| Mediatrix Limited | Professional & scientific | 2012 |
| Medibike Limited | Health & social care | 2011 |
| Medical Aesthetics Training Ltd | Health & social care | 2011 |
| Medical Design Group Ltd | Professional & scientific | 2022 |
| Medicath Ltd. | Professional & scientific | 1997 |
| Medina Electronics Design Consultancy Ltd | Manufacturing | 2022 |
| Medina Financial Solutions Limited | Financial services | 2013 |
| Medina Gardens Management Limited | Households | 2004 |
| Medina Shipping Ltd | Transport & logistics | 2025 |
| Medina View (Horseshoe) RTM Company Limited | Households | 2011 |
| Medina View Marina Apartments (12-31) RTM Company Ltd | Households | 2011 |
| Medispaone Ltd | Other services | 2015 |
| Medium Art Ltd | Wholesale & retail | 2026 |
| Medivatus UK Limited | Other services | 2016 |
| Medrau Maindee Makers CIC | Manufacturing | 2025 |
| Meed Care Limited | Health & social care | 2021 |
| Meese Farming Limited | Agriculture & fishing | 1997 |
| MEG Jones Rugby Ltd | Arts & recreation | 2025 |
| Mega Yacht Solutions Limited | Administrative & support | 2010 |
| Mehevin Limited | Real estate | 2025 |
| Meirion C Promotions Ltd | Arts & recreation | 2025 |
| Mekon Events Ltd | Arts & recreation | 2022 |
| Mel's Logistics Ltd | Transport & logistics | 2025 |
| Melcombe House Management Company Limited | Households | 1998 |
| Melloy (Holdings) Limited | Professional & scientific | 2011 |
| Melon Dosh Promotions Limited | Arts & recreation | 2003 |
| Meltek (Leicester) Limited | Extraterritorial | 1990 |
| Melville Court Management Company (Ryde) Limited | Households | 1990 |
| MEN2BEHEALTH Ltd | Health & social care | 2020 |
| Menarich Investments Ltd | Administrative & support | 2017 |
| Menter Iaith Casnewydd | Education | 2014 |
| Mentur.Io Ltd | Administrative & support | 2018 |
| Mercator Partnership Limited | Professional & scientific | 2004 |
| Mercer Pellard Properties Limited | Real estate | 2022 |
| Mercia Safety Ltd | Professional & scientific | 2025 |
| Mercury Windows and Doors Limited | Construction | 2013 |
| Mere Park Valeting Ltd | Other services | 2020 |
| Meredith Motors Ltd | Wholesale & retail | 2019 |
| Merge Ready Ltd | Information & communication | 2025 |
| Meridian 3 Limited | Manufacturing | 2020 |
| Meridian Design & Build Ltd | Construction | 1997 |
| Merlin Supplies Limited | Wholesale & retail | 2015 |
| Merlord Ltd | Information & communication | 2026 |
| Mermaid Accommodation Limited | Hospitality | 2020 |
| Mermaid Laundry Ltd | Other services | 2020 |
| Mersea Skincare Ltd | Other services | 2024 |
| Merthyr (South Wales) Limited | Construction | 2001 |
| Merthyr Electro-Plating Co. Limited | Manufacturing | 1964 |
| Meta Distribution Holdings Ltd | Wholesale & retail | 2022 |
| Metafinity Limited | Financial services | 2022 |
| Metatown Ltd | Information & communication | 2022 |
| Metco Global Ltd | Professional & scientific | 2020 |
| Meteclass Ltd | Wholesale & retail | 2025 |
| Metromend Motors Newport Ltd | Wholesale & retail | 2025 |
| MEW the Movers Ltd | Transport & logistics | 2024 |
| Mews Court Management Company Limited | Households | 2005 |
| Mews Estates Limited | Real estate | 2018 |
| Mezex Ltd | Construction | 2020 |
| Mezz-A-Rise Construction Ltd | Construction | 2024 |
| MFA Security Services Ltd | Administrative & support | 2025 |
| MFD Agriculture Limited | Agriculture & fishing | 2010 |
| MFD Investments Limited | Financial services | 2025 |
| MG Construction IW Ltd | Construction | 2024 |
| MG Group IW Ltd | Financial services | 2024 |
| MG Ryan Properties Limited | Real estate | 2024 |
| MG Scenic Painting Limited | Arts & recreation | 2023 |
| MG Transit Ltd | Transport & logistics | 2025 |
| MGA Express Limited | Transport & logistics | 2022 |
| Mgem Ltd | Professional & scientific | 2014 |
| MGH IOW Holdings Ltd | Financial services | 2026 |
| MGN IW Limited | Real estate | 2020 |
| Mgps Holdings Limited | Other services | 2016 |
| Mgroup Accommodation Ltd | Real estate | 2022 |
| Mgscaffold UK Ltd | Construction | 2019 |
| MH Investments 2022 Limited | Financial services | 2022 |
| Mhmuzaffar Limited | Health & social care | 2019 |
| MHO Properties Ltd | Hospitality | 2026 |
| MHS Supplies Ltd | Wholesale & retail | 2024 |
| MIA Management Limited | Administrative & support | 2002 |
| Miah Family Properties (IOW) Limited | Real estate | 2025 |
| Miah Logistics Ltd | Transport & logistics | 2024 |
| Miah Van Rentals Ltd | Administrative & support | 2025 |
| Mian Nexus Group Ltd | Manufacturing | 2025 |
| Michael Ellis Williams Ltd | Professional & scientific | 2025 |
| Michael Jones Estate Agents Limited | Real estate | 2002 |
| Michael Pratt Project Management Ltd | Professional & scientific | 2022 |
| Michael West & SON Ltd | Manufacturing | 2024 |
| Michael Wheatle Ltd | Real estate | 2010 |
| Micheal Kayiwa Ltd | Other services | 2021 |
| Michelina Ltd | Wholesale & retail | 2024 |
| Mickey ADE Ltd | Wholesale & retail | 2026 |
| Micore Solutions Limited | Administrative & support | 2015 |
| Microengine Limited | Professional & scientific | 2025 |
| Microsmith Electronics Ltd | Information & communication | 2015 |
| MID Glam Packing Supplies Limited | Wholesale & retail | 1982 |
| Mid-Glam Construction Limited | Construction | 1978 |
| Middle East Trade Company Limited | Professional & scientific | 2013 |
| Midicake Ltd | Manufacturing | 2021 |
| Midland Alpha Internet Services Limited | Information & communication | 1997 |
| Midlands Accountants Limited | Professional & scientific | 2004 |