| Meadway Court Management (Teddington) Limited | Households | 1973 |
| Meaningful Silver Jewellery Ltd | Manufacturing | 2024 |
| Meat Market Barbecue Ltd | Hospitality | 2024 |
| Meat Studio Ltd | Professional & scientific | 2013 |
| Med-Chef Limited | Hospitality | 2021 |
| Medapp Dynamics Limited | Health & social care | 2021 |
| Medee Events Limited | Professional & scientific | 2025 |
| Medevala Pharma Limited | Wholesale & retail | 2013 |
| Media by Malik Ltd | Information & communication | 2025 |
| Media Exchange Group Ltd | Professional & scientific | 2019 |
| Media House Solutions Ltd | Information & communication | 2021 |
| Media Interactive Europe Limited | Professional & scientific | 1999 |
| Media Interactive Limited | Information & communication | 1999 |
| Media Recruit Ltd | Professional & scientific | 2025 |
| Mediand Limited | Professional & scientific | 2012 |
| Mediastudio Presentations Limited | Manufacturing | 2002 |
| Mediaxg UK Ltd | Professional & scientific | 2021 |
| Medical Consultant Services Limited | Administrative & support | 2016 |
| Medical Empathy Ltd | Health & social care | 2024 |
| Medimarvel Recruitment Network Ltd | Administrative & support | 2024 |
| Medina House (Milton Keynes) RTM Company Limited | Real estate | 2023 |
| Medusa Homes Limited | Other services | 2020 |
| Medway Wholesale Meats Limited | Wholesale & retail | 1999 |
| Meeyeow Ltd | Professional & scientific | 2021 |
| Mega's Butterflies Ltd | Health & social care | 2023 |
| Meggie Care Recruitment Limited | Health & social care | 2021 |
| Mehr Property Investments Ltd | Real estate | 2023 |
| MEK Aqua Ltd | Extraterritorial | 2024 |
| MEL & JEM Ltd | Other services | 2016 |
| Melanko Ltd | Extraterritorial | 2023 |
| Melatan Ltd | Other services | 2025 |
| Melbury Holdings Limited | Real estate | 1999 |
| Melete Consulting Limited | Information & communication | 2021 |
| Mellin Property Ltd | Real estate | 2019 |
| Melrose House RTM Company Limited | Households | 2016 |
| Memory Capsule Limited | Administrative & support | 2025 |
| MEN United Support Program Ltd | Administrative & support | 2025 |
| Mena Valley Services UK Ltd | Professional & scientific | 2024 |
| Menan Ltd | Wholesale & retail | 2023 |
| Mendip Houses (Welwyn Street) Limited | Households | 2003 |
| Mendoza Wine Imports Limited | Wholesale & retail | 2023 |
| Meopham Court (Beckenham Grove) Management Limited | Households | 1970 |
| MEP Property Group Limited | Real estate | 2022 |
| Mera Construction Limited | Financial services | 2018 |
| Merbur Ltd | Real estate | 2022 |
| Mercan Coffee Limited | Hospitality | 2024 |
| Mercantile Legal Services Limited | Professional & scientific | 1973 |
| Mercer AI Healthcare Solutions Ltd | Information & communication | 2024 |
| Mercer Bridge Limited | Administrative & support | 2006 |
| Mercer Estates Ltd | Real estate | 2020 |
| Merchant-Edge UK Ltd | Professional & scientific | 2020 |
| Mercurius Health UK Ltd | Financial services | 2024 |
| Meridian Construction Ltd | Construction | 2015 |
| Merkhet Ltd | Professional & scientific | 2026 |
| Merlin Research Limited | Real estate | 2000 |
| Merryllyn Consults Limited | Professional & scientific | 2021 |
| Merve-Ra Ltd | Extraterritorial | 2023 |
| Meshwani Traders Ltd | Wholesale & retail | 2025 |
| Messenger's French Polishing Limited | Construction | 2016 |
| Messeter Place Management Company Limited | Real estate | 2014 |
| Meta Green Energy Limited | Professional & scientific | 2025 |
| Metalheads Limited | Other services | 2013 |
| Metier by Tomfoolery Limited | Wholesale & retail | 2014 |
| Metin Kicir Ltd | Extraterritorial | 2024 |
| Meto Properties Ltd | Real estate | 2025 |
| Metra Solutions Ltd | Construction | 2024 |
| Metrix AI Ltd | Health & social care | 2025 |
| Metropole (Folkestone) Limited | Real estate | 1995 |
| Metropolitan Maintenance Ltd | Construction | 2017 |
| Metropolitan Police Hayes Sports Club Limited | Arts & recreation | 2008 |
| Mets Holding Co Limited | Hospitality | 2026 |
| Mewell Ltd | Professional & scientific | 2019 |
| Mexfield Solutions Ltd | Information & communication | 2022 |
| Mezra Finance Limited | Professional & scientific | 1994 |
| Mezra Limited | Professional & scientific | 2005 |
| Mezzanine Media Ltd | Wholesale & retail | 2016 |
| MFL Services Ltd | Administrative & support | 2024 |
| Mfoa Limited | Professional & scientific | 2025 |
| Mfsp Holdings Limited | Professional & scientific | 2010 |
| MG Bromley Services Ltd | Other services | 2024 |
| MG Genone Developments Limited | Construction | 2025 |
| MGA Construction Consultancy Services Limited | Construction | 2009 |
| Mgielevator Ltd | Construction | 2016 |
| Mgpl Ortho Ltd | Health & social care | 2022 |
| MGS Property & Catering Limited | Real estate | 2015 |
| MH Broker Services Limited | Financial services | 2024 |
| MH Landscape Solutions Limited | Construction | 2020 |
| MH Property Renovations Ltd | Construction | 2024 |
| MHK Asset Management Ltd | Real estate | 2025 |
| Mhnile UK Ltd | Health & social care | 2025 |
| MI9 Enterprises Ltd | Hospitality | 2022 |
| MIA Novel Idea Media Limited | Professional & scientific | 2006 |
| Mia's Marketplace Ltd | Wholesale & retail | 2026 |
| Miatti Maritime Limited | Extraterritorial | 2017 |
| MIB Accountants Limited | Professional & scientific | 2006 |
| Michael Roberts Homes Ltd | Real estate | 2021 |
| Michael Venner Creative Ltd | Professional & scientific | 2025 |
| Michelle Sidwell Academy of Dance Ltd | Arts & recreation | 2024 |
| Michin Limited | Professional & scientific | 2014 |
| Micks Cafe Limited | Hospitality | 2025 |