| Martin Hopkins Partnership Limited | Administrative & support | 2003 |
| Martin Leon DIX Limited | Financial services | 2021 |
| Martin M Building Ltd | Energy | 2019 |
| Martin Player High Class Butcher Limited | Wholesale & retail | 2011 |
| Martin Property Consultants Limited | Professional & scientific | 2014 |
| Martinezonline Ltd | Wholesale & retail | 2024 |
| Martingales Intelligence Limited | Information & communication | 2025 |
| Martinova Ltd | Wholesale & retail | 2025 |
| Martvic Cleaning Services Ltd | Administrative & support | 2023 |
| Martwave Ltd | Manufacturing | 2007 |
| Marty Junior Madden Ltd | Construction | 2018 |
| Martyn Anderson Consulting Limited | Transport & logistics | 2012 |
| Martyn Carey GAS Maintenance Ltd | Construction | 2022 |
| Martyn Carey Plumbing & Heating Ltd | Construction | 2018 |
| Martyn Prowel Limited | Professional & scientific | 2001 |
| Martyn Shaw Ltd | Financial services | 2018 |
| Maruthi Quality Management Services Limited | Professional & scientific | 2023 |
| Maruti Restaurant and Grocery Ltd | Hospitality | 2023 |
| Marvel Plastering Services Ltd | Construction | 2019 |
| Marvello Ltd | Professional & scientific | 2025 |
| Marvellous and Sons Hope Limited Company Ltd | Health & social care | 2014 |
| Marvellous Cleans Ltd | Administrative & support | 2019 |
| Marvelous Cars Ltd | Wholesale & retail | 2021 |
| Marvin Thomas Properties Limited | Real estate | 2018 |
| Marv’S Couriers Ltd | Transport & logistics | 2020 |
| Marwent Ltd | Wholesale & retail | 2018 |
| Marwood Technical Services Limited | Professional & scientific | 2022 |
| Mary Bijou Cabaret Limited Partnership | | 2016 |
| Mary Corp Limited | Hospitality | 2025 |
| Mary Gold Ltd | Real estate | 2019 |
| Mary Hair & Beauty Ltd | Other services | 2019 |
| Maryam Arif Ltd | Wholesale & retail | 2025 |
| Maryam Consultancy UK Limited | Wholesale & retail | 2017 |
| Maryam Store Ltd | Wholesale & retail | 2019 |
| Maryamjahangir Limited | Wholesale & retail | 2023 |
| Mary’S Project Ltd | Construction | 2024 |
| Marz Music Limited | Information & communication | 2001 |
| MAS Bazaar Retail and Wholesale Limited | Wholesale & retail | 2019 |
| MAS Carpentry Co Ltd | Manufacturing | 2026 |
| MAS INT. Ltd | Administrative & support | 2018 |
| Masala Food Group Ltd | Hospitality | 2025 |
| Masala House Cardiff Ltd | Hospitality | 2026 |
| Masalya Ltd | Wholesale & retail | 2026 |
| Masasa Limited | Real estate | 2021 |
| Maschinen Weger Ltd | Wholesale & retail | 2026 |
| Masdaf Foodstuff Trading Ltd | Wholesale & retail | 2025 |
| Mash Pictures Ltd | Information & communication | 2021 |
| Mashiata Limited | Information & communication | 2026 |
| Mashona Limited | Wholesale & retail | 2025 |
| Masih Goals Ltd | Professional & scientific | 2025 |
| Masih Housing Ltd | Households | 2020 |
| Maskateertm Limited | Wholesale & retail | 2015 |
| Maskell, Moss & Co. Limited | Financial services | 2001 |
| Maskorea Ltd | Extraterritorial | 2016 |
| Maskreys Limited | Wholesale & retail | 1947 |
| Maslack Digital Ltd | Wholesale & retail | 2024 |
| Maslia Ltd | Hospitality | 2025 |
| Maslow Hunter Ltd | Administrative & support | 2015 |
| Mason and Sienna Harkus Property Management Ltd | Real estate | 2019 |
| Mason CE Financial Limited | Professional & scientific | 2013 |
| Mason Dynamics Ltd | Professional & scientific | 2024 |
| Mason Facades Ltd | Construction | 2018 |
| Mason Hamilton Ltd | Administrative & support | 2019 |
| Mason Marble & Granite Limited | Construction | 2007 |
| Mason Waste Management Ltd | Water & waste | 2024 |
| Mason's Auto Repairs Ltd | Wholesale & retail | 2013 |
| Masonlake Limited | Health & social care | 2016 |
| Masonoak Limited | Health & social care | 2009 |
| Masonworth Limited | Health & social care | 2010 |
| Masque London Ltd | Wholesale & retail | 2016 |
| Masroc Properties Limited | Real estate | 2018 |
| Mass Attention Ltd | Professional & scientific | 2019 |
| Mass Financial Corporation Ltd | Other services | 2019 |
| Mass Vending Ltd | Administrative & support | 2024 |
| Massab Mart Ltd | Wholesale & retail | 2026 |
| Massage Training Academy Ltd | Education | 2019 |
| Massala Exotic Limited | Hospitality | 2008 |
| Massay Investment Ltd | Other services | 2023 |
| Massmelt Limited | Professional & scientific | 2006 |
| Masster Fitness Ltd | Arts & recreation | 2020 |
| Mastach Communication Limited | Manufacturing | 2012 |
| Mastan Properties Limited | Real estate | 2025 |
| Master Agents Limited | Administrative & support | 2014 |
| Master Ball Cards Ltd | Wholesale & retail | 2024 |
| Master Carpet Cleaning Cardiff Ltd | Administrative & support | 2020 |
| Master ECN Limited | Information & communication | 2017 |
| Master Electrical Installations Ltd | Construction | 2012 |
| Master Frozen Ltd | Wholesale & retail | 2013 |
| Master Grill Express Ltd | Wholesale & retail | 2025 |
| Master Homes and Developments Ltd | Construction | 2018 |
| Master Learn Ltd | Professional & scientific | 2024 |
| Master Maintenance Ltd | Administrative & support | 2012 |
| Master N Company Ltd | Construction | 2025 |
| Master of Franchise Limited | Wholesale & retail | 2018 |
| Master Sports Massage & Therapy Ltd | Arts & recreation | 2024 |
| Master Taverns Limited | | 1991 |
| Master Tech Industries Limited | Information & communication | 2011 |
| Master Tutors Limited | Education | 2016 |
| Masterel Group Fabric and Textile Trading Limited | Wholesale & retail | 2025 |
| Masterfixtools Ltd | Wholesale & retail | 2025 |