| Marlin Heating Systems Limited | Energy | 2005 |
| Marmalade Media Limited | Other services | 2011 |
| Marner Transit Limited | Transport & logistics | 2026 |
| Maroush Store Limited | Wholesale & retail | 2024 |
| Marrie Ltd | Wholesale & retail | 2025 |
| Mars Driving School Ltd | Education | 2022 |
| Marsh Parade Superstore Limited | Wholesale & retail | 2018 |
| Marshallmaps Limited | Professional & scientific | 2020 |
| Marshborne Limited | Other services | 2023 |
| Marshcroft Technology Limited | Professional & scientific | 2025 |
| Marston Manors Limited | Real estate | 2015 |
| Martal Properties Limited | Real estate | 2016 |
| Maruti Transport Ltd | Transport & logistics | 2014 |
| MARVAL75 Ltd | Transport & logistics | 2017 |
| Marvito Services Limited | Construction | 2023 |
| Mary Gregory Limited | Professional & scientific | 2016 |
| Marynas Electrical & Electronic Services Ltd | Manufacturing | 2019 |
| Masab Awais Ltd | Wholesale & retail | 2023 |
| Masi Property Ltd | Real estate | 2020 |
| Mason Property Development Company Limited | Real estate | 2001 |
| Massacre Sounds Limited | Arts & recreation | 2012 |
| Masson Developments Ltd | Construction | 2014 |
| Master Karate Club Ltd | Education | 2018 |
| Master Scenic Painter Ltd | Construction | 2011 |
| Master Way Joinery Ltd | Manufacturing | 2010 |
| Masters of Mindset Ltd | Administrative & support | 2020 |
| Mastershot Studios (UK) Ltd | Information & communication | 2026 |
| Masterwork Renovations Ltd | Manufacturing | 2026 |
| Matcha Mist Ltd | Manufacturing | 2025 |
| Matcha Run Ltd | Wholesale & retail | 2024 |
| Matissa Ltd | Wholesale & retail | 2013 |
| Matko&Co Ltd | Wholesale & retail | 2026 |
| Matrix Builders Ltd | Construction | 2020 |
| Matrix Surveys Limited | Professional & scientific | 1996 |
| Matt & Brad Properties Limited | Real estate | 2021 |
| Matt Webb Services Ltd | Arts & recreation | 2018 |
| Matters of the Mind Ltd | Health & social care | 2012 |
| Matterstack Ltd | Information & communication | 2026 |
| Matti Properties Ltd | Real estate | 2015 |
| Maviro Ltd | Information & communication | 2025 |
| MAX GAS Heating Ltd | Construction | 2015 |
| Maxicon Ltd | Arts & recreation | 2015 |
| Maya Dahlia Cakes Limited | Wholesale & retail | 2014 |
| Maybax Fittings Limited | Other services | 2025 |
| Maycrest Ltd | Real estate | 2019 |
| Mayfair Homes Investments Ltd | Real estate | 2020 |
| Mayfair Lighting Ltd | Information & communication | 2021 |
| Mayleigh Properties Limited | Real estate | 2010 |
| Mayn Limited | Information & communication | 2011 |
| Maynard Court (Staines) Residents Association Limited | Real estate | 1986 |
| Mayura Ziani Limited | Financial services | 2025 |
| Mayuu SID Ltd | Wholesale & retail | 2025 |
| Mazadar Limited | Hospitality | 2026 |
| Mazaru Limited | Information & communication | 1989 |
| MB Idrees Productions Ltd | Information & communication | 2026 |
| MB Photography Limited | Professional & scientific | 2018 |
| MB UK Investment Ltd | Real estate | 2023 |
| Mb-Surgical Ltd | Health & social care | 2022 |
| Mbcmaintaince Ltd | Construction | 2015 |
| MBJ Project Limited | Construction | 2016 |
| MBM Waste Limited | Water & waste | 2018 |
| MBN Homes Ltd | Real estate | 2023 |
| MBN Property Ltd | Administrative & support | 2019 |
| Mbos London Ltd | Wholesale & retail | 2018 |
| MC Cleaning London Ltd | Administrative & support | 2025 |
| Mcass Limited | Information & communication | 2014 |
| Mcbride Collective Ltd | Information & communication | 2025 |
| Mccarthy Electrical Limited | Construction | 2015 |
| MCD Consulting Services Limited | Professional & scientific | 2025 |
| Mcelroy Scenery Ltd | Construction | 2025 |
| MCG Education Limited | Administrative & support | 2016 |
| MCG Group (Training) Limited | Financial services | 2021 |
| MCG Spare Limited | Extraterritorial | 2018 |
| Mcgill (UK) Limited | Professional & scientific | 2007 |
| Mcgill Engineering Services Limited | Manufacturing | 2011 |
| Mcjoy Limited | Health & social care | 2016 |
| Mckedis Enterprises Ltd | Professional & scientific | 2025 |
| Mclaren Specter Litt Limited | Real estate | 2019 |
| Mclaughlin Holdings Limited | Financial services | 2018 |
| Mclaughlin Investments Limited | Real estate | 2018 |
| Mcmj Handyman Ltd | Construction | 2019 |
| MCP Asset Management 1 Ltd | Real estate | 2021 |
| MCS Control Systems Limited | Manufacturing | 1976 |
| MCS Worlwide Limited | Transport & logistics | 2016 |
| MD Dental Laboratories Ltd | Health & social care | 2016 |
| MD Events Promotion Ltd | Other services | 2014 |
| MD Limitada Limited | Wholesale & retail | 2019 |
| MD Roofing & Construction Ltd | Construction | 2024 |
| MDA Construction Group Ltd | Construction | 2019 |
| MDF7 Ltd | Wholesale & retail | 2023 |
| MDH IT Consultancy Limited | Information & communication | 2010 |
| MDJ Osteomed Ltd | Health & social care | 2018 |
| Mdja Ltd | Professional & scientific | 2023 |
| Mdjr Beauty Ltd | Other services | 2026 |
| MDM Traders Ltd | Administrative & support | 2013 |
| MDN SP101 Ltd | Real estate | 2024 |
| MDR Build Ltd | Construction | 2019 |
| Meadowbrook Ltd | Administrative & support | 2016 |
| Meadowlight Support Care Ltd | Health & social care | 2025 |
| Meadows Residents Association Limited(The) | Extraterritorial | 1980 |