022 |
| MIC Sports Co., Ltd | Wholesale & retail | 2023 |
| Micarufa Ltd | Extraterritorial | 2016 |
| Michael Balcon Productions Ltd | Information & communication | 2021 |
| Michael Beaumont Butchers (Linton) Ltd | Wholesale & retail | 2016 |
| Michael Caine Motorsport Ltd. | Wholesale & retail | 2006 |
| Michael Lewis Audit Limited | Professional & scientific | 2002 |
| Michael Lewis Limited | Professional & scientific | 1996 |
| Michael Lewis Partners Limited | Professional & scientific | 2013 |
| Michael Scott Associates Limited | Construction | 2005 |
| Michael Sheppard & Co Ltd | Information & communication | 1986 |
| Michael Taylor Ltd | Professional & scientific | 2021 |
| Michael Williams Engineering Limited | Manufacturing | 1992 |
| Michael Yelland Associates Limited | Administrative & support | 2003 |
| Michael's Shoes Limited | Other services | 2011 |
| Michal Maszkiewicz Limited | Information & communication | 2014 |
| Michelle Reed Ltd | Hospitality | 2013 |
| Michos Salad Bar Limited | Hospitality | 2019 |
| Michugbo Ltd | Health & social care | 2023 |
| Mick Davies Education Limited | Education | 2013 |
| Microbial Technics Limited | Professional & scientific | 1994 |
| Microbiotica Limited | Professional & scientific | 2016 |
| Microcoins Limited | Financial services | 2023 |
| Microgravity Bioreactors Ltd | Professional & scientific | 2025 |
| Microinti Limited | Information & communication | 2010 |
| Microphantoms Ltd | Professional & scientific | 2023 |
| Micropraxis Ltd | Information & communication | 2001 |
| Microsens Diagnostics Limited | Extraterritorial | 2013 |
| Microsensdx Limited | Manufacturing | 1999 |
| Microsoft Research Limited | Information & communication | 1997 |
| Microsurgery Training Ltd | Education | 2020 |
| Microwire Limited | Professional & scientific | 2006 |
| Mics Composites Ltd | Manufacturing | 2018 |
| MID Century Millie Limited | Wholesale & retail | 2021 |
| Midas Blue Limited | Professional & scientific | 2003 |
| Midas Green Limited | Financial services | 2002 |
| Midas Yellow Limited | Information & communication | 2003 |
| Middle Watch (Residents Association) Limited | Households | 1997 |
| Middleton Close (Cambridge) Management Company Limited | Households | 2014 |
| Midland Press Ltd | Manufacturing | 1988 |
| Midland Robotics Ltd | Manufacturing | 2019 |
| Midrago Ltd | Manufacturing | 2025 |
| Midsummer Estates Limited | Real estate | 1983 |
| Midsummer Holdings Limited | Construction | 1986 |
| Midsummer House Restaurants LLP | | 2011 |
| Midsummer Meadows Limited | Real estate | 1986 |
| Midsummer Models Limited | Administrative & support | 2007 |
| Midsummer Place (Cambridge) Property Management Company Limited | Administrative & support | 2016 |
| Midsummer Securities Limited | Construction | 1982 |
| Midsummer Wealth Ltd | Financial services | 2025 |
| Midts Limited | Information & communication | 2013 |
| Miefoame Ltd | Manufacturing | 2025 |