| Marson Delivery Advisory Limited | Professional & scientific | 2026 |
| Marston Enterprises Limited | Financial services | 2011 |
| Marston-Willow Limited | Administrative & support | 2012 |
| Marth Brae Limited | Wholesale & retail | 2023 |
| Martin & Gerard Electrical Contractors Limited | Construction | 1983 |
| Martin Harris Limited | Health & social care | 2013 |
| Martinez Limited | Extraterritorial | 2026 |
| Marton CUM Grafton Property Co. Ltd | Construction | 2020 |
| Mary Page Limited | Hospitality | 2011 |
| Masala Takeaway Harrogate Limited | Hospitality | 2025 |
| Masculinity Limited | Extraterritorial | 2025 |
| Masenga Ltd | Transport & logistics | 2025 |
| Masham Properties Limited | Real estate | 2004 |
| Masicorp UK Ltd. | Education | 2009 |
| Mason Bennett Studio Ltd | Construction | 2025 |
| Mason Kelly Properties Ltd | Real estate | 2020 |
| Massalla Ltd | Extraterritorial | 2012 |
| Massive Architecture Ltd | Professional & scientific | 2022 |
| Master Distributor Limited | Wholesale & retail | 2009 |
| Mastiff Limited | Extraterritorial | 2026 |
| Matador Construction Limited | Financial services | 2018 |
| Matahala Ltd | Transport & logistics | 2020 |
| Materials Suppliers Ltd | Wholesale & retail | 2024 |
| Mato Holdings Ltd | Financial services | 2026 |
| MATR1X Ltd | Extraterritorial | 2020 |
| Matt Garner UK Ltd | Administrative & support | 2014 |
| Matt Malone Ltd | Health & social care | 2025 |
| Matt Sullivan Limited | Manufacturing | 2016 |
| Matt Urchin Limited | Arts & recreation | 2013 |
| Mattari Ltd | Wholesale & retail | 2025 |
| Matthew Dalton (Holdings) Limited | Financial services | 1989 |
| Matthew Peacock Media Ltd | Information & communication | 2023 |
| Matthew Swain Limited | Professional & scientific | 2014 |
| Mattlu Limited | Construction | 2014 |
| Matty Mortgage MAN Limited | Financial services | 2023 |
| MAX Box Limited | Real estate | 2006 |
| MAX Extra Limited | Wholesale & retail | 2025 |
| MAX Sterling Limited | Extraterritorial | 2012 |
| Maxim Developments Limited | Extraterritorial | 2025 |
| Maxim FM Limited | Extraterritorial | 2025 |
| Maximum Strength Limited | Extraterritorial | 2011 |
| Maxsub Ltd | Information & communication | 2025 |
| Maxwell Capital Limited | Extraterritorial | 2026 |
| Maxwell FM Limited | Extraterritorial | 2026 |
| MAY One Design Architecture Project Management Limited | Professional & scientific | 2013 |
| Mayfield Franklin Harrogate Ltd | Households | 2018 |
| Mazaya Al-Khashda Modern Trading Ltd | Wholesale & retail | 2025 |
| Mazel Commercial Ltd | Real estate | 2020 |
| Mazzarri Limited | Extraterritorial | 2026 |
| MB Harrogate Ltd | Hospitality | 2025 |
| MB House of Hair Limited | Arts & recreation | 2018 |
| MB Medical Device Consulting Limited | Administrative & support | 2020 |
| MB Pancake House Ltd | Hospitality | 2023 |
| MBA Estates (Kent) Limited | Other services | 2022 |
| MBC Repairs Limited | Manufacturing | 2023 |
| MC Optical Ltd | Manufacturing | 2004 |
| MC Top Nails Ltd | Other services | 2025 |
| MCB Homes Ltd | Real estate | 2024 |
| Mccardle Ltd | Professional & scientific | 2023 |
| Mcclure and Company Limited | Households | 2012 |
| Mccormicks Solicitors Limited | Extraterritorial | 2010 |
| Mcdowell Event Managment Ltd | Extraterritorial | 2010 |
| Mcevoy Holdings Ltd | Financial services | 2020 |
| Mcglashan Heating and Plumbing Ltd | Construction | 2020 |
| Mckenna Consultants Limited | Information & communication | 2004 |
| MCL Commercials Ltd | Extraterritorial | 2023 |
| MCL Solutions Limited | Mining & quarrying | 2011 |
| Mcmed Ltd | Manufacturing | 2019 |
| Mcmeekengale Ltd | Real estate | 2020 |
| Mcmorrow Murphy Limited | Financial services | 1977 |
| Mcnicholas Architects Ltd | Professional & scientific | 2014 |
| MCP Projects Ltd | Real estate | 2017 |
| Mcpg Developments Limited | Construction | 2021 |
| Mdav Events Ltd | Arts & recreation | 2026 |
| MDH 1 Limited | Hospitality | 2025 |
| MDR Motors Limited | Wholesale & retail | 2006 |
| MDY 2 Limited | Hospitality | 2025 |
| ME Parker Holdings Limited | Financial services | 2019 |
| Meadeway Information Works Limited | Information & communication | 2015 |
| Meadgate Medical Communications Ltd | Administrative & support | 2017 |
| Meadows & Turner Building Compliance Ltd | Administrative & support | 2026 |
| Meanwood Corporate Ventures Limited | Administrative & support | 2017 |
| Measurement Ltd | Professional & scientific | 2019 |
| Med-A-Data Ltd | Information & communication | 2018 |
| Media FM Limited | Extraterritorial | 2016 |
| Medical Neglect Limited | Wholesale & retail | 2021 |
| Medicinal Limited | Extraterritorial | 2012 |
| Mediocre Limited | Extraterritorial | 2012 |
| Medoc Limited | Wholesale & retail | 2025 |
| Medoh Ltd | Information & communication | 2025 |
| Medusa Holdings Limited | Extraterritorial | 2013 |
| Meet.Mba Limited | Administrative & support | 2018 |
| MEG Treherne Designs Limited | Professional & scientific | 2011 |
| MEG4N Limited | Extraterritorial | 2018 |
| MEL (Holdings) Limited | Professional & scientific | 2011 |
| MEL Anaesthetic Services Ltd | Health & social care | 2016 |
| MEL Environmental Solutions Limited | Water & waste | 2011 |
| MEL1SSA Limited | Extraterritorial | 2020 |
| MELAN1A Limited | Extraterritorial | 2020 |
| MELAN1E Ltd | Extraterritorial | 2020 |