| MJB Trading Ltd | Construction | 2020 |
| MJK Powder Coating Services Ltd | Construction | 2020 |
| MJN Project Management Limited | Administrative & support | 2005 |
| MK Collective Limited | Health & social care | 2026 |
| MK Insight & Data Ltd | Information & communication | 2025 |
| MK Surgical Services Limited | Health & social care | 2009 |
| MK2 Homes Limited | Construction | 2024 |
| MKD Estates LLP | | 2013 |
| MKF London Limited | Other services | 2018 |
| MKG Ventures Ltd | Real estate | 2026 |
| Mladenburg Ltd | Wholesale & retail | 2025 |
| MLH Electrical Services Ltd | Extraterritorial | 2021 |
| MLX Consulting Ltd | Professional & scientific | 2017 |
| MM & MM Limited | Administrative & support | 2023 |
| Mmad Limited | Manufacturing | 1997 |
| Mmor Medicines Limited | Wholesale & retail | 2016 |
| Mmti Ltd | Professional & scientific | 2012 |
| MNA Pharma Ltd | Wholesale & retail | 2023 |
| MNB Investments Ltd | Real estate | 2021 |
| MNP Real Estate Limited | Real estate | 2021 |
| MNT Catering Equipment UK Ltd | Hospitality | 2013 |
| Mobile Diary Ltd | Health & social care | 2013 |
| Mobile Pet Vaccination Service Ltd | Professional & scientific | 2021 |
| MOC Medical Ltd | Health & social care | 2022 |
| Modatech Ltd | Wholesale & retail | 2012 |
| Model Brickwork Limited | Construction | 2003 |
| Modgil Consulting Limited | Information & communication | 2017 |
| Modz Property Limited | Real estate | 2025 |
| Mohammed B Ltd | Health & social care | 2022 |
| Moksha Fire System Limited | Public administration | 2026 |
| Mollison Investments Limited | Real estate | 2016 |
| Monadana Ltd | Other services | 2013 |
| Monday Property Management Ltd | Real estate | 2025 |
| Mondial Marmi Ltd | Mining & quarrying | 2021 |
| Mondo Construct Ltd | Extraterritorial | 2018 |
| Moneyspider Consultancy Limited | Professional & scientific | 1999 |
| Monica Hanouka Nutrition Ltd | Health & social care | 2021 |
| Monkey Ltd | Wholesale & retail | 2024 |
| Monkhouse Advisory Ltd | Health & social care | 2026 |
| Monoiluk Limited | Professional & scientific | 2016 |
| Monor House Court Ltd | Real estate | 2024 |
| Monsoons Book Club Limited | Information & communication | 2015 |
| Montazah LLP | | 2023 |
| Montrose Furniture Limited | Manufacturing | 1994 |
| Monty Global Payments Limited | Financial services | 2016 |
| Monty T Ltd | Professional & scientific | 2021 |
| Moonji Ltd | Manufacturing | 2018 |
| Moorland Services Ltd | Construction | 2024 |
| Morecona Limited | Wholesale & retail | 2017 |
| Morfa CH Ltd | Real estate | 2024 |
| Morgan Berkeley Consulting Limited | Extraterritorial | 2018 |
| Morgan Berkeley Group Limited | Professional & scientific | 2000 |
| Morgan Berkeley HR Limited | Administrative & support | 2022 |
| Morgan Berkeley Limited | Professional & scientific | 1992 |
| Morgan Berkeley OMQ Limited | Extraterritorial | 1998 |
| Morgan Rutherford Associates Limited | Administrative & support | 1996 |
| Moriche Caterers Limited | Hospitality | 1973 |
| Moris Investments Ltd | Health & social care | 2023 |
| Morish Ltd | Professional & scientific | 2024 |
| Morland House Healthcare Limited | Wholesale & retail | 2019 |
| MOS Catering Limited | Hospitality | 2026 |
| Moss Goodman Limited | Professional & scientific | 2008 |
| MOT and Services Centre Ltd | Wholesale & retail | 2022 |
| Motam Limited | Wholesale & retail | 2026 |
| Mothership Drinks Ltd | Professional & scientific | 2024 |
| Motion Broker Limited | Transport & logistics | 2018 |
| Motor-Inn Limited | Wholesale & retail | 1990 |
| Motorway Lions Ltd | Wholesale & retail | 2026 |
| Mottingham Healthcare Ltd | Wholesale & retail | 2023 |
| Mould Rescue Limited | Administrative & support | 2024 |
| Moulin Rouge Properties Limited | Real estate | 2006 |
| Mount Sutherland Holdings Limited | Financial services | 2020 |
| Mount Talbot Communications Limited | Professional & scientific | 2018 |
| Mountview Trading Ltd | Hospitality | 2010 |
| Movegevity Ltd | Health & social care | 2026 |
| Moving Parts Logistics Ltd | Water & waste | 2025 |
| MP Healthcare Limited | Health & social care | 2025 |
| MP5 Limited | Real estate | 2019 |
| MPJ SLS Limited | Real estate | 2022 |
| MPL Group Properties Ltd | Real estate | 2023 |
| MR & MRS Developments 1 Limited | Real estate | 2021 |
| MR Scissorhand Limited | Other services | 2024 |
| Mrcpch Clinical Ltd | Education | 2017 |
| MRE Group (London) Ltd | Construction | 2015 |
| MRP Construction Ltd | Manufacturing | 2025 |
| MS 380 Limited | Administrative & support | 1988 |
| MS Exhibition Services Ltd | Construction | 2010 |
| MS7VENTURECO Limited | Professional & scientific | 2025 |
| Msah Capital Ltd | Real estate | 2023 |
| MSB Diagnostics Ltd | Health & social care | 2022 |
| MSB Fashion Limited | Wholesale & retail | 2017 |
| MSC Primary Care Limited | Health & social care | 2023 |
| MSJ Consultants Limited | Professional & scientific | 2010 |
| Msjalondon Ltd | Real estate | 2018 |
| Msjp Limited | Construction | 2018 |
| MSM Realty Ltd | Real estate | 2025 |
| Msmwholesalers Ltd | Wholesale & retail | 2025 |
| Mspine Holding Ltd | Professional & scientific | 2025 |
| Mspine LLP | | 2024 |
| MSW Construction Limited | Construction | 2005 |