| Martin Slowe | Professional & scientific | 1975 |
| Martin Slowe Property Investments Limited | Real estate | 2007 |
| Martin Slowe Property Services Limited | Real estate | 1975 |
| Martin Stabin Limited | Real estate | 1985 |
| Martina Jade Ltd | Administrative & support | 2012 |
| Martinelli Architecture Design Limited | Professional & scientific | 2011 |
| Martinez Group Limited | Professional & scientific | 2022 |
| Martingale Services Limited | Administrative & support | 2015 |
| Martins Electrical Services Ltd | Construction | 2015 |
| Martins Health Limited | Health & social care | 2016 |
| Martiva Management Ltd | Households | 2022 |
| Marvel Media Consultancy Ltd | Professional & scientific | 2017 |
| Mary Beauty & Hairstyles Ltd | Other services | 2022 |
| Marylebone Finco Limited | Real estate | 2016 |
| Marylebone Lane GP Co Limited | Real estate | 2016 |
| Marylebone Lane Income Co Limited | Real estate | 2016 |
| Marylebone Lane Nominee Co Limited | Administrative & support | 2016 |
| Marylin Services Ltd | Administrative & support | 2017 |
| Mary’S Care Ltd | Health & social care | 2017 |
| Masada Portfolio Limited | Professional & scientific | 2023 |
| Masala Creations Limited | Hospitality | 2012 |
| Mask LDN Ltd | Wholesale & retail | 2019 |
| Masons Coach Hire Limited | Transport & logistics | 2013 |
| Mast Export Packing Services Limited | Transport & logistics | 1998 |
| Master Construction Development Limited | Construction | 2022 |
| Master Gatto Ltd | Construction | 2021 |
| Master Music Publications Ltd | Information & communication | 2018 |
| Masterson Developments Limited | Construction | 2019 |
| Masterson Holdings Limited | Professional & scientific | 2001 |
| Mat-Ice 1994 UK Ltd | Wholesale & retail | 2025 |
| Matalin Limited | Administrative & support | 1992 |
| Matrix Design & Build Limited | Construction | 2012 |
| Maudata Limited | Information & communication | 2024 |
| Mava Properties Ltd | Real estate | 2023 |
| MAX GD Ltd | Construction | 2023 |
| Maxdeko Ltd | Wholesale & retail | 2024 |
| Maxmar Ltd | Transport & logistics | 2024 |
| Maxshelf Limited | Wholesale & retail | 2008 |
| Maxshelf Retail Shelving Solutions Ltd | Wholesale & retail | 2020 |
| Maxtekk Ltd | Wholesale & retail | 2026 |
| Maxwell Fine Studio Ltd | Professional & scientific | 2018 |
| Maxxem Ltd | Construction | 2011 |
| MAY Gardens Management Company Limited | Households | 1997 |
| MAY the Best MAN WIN Films Limited | Arts & recreation | 2013 |
| Mayara Ltd | Administrative & support | 2016 |
| Maybridge Reserve Ltd | Administrative & support | 2026 |
| Mayfair Harley Clinic Ltd | Health & social care | 2019 |
| Mayfair Management and Concierge Limited | Real estate | 2020 |
| Mayfair Wealth Management Limited | Professional & scientific | 2010 |
| Mayfield Hospitality Limited | Hospitality | 2016 |
| Mayfield Hospitality Properties Limited | Hospitality | 2020 |
| Mayflower Capital Limited | Financial services | 2016 |
| Mayope Limited | Manufacturing | 2025 |
| Maytiv Ltd | Real estate | 2024 |
| Maytree Court (Hadley Wood) Management Company Limited | Households | 2019 |
| Mayvee Group Limited | Professional & scientific | 2018 |
| MAZ Enterprize Ltd | Real estate | 2021 |
| MB Builders and Contractors Ltd | Construction | 2016 |
| MB CB Britain Limited | Financial services | 2025 |
| MB CB London Limited | Financial services | 2025 |
| MB CB Online Limited | Financial services | 2025 |
| MBC Enterprises Limited | Information & communication | 2004 |
| MBC Financial Limited | Financial services | 2016 |
| MBH Finco. Limited | Real estate | 2013 |
| MBS Bathroom & Kitchen Limited | Wholesale & retail | 2016 |
| MBS Building and Property Services Limited | Construction | 2019 |
| MBS Rapidez Limited | Hospitality | 2019 |
| Mbsh Services Film and TV Ltd | Administrative & support | 2023 |
| MC Advice Ltd | Administrative & support | 2020 |
| MC Consulting Services Limited | Other services | 2019 |
| MC Jewellery Ltd | Wholesale & retail | 2025 |
| MC Pipelines Ltd | Construction | 2016 |
| Mc.Renovation Ltd | Real estate | 2021 |
| Mcbull Limited | Construction | 2019 |
| Mccaffertys PUB Co Ltd | Hospitality | 2026 |
| MCH Property Investment Ltd | Real estate | 2017 |
| MCI Investments Ltd | Extraterritorial | 2009 |
| Mclaren Private Office Ltd | Professional & scientific | 2018 |
| MCM Network Limited | Construction | 2022 |
| MCM Wedding Services Ltd | Other services | 2021 |
| Mcmullen Facades Limited | Manufacturing | 2017 |
| Mcnamara Property Norfolk Limited | Construction | 2021 |
| MCR Dens Management Ltd | Real estate | 2023 |
| Mctague Inc Ltd | Arts & recreation | 2025 |
| MD Labx Limited | Administrative & support | 2025 |
| MD. Dimitrov Construction Ltd | Construction | 2022 |
| MDC Rail Ltd | Construction | 2019 |
| Mddynamics Ltd | Real estate | 2021 |
| MDN Management Ltd | Professional & scientific | 2023 |
| MDR RDR Holdings Limited | Professional & scientific | 2016 |
| MDS (Exeter) Ltd | Construction | 2022 |
| MDS (Leeds) Ltd | Construction | 2021 |
| MDS (Manchester) Ltd | Construction | 2023 |
| MDS (Nottingham 2022) Ltd | Construction | 2022 |
| MDS (Nottingham) Ltd | Construction | 2021 |
| MDS Removals & Storage Ltd | Transport & logistics | 2018 |
| Mdware Limited | Information & communication | 2013 |
| ME Love Events Ltd | Arts & recreation | 2020 |
| Meadacre Limited | Professional & scientific | 2025 |
| Meadow Computing Limited | Information & communication | 2015 |