| Macavy Ltd | Real estate | 2024 |
| Macc Property Ltd | Construction | 2013 |
| Macdonald Design Engineering Ltd. | Manufacturing | 2010 |
| Machines for Humans Ltd | Wholesale & retail | 2023 |
| Mack Missions Ltd | Transport & logistics | 2020 |
| Macnath Limited | Real estate | 2019 |
| Madeira Court (ST Johns) Limited | Households | 2002 |
| Madeira Services Ltd | Transport & logistics | 2022 |
| Madewell Productions Limited | Professional & scientific | 2015 |
| Magiamore Limited | Manufacturing | 2026 |
| Magic Splash Swim School Ltd | Education | 2026 |
| Magictouch Properties Ltd | Real estate | 2023 |
| Magictouch Solutions Ltd | Information & communication | 2009 |
| Magna Management Services Limited | Real estate | 2003 |
| Maidenhead Sushi Ltd | Hospitality | 2024 |
| Mail and Print Limited | Manufacturing | 2006 |
| Mainline Day Nursery and PRE School Ltd | Education | 2016 |
| Mainspring Watches UK Ltd | Wholesale & retail | 2021 |
| Maiora Spirits Ltd | Manufacturing | 2023 |
| MAK Comms Ltd | Professional & scientific | 2021 |
| Makaw Studio Ltd | Wholesale & retail | 2026 |
| Make Maths Simple Ltd | Education | 2025 |
| Mallard Property Maintenance Ltd | Administrative & support | 2025 |
| Mama Lou’S Smokehouse & Grill Limited | Hospitality | 2021 |
| Mangrove Group Ltd | Financial services | 2022 |
| Manor Kitchens & Interiors Ltd | Construction | 2017 |
| Manorview Commercial Ltd | Real estate | 2024 |
| Maps Haulage Ltd | Transport & logistics | 2025 |
| Maps Investment Ltd | Other services | 2017 |
| Marben & Company UK Limited | Administrative & support | 2007 |
| Marben Services Ltd | Administrative & support | 2018 |
| Marble Construction Ltd | Construction | 2008 |
| Mariam Yussif Limited | Administrative & support | 2025 |
| Marian Infotech Ltd | Information & communication | 2022 |
| Marie Bruce Beauty Limited | Other services | 2019 |
| Mark Liddle Flooring Limited | Administrative & support | 2006 |
| Mark Mullins MAN and a Van Ltd | Extraterritorial | 2017 |
| Mark Transport Company Limited | Wholesale & retail | 1973 |
| Marli Construction Limited | Construction | 2019 |
| Marrowbrook Limited | Real estate | 2020 |
| Martin & Simon Maintenance Limited | Construction | 2022 |
| Martin Care Services Ltd | Health & social care | 2011 |
| Martops Consulting Ltd | Professional & scientific | 2023 |
| Mase Properties Ltd | Real estate | 2013 |
| Masian Ltd | Other services | 2011 |
| Massel UK Limited | Manufacturing | 2017 |
| Massey Technology Limited | Information & communication | 2016 |
| Master Bites UK Ltd | Wholesale & retail | 2024 |
| Mastery Education Ltd | Education | 2022 |
| Materion UK Limited | Manufacturing | 2009 |
| Matheos-Lic Ltd | Health & social care | 2022 |
| Matheson's Roofing Company Limited | Construction | 2022 |
| Matrix Electrical Ltd | Construction | 2022 |
| Matrix Service Development & Training Ltd | Health & social care | 1999 |
| Matt LEE Rigging Services Ltd | Manufacturing | 2015 |
| Matthews Direct Imports Ltd | Wholesale & retail | 2009 |
| Matthews Management Consultancy Ltd | Information & communication | 2021 |
| Maviada Limited | Wholesale & retail | 2016 |
| MAW Comms Ltd | Administrative & support | 2021 |
| Maxcare Day Centres Limited | Administrative & support | 2022 |
| Maxcare Ltd | Health & social care | 2012 |
| Maxparts Limited | Wholesale & retail | 1997 |
| Maxstan Services Ltd | Professional & scientific | 2022 |
| MAY Advice Services Ltd | Administrative & support | 2017 |
| Mazin AL Noor Ltd | Professional & scientific | 2019 |
| MB & CB Construction Ltd | Construction | 2026 |
| MB Building & Construction Limited | Construction | 2012 |
| Mb-Db IT Consulting Ltd | Information & communication | 2023 |
| MBE Ltd | Construction | 2018 |
| Mbts T/A MB Tree Services Ltd | Administrative & support | 2019 |
| MC Surveying Ltd | Professional & scientific | 2026 |
| Mccallion Services Limited | Arts & recreation | 2006 |
| Mcdonald Trading Network Ltd | Construction | 2024 |
| MCS (Farnborough) Ltd | Manufacturing | 2018 |
| Mcsj Limited | Professional & scientific | 2026 |
| MD & S Ltd | Real estate | 2023 |
| MD Property Portfolio Limited | Real estate | 2016 |
| MD Vehicle Solutions Limited | Wholesale & retail | 2011 |
| MD02 Kebab Ltd | Hospitality | 2023 |
| Mdadistribution Limited | Transport & logistics | 2026 |
| MDW Pest Control Ltd | Administrative & support | 2017 |
| Meadowbrook Montessori Limited | Education | 2015 |
| Mechanics and Welding Limited | Manufacturing | 2017 |
| Mechatech Design Limited | Professional & scientific | 2007 |
| Mechlabsuk Ltd | Wholesale & retail | 2026 |
| Medfor Products Limited | Manufacturing | 1999 |
| Mediaroute Ltd. | Administrative & support | 2020 |
| Mediation Specialists Limited | Administrative & support | 2010 |
| Medisign Ltd | Information & communication | 2012 |
| Mediso Medical Imaging Systems UK Limited | Manufacturing | 1998 |
| Medusa Vape Ltd | Wholesale & retail | 2022 |
| Meertec Limited | Professional & scientific | 2014 |
| Meesu Properties Limited | Real estate | 2024 |
| Melody Care Aldershot Ltd | Health & social care | 2016 |
| Melody Care Alton Ltd | Health & social care | 2015 |
| Melody Care Ltd | Health & social care | 2005 |
| Melowen Associates Ltd | Information & communication | 2026 |
| Melrose Bespoke Property Services Ltd | Construction | 2022 |
| Mentholatum (Overseas) Limited | Financial services | 1965 |
| Mentor Marketing Ltd | Administrative & support | 2010 |