| Mendahose Holdings Limited | Financial services | 2020 |
| Mendahose Hydraulics Limited | Manufacturing | 1988 |
| Meng.Ai Ltd | Information & communication | 2026 |
| Mens Method Ltd | Manufacturing | 2023 |
| Mensah White Management Ltd | Real estate | 2022 |
| Mental Health at Work C.I.C. | Professional & scientific | 2016 |
| Mental Health Tick Ltd | Education | 2020 |
| Mentorport Limited | Professional & scientific | 1983 |
| Meon Car Storage Ltd | Transport & logistics | 2026 |
| Meon Coaching and Consulting Limited | Other services | 2015 |
| Meon Homes Limited | Construction | 2014 |
| Meon One LP | | 2004 |
| Meon Two LP | | 2005 |
| Meon Valley Accounting Limited | Professional & scientific | 2020 |
| Meon Valley Carpentry Ltd | Construction | 2026 |
| Meon Valley Electrical & Building Service Limited | Construction | 2025 |
| Meon Valley Garage Doors Ltd. | Construction | 2015 |
| Meon Valley Honey Ltd | Agriculture & fishing | 2023 |
| Meon Valley Inns Limited | Hospitality | 2020 |
| Meon Valley Law Limited | Professional & scientific | 2026 |
| Meon Valley Mowers Ltd | Manufacturing | 2021 |
| Meon Valley Surfacing Ltd | Construction | 2021 |
| Meon Valley Times Limited | Information & communication | 2021 |
| Meon Valley Window Cleaning Ltd | Administrative & support | 2011 |
| Meonstoke Tennis Club Ltd | Arts & recreation | 2014 |
| Meontech Recruitment Ltd | Professional & scientific | 2018 |
| Meonvalley Medical Aesthetics Limited | Health & social care | 2024 |
| MER Spedition Ltd | Transport & logistics | 2018 |
| Mera Developments Limited | Construction | 2023 |
| Meraki Beauty Studio Limited | Other services | 2017 |
| Meraki Creative Systems Ltd | Professional & scientific | 2025 |
| Meravis Care Ltd | Extraterritorial | 2024 |
| Mercari Risk Holdings Limited | Professional & scientific | 2018 |
| Mercari Risk Management International Limited | Financial services | 2019 |
| Mercari Risk Management Ltd | Financial services | 2017 |
| Mercator Crewing UK Limited | Administrative & support | 2024 |
| Mercfly Limited | Transport & logistics | 2025 |
| Merchandise Matters Ltd | Wholesale & retail | 2013 |
| Merchant AI Limited | Information & communication | 2023 |
| Merchant Events Limited | Hospitality | 2014 |
| Merchant Navy Welfare Board(The) | Health & social care | 1948 |
| Merchant Place (Winchester) Management Company Limited | Households | 1997 |
| Merchant Trading Company Limited | Financial services | 2005 |
| Merchant's Gastro Limited | Hospitality | 2013 |
| Mercury Contract Flooring Limited | Construction | 2014 |
| Mercury Installations Limited | Professional & scientific | 1989 |
| Mercury Systems Engineers Limited | Information & communication | 1985 |
| Mercury Systems Limited | Professional & scientific | 1989 |
| Mercury Waste UK Ltd | Water & waste | 2025 |
| MERCURY087 Limited | Administrative & support | 2022 |
| Mercy Collective UG C.I.C. | Wholesale & retail | 2025 |
| Meridian Accountants Limited | Professional & scientific | 2026 |
| Meridian Automotive Services Limited | Wholesale & retail | 2026 |
| Meridian Contract Services Limited | Administrative & support | 1993 |
| Meridian Corporate Finance Limited | Financial services | 2014 |
| Meridian Court Management Company Limited | Households | 1992 |
| Meridian Growth Capital LLP | | 2018 |
| Meridian Growth Consultants LLP | | 2025 |
| Meridian Investors LLP | | 2009 |
| Meridian IP Communications Limited | Information & communication | 2008 |
| Meridian Property Holding Ltd | Real estate | 2021 |
| Meridian Roofing Limited | Construction | 2015 |
| Meridian Technique Limited | Information & communication | 1997 |
| Meridian Training and Development Limited | Information & communication | 1999 |
| Meridien Jewels Ltd | Wholesale & retail | 2026 |
| Meringtons UK Ltd | Real estate | 2025 |
| Meriton Associates Limited | Other services | 2015 |
| Merkarto Sphere Ltd | Wholesale & retail | 2025 |
| Merlin Homes (Southern) Limited | Real estate | 2017 |
| Merlin Homes (Westbourne) Ltd | Construction | 2023 |
| Merlin IT Contract Services Ltd | Information & communication | 2014 |
| Merlin Technical Ltd | Construction | 2018 |
| Merlin's Beverages Limited | Wholesale & retail | 2015 |
| Mermaid Court Management Company Limited | Households | 1986 |
| Merrion Sands Limited | Extraterritorial | 2003 |
| Merritt Tree Specialists Ltd | Agriculture & fishing | 2003 |
| Merritts Mill Limited | Hospitality | 2018 |
| Merryhill Envirotec Limited | Water & waste | 1992 |
| Merrythorn Electrical Ltd | Construction | 2025 |
| Merstone Hall Limited | Health & social care | 2007 |
| MES - CP Ltd | Professional & scientific | 2025 |
| MES Group (Southern) Limited | Financial services | 2019 |
| Mesc Investments Limited | Construction | 2021 |
| Mesea Properties Limited | Real estate | 2018 |
| Meshack Gumede Limited | Health & social care | 2014 |
| Meshed Insights Limited | Professional & scientific | 2013 |
| Meshed Management Limited | Real estate | 2014 |
| Mesini Ltd | Health & social care | 2020 |
| Messham Collings Limited | Real estate | 2022 |
| Messinger Holdings Ltd | Wholesale & retail | 2024 |
| Meta Environmental Ltd | Professional & scientific | 2019 |
| Metacornerstone (Southampton) Ltd | Wholesale & retail | 2022 |
| Metadata Management Services Limited | Information & communication | 2002 |
| Metals Regulation Limited | Professional & scientific | 2021 |
| Metamight Solutions Limited | Information & communication | 2025 |
| Metcalfe’S Metal Craft Ltd | Other services | 2018 |
| Meteor Market Ltd | Wholesale & retail | 2020 |
| Methos Limited | Real estate | 2025 |
| Methsa Ltd | Health & social care | 2025 |
| Metis Corporate Education Limited | Professional & scientific | 2013 |