| Maximum Energy Ltd | Construction | 2026 |
| MAY Styles Limited | Other services | 2003 |
| Mayne Vision Limited | Wholesale & retail | 2001 |
| Mayura Academy Limited | Education | 2016 |
| Mayura Yoga Limited | Other services | 2013 |
| MAZ Developments Limited | Real estate | 2002 |
| MB Design & Surveyors Ltd | Professional & scientific | 2013 |
| MBC Cars Limited | Other services | 2014 |
| MC Carthy Projects Ltd | Construction | 2003 |
| Mcaloren Construction Limited | Real estate | 2011 |
| Mccapp Holdings Ltd | Administrative & support | 2017 |
| Mccarthy Peters Construction Limited | Construction | 2015 |
| Mcgowan Landscapes & Garden Services Ltd | Administrative & support | 2025 |
| MCL Construction Services Ltd | Construction | 2019 |
| MCL Housing Ltd | Real estate | 2022 |
| Mcnamee Holdings Limited | Financial services | 2025 |
| Mcnamee Properties Limited | Real estate | 2025 |
| Mcski Consulting Limited | Professional & scientific | 2014 |
| MD Leadership Coaching Ltd | Professional & scientific | 2015 |
| MDF Catering Ltd | Wholesale & retail | 2020 |
| MDF Consultancy Ltd | Transport & logistics | 2018 |
| Mdlco Ltd | Construction | 2025 |
| MDR Carpentry and Property Services Ltd | Administrative & support | 2015 |
| Meamo Ltd | Wholesale & retail | 2018 |
| Measurement & Prosper Ltd | Professional & scientific | 2022 |
| Mech ENG Serv Ltd | Professional & scientific | 2025 |
| Mechex Global Limited | Administrative & support | 2025 |
| Mechflo Ltd | Construction | 2025 |
| Meco Capital Limited | Real estate | 2025 |
| Medifat Limited | Health & social care | 2013 |
| Medin Care Services Limited | Health & social care | 2016 |
| Medizone Limited | Health & social care | 2015 |
| Meech Consulting Ltd | Wholesale & retail | 2021 |
| Megabug Limited | Manufacturing | 2002 |
| Melbid Construction Limited | Construction | 2001 |
| Meme the Brand Limited | Wholesale & retail | 2026 |
| Memstars Ltd | Wholesale & retail | 2025 |
| Men's Fit Club Ltd | Other services | 2023 |
| MEP Networks Ltd | Manufacturing | 2026 |
| Mercatech Ltd | Professional & scientific | 2024 |
| Mercury Heating Limited | Construction | 1999 |
| Merit Solutions Limited | Administrative & support | 2016 |
| Merrynevs Properties Limited | Real estate | 2018 |
| Meteortrail Ltd | Information & communication | 2025 |
| Method DC Limited | Other services | 2007 |
| Meyrin House Development Ltd | Real estate | 2021 |
| MF Kitchen Installations Ltd | Administrative & support | 2017 |
| MFS Lettings Ltd | Real estate | 2023 |
| MGH Building Solutions Limited | Construction | 2013 |
| MH Construction and Interiors Ltd | Construction | 2026 |
| Mhelectricalmechanical Ltd | Construction | 2025 |
| MIB Global Limited | Information & communication | 2020 |
| Micandav Ltd | Health & social care | 2022 |
| Microma Leisure Limited | Construction | 1998 |
| Micropet Limited | Administrative & support | 2019 |
| Middas Limited | Hospitality | 2000 |
| Middlesmith Limited | Professional & scientific | 2018 |
| Mihrisah Apparel UK Limited | Wholesale & retail | 2020 |
| Mike's Health Limited | Other services | 2013 |
| Millsdon Catering Limited | Hospitality | 2025 |
| Milt-Tec Limited | Information & communication | 2002 |
| Minds Education Ltd | Education | 2024 |
| Mini Dolls Boutique Ltd | Wholesale & retail | 2018 |
| Mini Meadow Ltd | Real estate | 2023 |
| MIO Software Ltd | Information & communication | 2021 |
| Miura Financial Solutions Ltd | Financial services | 2010 |
| MJ Adsystems Ltd | Professional & scientific | 2026 |
| MJF Property Developments Ltd | Real estate | 2026 |
| MJG Business & Office Support Solutions Limited | Administrative & support | 2013 |
| Mjjp Consulting Limited | Professional & scientific | 2018 |
| Mjkc Electrical Limited | Construction | 2012 |
| MJS Scenic Painting and Decorating Ltd | Construction | 2026 |
| MK & Sons Ltd | Transport & logistics | 2011 |
| MK CAD Services Limited | Professional & scientific | 2014 |
| MK Training Academy Ltd | Education | 2022 |
| Mkgl Holdings Limited | Financial services | 2025 |
| MKK Flooring Limited | Construction | 2015 |
| MKS Coaching Ltd | Education | 2025 |
| Mksa Investments Limited | Real estate | 2022 |
| ML Assets Ltd | Arts & recreation | 2021 |
| MLB Contractors Limited | Construction | 2024 |
| MLR Tooling (Essex) Limited | Other services | 2024 |
| MM (South East) Ltd | Construction | 2019 |
| MM Solar Ltd | Energy | 2023 |
| MMA Groundwork Limited | Other services | 2010 |
| MNH Medical Services Ltd | Health & social care | 2013 |
| MNJ Mechanical Services Ltd | Construction | 2015 |
| MO Building Solutions Limited | Construction | 2014 |
| Modelia Group Ltd | Information & communication | 2023 |
| Modern Specialised Render Ltd | Construction | 2018 |
| Moji Entertainer Ltd | Arts & recreation | 2022 |
| Moji Entertainment Limited | Arts & recreation | 2026 |
| Moments of Time Limited | Wholesale & retail | 2019 |
| Monaghan Utility Services Ltd | Construction | 2025 |
| Monster Parties Trade Limited | Wholesale & retail | 2014 |
| Montabonel & Partners Limited | Other services | 2014 |
| Montage Media Ltd | Information & communication | 2022 |
| Moonstar Developments Limited | Construction | 2018 |
| Moore AP Limited | Professional & scientific | 2001 |
| Moore Stephens Azerbaijan Limited | Professional & scientific | 2001 |