| LW Real Estate Limited | Real estate | 2019 |
| LWE Flooring Ltd | Construction | 2022 |
| M & G Property Development Limited | Real estate | 2019 |
| M a Hitchcock Roofing Limited | Construction | 2017 |
| M Herring Plumbing & Heating Limited | Construction | 2017 |
| M J Muscroft Ltd | Health & social care | 2022 |
| M Management Ltd | Real estate | 2016 |
| M P a Limited | Professional & scientific | 2006 |
| M R Gadget Services Limited | Wholesale & retail | 2021 |
| M S Hire Ltd | Information & communication | 2010 |
| M&M Gift Shop Ltd | Wholesale & retail | 2025 |
| M.A.T Imports Ltd | Manufacturing | 2015 |
| M.H.Bros Limited | Hospitality | 2024 |
| M.L. Magowan Ltd | Administrative & support | 2026 |
| Mabans Consultancy Ltd | Professional & scientific | 2019 |
| MAC Constructions and Services Ltd | Construction | 2025 |
| MAC Group Investments Ltd | Real estate | 2025 |
| Macagro Ltd | Professional & scientific | 2023 |
| Macevoy Consulting Limited | Information & communication | 2014 |
| Macz Consulting Limited | Professional & scientific | 2017 |
| Mada Green Cleaning Services Ltd | Administrative & support | 2025 |
| Made in Africa Coffee Company Limited | Manufacturing | 2026 |
| Made in ST Margaret's Limited | Wholesale & retail | 2017 |
| Made Kind Ltd | Wholesale & retail | 2020 |
| Madinah Way Ltd | Wholesale & retail | 2021 |
| Madingley Court Residents Management Limited | Hospitality | 1986 |
| Madnet Training 2025 Ltd | Administrative & support | 2025 |
| Maestro Music Learning Ltd | Education | 2024 |
| MAF IT Limited | Information & communication | 2011 |
| Maflux Ltd | Professional & scientific | 2013 |
| Maggie MAY London Ltd | Wholesale & retail | 2021 |
| MAIDENSTAYS360 Ltd | Real estate | 2026 |
| Maintenance Lupsa Limited | Manufacturing | 2020 |
| Maircon Ltd | Information & communication | 2012 |
| Mairlot Consulting Limited | Professional & scientific | 2016 |
| Mairéad Murray Media Ltd | Administrative & support | 2013 |
| Majestic Gallery Ltd | Wholesale & retail | 2026 |
| Makan-Makan Limited | Hospitality | 2020 |
| Makauda Ltd | Professional & scientific | 2026 |
| Makealeap Ltd | Professional & scientific | 2008 |
| Mala Ecom Limited | Wholesale & retail | 2025 |
| Malesori Ltd | Construction | 2025 |
| Mall School Trust(The) | Education | 1986 |
| Malmesbury Abbey Stable Apartments (Masa) Limited | Households | 1999 |
| MAM Capital Partners Ltd | Extraterritorial | 2016 |
| MAM Partner Plus Limited | Information & communication | 2025 |
| Mammoth Graphics Limited | Information & communication | 2006 |
| MAN CUB Limited | Professional & scientific | 2014 |
| Manageaid Software Solutions Ltd | Information & communication | 2021 |
| Mandarin Ducklings Education Limited | Education | 2013 |
| Mango Airport Cars Ltd | Transport & logistics | 2019 |
| Mani & Mani Ltd | Financial services | 2024 |
| Manocha & Sons Ltd | Wholesale & retail | 2020 |
| Manoo Ltd | Hospitality | 2019 |
| Mantu Properties Limited | Households | 2022 |
| Maple Branch Ltd | Manufacturing | 2022 |
| Maplecrest Properties UK Ltd | Construction | 2025 |
| MAQ Property Services Ltd | Real estate | 2026 |
| MAR 2021 Ltd | Transport & logistics | 2021 |
| Mara BI Ltd | Hospitality | 2020 |
| Marble Hill Playcentres | Arts & recreation | 2001 |
| Marc Homes Limited | Information & communication | 2017 |
| Marcill Limited | Professional & scientific | 2025 |
| Margate Sands Limited | Information & communication | 2017 |
| Marianna Wilford Interiors Limited | Professional & scientific | 2006 |
| Mario & B Construction Ltd | Construction | 2017 |
| Mark Edwards Services Ltd | Construction | 2013 |
| Mark Langston Limited | Professional & scientific | 2023 |
| Mark Lettings Limited | Real estate | 2024 |
| Mark R Johnson Limited | Professional & scientific | 2024 |
| Marlow Photographic & Investments Ltd | Wholesale & retail | 2021 |
| Mars Energy Limited | Energy | 2023 |
| Marsh Puremia Ecommerce Limited | Wholesale & retail | 2026 |
| Marsh Puremia Property Limited | Real estate | 2017 |
| Marshall Cardiology Ltd | Health & social care | 2024 |
| Martechbase Ltd | Information & communication | 2025 |
| Martyn Hayes Productions Ltd | Arts & recreation | 2012 |
| Martyr's Lane Ltd | Information & communication | 2016 |
| Masaniello Restaurant Limited | Hospitality | 2015 |
| Mason and Dale Recruitment Ltd | Administrative & support | 2020 |
| Mason Woodard Limited | Professional & scientific | 2003 |
| Masterkraft Builders Ltd | Construction | 2023 |
| Math Arts and Brands Limited | Professional & scientific | 2015 |
| Mathern Properties LLP | | 2017 |
| Matrix 2021 Bidco Limited | Financial services | 2021 |
| Matrix 2021 Holdings Limited | Financial services | 2023 |
| Matrix 2021 Midco 1 Limited | Financial services | 2021 |
| Matrix 2021 Midco 2 Limited | Financial services | 2021 |
| Matrix 2021 Topco Limited | Financial services | 2021 |
| Matt Lipsey Limited | Information & communication | 2004 |
| Matt Usher Strategy Consulting Ltd | Professional & scientific | 2020 |
| Matthew Frank Gould Ltd | Arts & recreation | 2011 |
| Mattiavelli Investments Limited | Real estate | 2024 |
| MAX Motus Ltd | Transport & logistics | 2022 |
| MAX Smith Golf Ltd | Arts & recreation | 2025 |
| Maximilian Kilman Management Ltd | Professional & scientific | 2022 |
| Maxsimafoto Limited | Wholesale & retail | 2013 |
| Mayer & Mayer Limited | Manufacturing | 2011 |
| Mayfair Property Concierge Services Limited | Households | 2025 |
| Mayford Preschool Limited | Education | 2018 |