| Melisanur Ltd | Hospitality | 2025 |
| Mentall Marketing Ltd | Professional & scientific | 2001 |
| MEP Environmental Limited | Professional & scientific | 2026 |
| Merit Oral Ltd | Health & social care | 2026 |
| Meritor Aftermarket Europe Limited | Wholesale & retail | 2020 |
| Meritor Electric Powertrain Systems UK Limited | Professional & scientific | 2021 |
| Meritor Heavy Vehicle Braking Systems (UK) Limited | Manufacturing | 1998 |
| Meritor Holdings UK Ltd. | Manufacturing | 2016 |
| Merryfield Kitchens Limited | | 1982 |
| Mesh.P Limited | Wholesale & retail | 2026 |
| MGJ Building Services Limited | Construction | 2025 |
| MH Construction Services (Wales) Ltd | Professional & scientific | 2009 |
| MHR Trend Limited | Manufacturing | 2025 |
| MI Fragrance Fusion Ltd | Manufacturing | 2024 |
| Mi-Events Ltd | Hospitality | 2023 |
| Michael Harding Art Formulas Limited | Manufacturing | 2004 |
| Michaelmas Consulting Limited | Professional & scientific | 2007 |
| Midas Display Systems Limited | Construction | 2002 |
| Midnight Design and Consultancy Ltd | Professional & scientific | 2021 |
| Mike Jones & Associates Limited | Professional & scientific | 2013 |
| Mindful Munch Cafe LLP | | 2025 |
| Ministry of Adventures - Solo Sisters Limited | Administrative & support | 2024 |
| Minnows Touring Park Limited | Hospitality | 2016 |
| Miriefe Ltd | Professional & scientific | 2024 |
| Misfit & Weird DAD Distribution Ltd | Wholesale & retail | 2024 |
| Mito Developments (SW) Ltd | Construction | 2018 |
| MJ & PM Properties Limited | Real estate | 2015 |
| MJW UK Group Ltd | Manufacturing | 2016 |
| Mkingfs Ltd | Financial services | 2006 |
| MLS Services Limited | Administrative & support | 2018 |
| MM Sporting Limited | Wholesale & retail | 2011 |
| MNC Projects Ltd | Wholesale & retail | 2026 |
| Mnlv Ltd | Agriculture & fishing | 2016 |
| Mobile Tracking Systems Limited | Information & communication | 2000 |
| Modelhub Solutions Limited | Information & communication | 2026 |
| Modern Media Collective Ltd | Manufacturing | 2025 |
| MON and Border Motor Factors Limited | Wholesale & retail | 1968 |
| Monkswood Estate Management Limited | Administrative & support | 1997 |
| Monmouthshire Roofing and Guttering Ltd | Construction | 2022 |
| Monmouthshire Show Society Limited | Arts & recreation | 1976 |
| Monmouthshire Storage Ltd | Transport & logistics | 2023 |
| Moonsys Technology Limited | Manufacturing | 2003 |
| Moore Storage 1965 Limited | Transport & logistics | 2020 |
| Moorlands & Manors Country Clothing Ltd | Wholesale & retail | 2023 |
| Moose Enterprises Limited | Wholesale & retail | 2014 |
| Moose Holdco (UK) Limited | Wholesale & retail | 2014 |
| MOR Development & Compliance Ltd | Professional & scientific | 2025 |
| Morgan & Co. Renovations Ltd | Construction | 2023 |
| Morgan Rose Developments Ltd | Construction | 2019 |
| Morgan's B&B Ltd | Hospitality | 2017 |
| Morspan Construction Limited | Construction | 2006 |
| Mortgages-M-E Ltd | Financial services | 2021 |
| Moruzzi Landscapes Limited | Administrative & support | 2023 |
| Motoclean Ltd | Other services | 2025 |
| Motor Trade Technologies Limited | Information & communication | 2005 |
| Motorsense Commercial Limited | Wholesale & retail | 2026 |
| Motun & Niyi Propertyinvestments Ltd | Real estate | 2026 |
| Mountaintop Education and Skills Training Limited | Education | 2025 |
| Movefituk Ltd | Health & social care | 2017 |
| Movehive Ltd | Administrative & support | 2026 |
| MPP (Newport) Ltd | Administrative & support | 2024 |
| MR Chippy Ltd | Hospitality | 2026 |
| MRA Design Studio Ltd | Professional & scientific | 2024 |
| MRB Partners Ltd | Manufacturing | 2010 |
| MRP Utilities Ltd | Construction | 2026 |
| MSH Building Ltd | Construction | 2007 |
| MSH Group Holdings Limited | Financial services | 2025 |
| MSH Property Developments Limited | Construction | 2018 |
| MSP Technical Holdings Ltd | Real estate | 2023 |
| MSP Technical Services Ltd | Professional & scientific | 2019 |
| MSR Renovations CYF | Administrative & support | 2025 |
| Muharob Investments Limited | Real estate | 2022 |
| Murmuration Dynamics Ltd | Information & communication | 2024 |
| Muttley Crew Dog Training & Behaviour Limited | Other services | 2023 |
| MV Business Services Limited | Professional & scientific | 2024 |
| My Letting Agent Limited | Real estate | 2020 |
| My Local Convenience Stores Limited | Wholesale & retail | 2016 |
| My Local Convenience Stores Malpas Ltd | Wholesale & retail | 2022 |
| N C Steel Limited | Manufacturing | 2017 |
| N G Construction Limited | Construction | 2003 |
| Nagra Media UK Limited | Information & communication | 2005 |
| Nalv Ltd | Real estate | 2024 |
| NBL Properties Limited | Real estate | 2025 |
| NC Sushi Limited | Wholesale & retail | 2024 |
| NE Ventilation Limited | Construction | 2025 |
| Neale Catering Ltd | Hospitality | 2025 |
| Neat Feet Footcare Ltd | Health & social care | 2022 |
| Neetha's Kitchen Ltd | Hospitality | 2024 |
| Neil Desmond Productions Ltd | Information & communication | 2025 |
| Neomatrix Software Solutions Limited | Information & communication | 2019 |
| Nephesh Limited | Real estate | 1997 |
| Nest Creche Limited | Health & social care | 2026 |
| NET Zero Carbon Solutions Limited | Administrative & support | 2016 |
| Netfusion Connect Limited | Information & communication | 2024 |
| New Dairy Farm Limited | Agriculture & fishing | 2021 |
| New Life Painting and Decorating Limited | Construction | 2025 |
| New Park Farm Energy Limited | Energy | 2011 |
| New Vision Techno Ltd | Information & communication | 2020 |
| Newbold Holdings Limited | Extraterritorial | 2025 |
| Newbold Properties Limited | Professional & scientific | 2011 |