| Marketing Bulls Ltd | Information & communication | 2024 |
| Marketing by Zubair Ltd | Professional & scientific | 2023 |
| Marketing Platform Solutions Ltd | Information & communication | 2025 |
| Markhor Property Development Ltd | Real estate | 2026 |
| Marl PVT Ltd | Construction | 2024 |
| Marlow Water Gardens Limited | Administrative & support | 2010 |
| Marlston Assets Ltd | Hospitality | 2023 |
| Marma Care Ltd | Health & social care | 2021 |
| Maroush Group Limited | Hospitality | 2012 |
| Maroush II Company Limited | Hospitality | 1989 |
| Marriam M Studio Ltd | Other services | 2025 |
| Marrium & Hamdan Ltd | Wholesale & retail | 2026 |
| Marrow Plant Services Ltd | Professional & scientific | 2025 |
| Marry Cons Ltd | Construction | 2025 |
| Mars Food UK Limited | Manufacturing | 2008 |
| Mars Horsecare UK Limited | Manufacturing | 1998 |
| Mars Installation and Cladding Limited | Construction | 2009 |
| Mars Pet Services UK Limited | Financial services | 2016 |
| Mars Petcare UK | Manufacturing | 2008 |
| Mars Petcare UK Holdings Limited | Professional & scientific | 2008 |
| Mars Peterborough UK Holdings Limited | Professional & scientific | 2010 |
| Mars Retail Services UK Limited | Professional & scientific | 2009 |
| Mars Trading UK Ltd | Wholesale & retail | 2020 |
| Mars Wrigley Confectionery UK Limited | Manufacturing | 2008 |
| Marsden Ventures Ltd | Administrative & support | 2007 |
| Marshal Remit Ltd | Financial services | 2016 |
| Marshall Traders Ltd | Administrative & support | 2021 |
| Marshalls Security Group Ltd | Administrative & support | 2016 |
| Marshell Transport Limited | Transport & logistics | 2024 |
| Martello Star Ltd | Real estate | 2022 |
| Martin Construction Building Ltd | Construction | 2024 |
| Martin Food Equipment Limited | Wholesale & retail | 2010 |
| Marv Capital LLP | | 2016 |
| Marvcaps Limited | Real estate | 2025 |
| Marvel Homes & Builders Ltd | Real estate | 2019 |
| Marvel Worldwide Services UK Ltd. | Transport & logistics | 2017 |
| Marvestyne Ltd | Professional & scientific | 2015 |
| Marwa and Sehdev Ltd | Hospitality | 2024 |
| Marwa Trading Limited | Wholesale & retail | 2004 |
| Mary Abey Care Ltd | Health & social care | 2018 |
| Mary's Guardians Ltd | Education | 2025 |
| Maryadi Limited | Education | 2013 |
| Maryfield West Care Limited | Health & social care | 2019 |
| Maryo Builders Ltd | Construction | 2019 |
| Maryside Realty Limited | Real estate | 2025 |
| Marzouk Surgery Ltd | Health & social care | 2025 |
| MAS Plumbing & Heating Services Ltd | Construction | 2025 |
| Masala Life Films Limited | Professional & scientific | 2024 |
| Masala N Munchies Limited | Hospitality | 2024 |
| Masaya Solutions Ltd | Information & communication | 2026 |
| Mascomms Ltd | Information & communication | 2019 |
| Maserati GB Limited | Administrative & support | 2005 |
| Mashandudze Services Ltd | Health & social care | 2025 |
| Maskan Investments Ltd | Real estate | 2020 |
| Masonview Homes Ltd | Construction | 2024 |
| Masood Halal Meat Limited | Wholesale & retail | 2022 |
| Masoom Sons Limited | Transport & logistics | 2021 |
| Mass Digital Limited | Information & communication | 2019 |
| Massage Services Ltd | Health & social care | 2023 |
| Massimo Trapani Ltd | Hospitality | 2017 |
| Master Builders Group Ltd | Construction | 2018 |
| Master Ceramics Ltd | Wholesale & retail | 2025 |
| Master D&A Group Ltd | Financial services | 2026 |
| Master FIX Roofing & Upvc Ltd | Construction | 2019 |
| Master Homes Ltd | Real estate | 2026 |
| Masterlift Construction Limited | Construction | 2014 |
| Masters of Impact Limited | Education | 2017 |
| Masterstrokespro Limited | Manufacturing | 2022 |
| Masy Engineers Ltd | Professional & scientific | 2023 |
| Masz Limited | Real estate | 2024 |
| MAT Property Development Limited | Real estate | 2024 |
| Match Frame Post Ltd | Professional & scientific | 2017 |
| Match Go Ltd | Administrative & support | 2026 |
| Match Options Franchising Ltd | Professional & scientific | 2011 |
| Match Options Ltd | Administrative & support | 2012 |
| Matcha People Ltd | Wholesale & retail | 2025 |
| Mate Enterprizes Ltd | Wholesale & retail | 2023 |
| Mateeno Ltd | Wholesale & retail | 2019 |
| Matefile Limited | Administrative & support | 2010 |
| Matex Energy Ltd | Mining & quarrying | 2023 |
| Mathew & Co Ltd | Education | 2013 |
| Mathias&Yanys Limited | Construction | 2023 |
| Mathnspire Classes Ltd | Education | 2019 |
| Maths Logistics UK Ltd | Wholesale & retail | 2024 |
| Matrix & SON Roofing Ltd | Construction | 2021 |
| Matrix Medical Materials Ltd | Manufacturing | 2024 |
| Matrix Plastics Limited | Manufacturing | 1991 |
| Matrix Sourcing Ltd | Wholesale & retail | 2023 |
| Matrix Staffing Solutions Limited | Administrative & support | 2024 |
| Matrix Visionary Ltd | Wholesale & retail | 2024 |
| Matrixgen Limited | Wholesale & retail | 2025 |
| Matt Design Ltd | Professional & scientific | 2014 |
| Matt Metal Ltd | Water & waste | 2014 |
| Mattel Entertainment Holdings Limited | Extraterritorial | 2011 |
| Mattel U.K. Limited | Wholesale & retail | 1980 |
| Mattel UK Holdings Limited | Professional & scientific | 2000 |
| Matthew Stirling Limited | Arts & recreation | 2010 |
| Mattock Lane Ltd | Construction | 2014 |
| Mattu Property Holding Limited | Real estate | 2026 |
| Maturing Naturally Younger Ltd | Other services | 2023 |