| Milligan Ellory Limited | Professional & scientific | 2010 |
| Millrace Marketing Limited | Wholesale & retail | 2002 |
| Miltonsix Limited | Arts & recreation | 2010 |
| Milverton Grove Ltd | Real estate | 2017 |
| Mimosa Consulting Ltd | Professional & scientific | 2019 |
| Minae Consulting Limited | Professional & scientific | 2017 |
| Mindsetrx Ltd | Health & social care | 2022 |
| Minerva Therapy Rooms Ltd | Other services | 2021 |
| Minick Railway Signalling Limited | Professional & scientific | 2011 |
| Mintivo Group Limited | Professional & scientific | 2026 |
| Mintivo Ltd | Information & communication | 2015 |
| Mipermit Limited | Information & communication | 2009 |
| Mirabilia Limited | Wholesale & retail | 2003 |
| Miratis Ltd | Wholesale & retail | 2010 |
| Miris Property Ltd | Construction | 2020 |
| Mirrorless Limited | Information & communication | 2020 |
| Mirwood Ltd | Professional & scientific | 2015 |
| Miss Ballooniverse Limited | Arts & recreation | 2011 |
| Mistress Persephone's Apothecary Limited | Wholesale & retail | 2026 |
| Mitchell Windows Limited | Construction | 2014 |
| MJ Church Holdings Limited | Financial services | 2024 |
| MJ Church Recycling Limited | Mining & quarrying | 2013 |
| MJB Plant Services Ltd | Manufacturing | 2021 |
| MJG Building Services Limited | Construction | 2007 |
| MJG Kitchens Ltd | Administrative & support | 2014 |
| MJH Consulting (London) Ltd | Financial services | 2019 |
| MJH Finsys Limited | Professional & scientific | 2015 |
| MJH UK Holdings Limited | Financial services | 2023 |
| MK Group Holdings Ltd | Financial services | 2019 |
| MK1 Vehicle Detailing Ltd | Wholesale & retail | 2026 |
| MLC Systems Ltd | Transport & logistics | 2020 |
| MM Eyecare Holdings Limited | Wholesale & retail | 2020 |
| MMF Supreme Custom Ltd | Wholesale & retail | 2021 |
| MMS Consulting Ltd | Information & communication | 2015 |
| MMT Services Limited | Agriculture & fishing | 1986 |
| Mobile Caravan Engineers Associates Ltd | Other services | 2008 |
| Mobile Farrier Services Limited | Agriculture & fishing | 2013 |
| Mobius Logistics Ltd | Transport & logistics | 2019 |
| Mobius Technology Ltd | Transport & logistics | 2014 |
| Mobiux Labs UK Limited | Information & communication | 2016 |
| Modaxo Group UK Limited | Information & communication | 2001 |
| Modaxo Traffic Management UK Ltd | Information & communication | 2023 |
| Model Farm Eggs Limited | Wholesale & retail | 2012 |
| Model Melody Ltd | Other services | 2026 |
| Modish Installations Limited | Construction | 2019 |
| Modiva Clothing Ltd | Wholesale & retail | 2023 |
| Modular Essentials Ltd | Construction | 2010 |
| Mollrose Drive Ltd | Households | 2023 |
| Moloh Limited | Manufacturing | 2003 |
| Moloh Pimlico Limited | Extraterritorial | 2009 |
| Moloney Contractors Limited | Construction | 2014 |
| Momentum Home Physiotherapy Services Ltd | Health & social care | 2026 |
| Mongoose Productions Ltd | Information & communication | 2021 |
| Monitor Computing Services Limited | Information & communication | 1997 |
| Monmax Hospitality Consulting Limited | Information & communication | 2023 |
| Monsieur Charming Music Ltd | Information & communication | 2024 |
| Montresor Partnership LLP | | 2009 |
| Monty Trading Limited | Wholesale & retail | 2015 |
| Moontron Limited | Real estate | 1995 |
| Moorgate Consulting Limited | Professional & scientific | 2011 |
| Moose Hall Wellness Chippenham Limited | Health & social care | 2019 |
| Morning Star Motors Limited | Financial services | 1962 |
| Morris Lawns Limited | Administrative & support | 2023 |
| Morse Renovations Ltd | Construction | 2019 |
| Mortgage Advice Bureau South West Ltd | Financial services | 2000 |
| Mosaic One Limited | Information & communication | 2025 |
| Moses Tawo Legal Services Limited | Professional & scientific | 2024 |
| Mosman Consulting Ltd | Professional & scientific | 2023 |
| Motherlode Media Ltd | Information & communication | 2007 |
| Motion 7 Limited | Information & communication | 2007 |
| Motley Investments Limited | Professional & scientific | 2000 |
| Moto 44 Ltd | Other services | 2024 |
| Motorholics Limited | Wholesale & retail | 2018 |
| Motoxtreme Motoland Ltd | Arts & recreation | 2024 |
| Move Easy Mortgages Limited | Financial services | 2020 |
| Movement and Mind Ltd | Education | 2022 |
| Moving Elephants Limited | Information & communication | 2015 |
| Mozzaology Ltd | Other services | 2021 |
| MP Speech and Language Therapy Services Ltd | Health & social care | 2024 |
| MPL Resources Ltd | Construction | 2004 |
| MRA Law Ltd | Professional & scientific | 2023 |
| MRP Properties Wiltshire Ltd | Real estate | 2025 |
| MRT Independent Limited | Administrative & support | 2005 |
| MS Software Development Ltd | Information & communication | 2024 |
| MSA 365 Limited | Information & communication | 2016 |
| Msasa Consulting Ltd | Wholesale & retail | 1995 |
| Msea Ltd | Manufacturing | 2024 |
| MSJ Project Ltd | Administrative & support | 2002 |
| Mtetwa Associates Limited | Professional & scientific | 2008 |
| Muasasat Mulkern Ltd | Education | 2023 |
| Mudrak & Sons Limited | Wholesale & retail | 2019 |
| Muggi Limited | Manufacturing | 2010 |
| Mulberry Financial Services Limited | Extraterritorial | 2007 |
| Multiquip Property Limited | Professional & scientific | 2024 |
| Multiquip Supplies Limited | Wholesale & retail | 2002 |
| Murray Financial Partnering Ltd | Professional & scientific | 2024 |
| Murray&Gould Ltd | Manufacturing | 2022 |
| Muso Mirror Limited | Manufacturing | 2017 |
| MW Elite Kickboxing Ltd | Arts & recreation | 2025 |
| MW High Tech Projects UK Limited | Construction | 2004 |