| Marwari Limited | Administrative & support | 2016 |
| Marybow Electrical Limited | Financial services | 2025 |
| Marymead Close Residents Association Limited | Households | 1994 |
| Maryna Ltd. | Health & social care | 2015 |
| MAS Locum Ltd | Health & social care | 2022 |
| Masakan Ltd | Wholesale & retail | 2022 |
| Masi Construction Limited | Construction | 2012 |
| Mason & Reynolds Holdings Limited | Real estate | 2018 |
| Maspero Media Ltd | Professional & scientific | 2021 |
| Masters Property Partners Ltd | Real estate | 2025 |
| Mastral Limited | Hospitality | 1993 |
| Matale Property Development Ltd | Construction | 2024 |
| Matei's Properties Ltd | Real estate | 2024 |
| Matei-Rgn Ltd | Administrative & support | 2018 |
| Mathew Acreman Live Audio Ltd | Information & communication | 2022 |
| Mathind (Commercial) Limited | Real estate | 1983 |
| Mathind Limited | Real estate | 1976 |
| Matrix Nutrition Limited | Wholesale & retail | 2021 |
| Matrix Waste Limited | Water & waste | 2023 |
| Matt Proevo Ltd | Construction | 2024 |
| MATTBARKER701 Limited | Hospitality | 2015 |
| Matteddymech Engineering Limited | Professional & scientific | 2023 |
| Matteomech Engineering Limited | Professional & scientific | 2018 |
| Mattgk Transport Ltd | Transport & logistics | 2026 |
| Matthew Baker (Caravans) Limited | Hospitality | 1970 |
| Matthew Bruce Limited | Real estate | 1984 |
| Matthew Griffiths Ltd | Transport & logistics | 2025 |
| Matthew Groves Ltd | Real estate | 2025 |
| Matthew Scott Education & Arts Ltd | Education | 2015 |
| Matthew Tancock Limited | Arts & recreation | 2015 |
| Matthews Family Butchers Limited | Wholesale & retail | 2010 |
| Matthews Legacy Ltd | Real estate | 2026 |
| Matthews Property Ltd | Real estate | 2021 |
| Matt’S Motors Newport Limited | Wholesale & retail | 2017 |
| MAV Soundtracks Limited | Information & communication | 2015 |
| Maven (Cymru) Ltd | Information & communication | 2024 |
| Mavi Golbasi Ltd | Hospitality | 2025 |
| MAX Forell Properties Ltd | Real estate | 2026 |
| MAX Lahiff Media Ltd | Manufacturing | 2021 |
| MAX Potential Consulting Ltd | Professional & scientific | 2025 |
| Maxibay Limited | Wholesale & retail | 2014 |
| Maxicomms Limited | Transport & logistics | 2024 |
| Maxx Properties Ltd | Real estate | 2020 |
| Mayers and Shaw Ltd | Wholesale & retail | 2017 |
| Mayfair 184 Limited | Construction | 2020 |
| Mayflower Court Management Company Limited | Households | 1987 |
| Mayhew & Shaw Construction Ltd | Construction | 2015 |
| Mayo Marquee Hire Ltd | Administrative & support | 2024 |
| Maypole Garden Furniture Ltd | Wholesale & retail | 2025 |
| Maysix Health Partners Limited | Wholesale & retail | 2024 |
| Mayuri Consultant Services Limited | Information & communication | 2012 |
| MB Games Ltd | Arts & recreation | 2025 |
| Mb-Lec Limited | Construction | 2008 |
| Mbact Regeneration Limited | Arts & recreation | 2013 |
| MBC Hospitality Equipment Limited | Wholesale & retail | 2019 |
| MBH Carpentry & Building Ltd | Manufacturing | 2026 |
| Mbro Limited | Professional & scientific | 2002 |
| MC Creative Ltd | Professional & scientific | 2024 |
| MC Glazing Solutions Limited | Construction | 2023 |
| MC Rail Ltd | Construction | 2025 |
| MC Rental & Property Holdings Ltd | Real estate | 2025 |
| Mcbb Properties Limited | Real estate | 2023 |
| MCC Investments Ltd | Real estate | 1997 |
| Mccann's Rock Bar Limited | Hospitality | 2021 |
| Mccole & Co Plastering Ltd | Construction | 2025 |
| Mcdonald Carpentry Limited | Construction | 2015 |
| Mcgowan Consultancy Ltd | Professional & scientific | 2014 |
| Mcguinness Design Limited | Professional & scientific | 2023 |
| MCI Barbers Ltd | Other services | 2020 |
| MCL Environmental Services Limited | Professional & scientific | 2015 |
| MCL Sports Bars Ltd | Arts & recreation | 2020 |
| Mclavin Ltd | Wholesale & retail | 2026 |
| Mclellan Services Ltd | Construction | 2026 |
| Mcnayr Developments Limited | Construction | 2022 |
| MCS Finance Limited | Professional & scientific | 2020 |
| MD Building & Renovation Solutions Ltd | Construction | 2019 |
| MD Property Developements Limited | Real estate | 2017 |
| MD Waste Removal Services Ltd | Water & waste | 2022 |
| MDB Contract Carpentry Limited | Construction | 2018 |
| MDC Construction (Midlands) Ltd | Construction | 2014 |
| MDM Services (Cardiff) Limited | Manufacturing | 2001 |
| Mdok Properties Ltd | Real estate | 2022 |
| MDU Holdings Limited | Financial services | 2019 |
| MDW Holdings Limited | Transport & logistics | 2001 |
| ME LAH Group Ltd | Construction | 2019 |
| ME London Limited | Manufacturing | 2024 |
| Meadow View Contractors Limited | Construction | 2020 |
| Meadow View Developments IW Limited | Construction | 2014 |
| Meadow View Park (Cowes) Limited | Households | 2018 |
| Meadownook Residents Management Limited | Households | 1987 |
| Meadows Way Management Limited | Households | 2020 |
| Meadowstone Developments Ltd | Construction | 2023 |
| Mebbbo Ltd | Health & social care | 2025 |
| Mebz Limited | Transport & logistics | 2025 |
| Mechlink Autorepair Ltd | Wholesale & retail | 2025 |
| Meda-Han Ltd. | Wholesale & retail | 2017 |
| Medbay Neurocare Ltd. | Wholesale & retail | 2025 |
| Medellux Ltd | Manufacturing | 2018 |
| Medfile Limited | Professional & scientific | 2017 |
| Medham Management Limited | Households | 1990 |