| Marktech & Co Ltd | Professional & scientific | 2025 |
| Mary ANN Weeks (Walton) Limited | Other services | 2008 |
| Marymarc Limited | Hospitality | 2005 |
| Mashplant Media Ltd | Information & communication | 2017 |
| Massanz Energy Ltd | Wholesale & retail | 2026 |
| Master Reset Consultancy Group Limited | Professional & scientific | 2025 |
| Masterpiece Construction Ltd | Construction | 2023 |
| Matrixx Holdings Ltd | Construction | 2025 |
| Matrixx Limited | Construction | 2023 |
| Maven Intelligent Solutions Ltd | Manufacturing | 2019 |
| Maverick Bear Entertainment Ltd | Information & communication | 2024 |
| Maya DEL Ltd | Professional & scientific | 2024 |
| Maybella.Hb Limited | Other services | 2025 |
| Mayel Software Solutions Ltd | Information & communication | 2018 |
| Mayfair Plant Hire Ltd | Administrative & support | 2019 |
| Mayfair Waste Management Ltd | Water & waste | 2020 |
| Mayhew Property Care Limited | Other services | 2002 |
| Mayormedical LLP | | 2021 |
| Mazaben Enterprises Ltd. | Wholesale & retail | 2014 |
| MB Growth Ltd | Professional & scientific | 2022 |
| MC FOX Ltd | Professional & scientific | 2026 |
| MC Management Services Ltd | Financial services | 2002 |
| MC2 Transition Partners Ltd | Professional & scientific | 2025 |
| MCB UK Services Ltd | Information & communication | 2025 |
| Mckenzie Publishing Limited | Information & communication | 1995 |
| MCW Associates Ltd | Real estate | 1998 |
| MD Constructions(Uk) Ltd | Construction | 2024 |
| Mdola Associate Limited | Construction | 2024 |
| ME2YOU Solutions Ltd | Transport & logistics | 2024 |
| Meal Cottage Ltd | Hospitality | 2014 |
| Medforce (Walton) Limited | Health & social care | 2012 |
| Medical Healthcare Innovations Ltd | Manufacturing | 2020 |
| Medtribe Ltd | Information & communication | 2022 |
| Mega Motor Repairs Ltd | Wholesale & retail | 2022 |
| MEI Fields Designs Limited | Information & communication | 2012 |
| Meja Consulting Ltd | Professional & scientific | 2023 |
| Melissa Handmade Ltd | Wholesale & retail | 2022 |
| Memory Lane Films Limited | Professional & scientific | 2021 |
| Memr Consulting Limited | Professional & scientific | 2023 |
| Mendilec Electrical Maintenance Services Limited | Construction | 2025 |
| Mendilec Limited | Construction | 2016 |
| Menezes Properties | | 2010 |
| Mercury Advisory Services Ltd | Professional & scientific | 2025 |
| Meridian Estates Ventures Ltd | Real estate | 2025 |
| Meridian Machinery Group Ltd | Wholesale & retail | 2026 |
| Meritrule Limited | Transport & logistics | 1986 |
| Merton College London Ltd | Education | 2021 |
| MET Properties EG Ltd | Real estate | 2025 |
| Meta Refurbishments Ltd | Construction | 2019 |
| Metsa Tissue Limited | Wholesale & retail | 1993 |
| MF Business Solutions Ltd | Financial services | 2015 |
| Mgapro Ltd | Health & social care | 2020 |
| Michael Moore (Automobiles) Limited | Professional & scientific | 2025 |
| Michael Ogus Ltd | Professional & scientific | 2023 |
| Migdar Ltd | Professional & scientific | 2023 |
| Mike Dawson Racing Limited | Manufacturing | 2009 |
| Mikey's Carpentry Ltd | Construction | 2020 |
| Milani Services Ltd | Transport & logistics | 2026 |
| Mill Cleave (Byfleet) Limited | Households | 2004 |
| Millwood Hargrave Ltd. | Professional & scientific | 1996 |
| Miloracitiprops Ltd | Professional & scientific | 2023 |
| Mimbridge Limited | Administrative & support | 2008 |
| Mimo Care Services Limited | Health & social care | 2014 |
| Mind's EYE TV Limited | Information & communication | 2011 |
| Minder Solutions Limited | Professional & scientific | 2025 |
| Minds and Millions Ltd | Health & social care | 2025 |
| Mini Hive Ltd | Professional & scientific | 2025 |
| Ministor Limited | Wholesale & retail | 2016 |
| Mint Incorporation Ltd | Professional & scientific | 2024 |
| Mint Source Search Ltd | Administrative & support | 2020 |
| MIO Casa Ltd | Real estate | 2021 |
| Mirar Consulting Services Ltd | Professional & scientific | 2025 |
| Mirmeg Limited | Administrative & support | 2015 |
| Mitchell Communications and PR Ltd | Professional & scientific | 2023 |
| MK Makers London Ltd | Construction | 2023 |
| ML Fire Consultancy Ltd | Public administration | 2020 |
| MLD Consultants Ltd | Professional & scientific | 2014 |
| MLG Invest Limited | Professional & scientific | 2014 |
| MM Handyman Ltd | Construction | 2024 |
| Mmtcg Limited | Wholesale & retail | 2025 |
| Mobile Bikefix LLP | | 2024 |
| Mobiltech INT Ltd | Information & communication | 2011 |
| Modus Nexus Ltd | Wholesale & retail | 2025 |
| Moigne Combe Bloodstock Ltd | Agriculture & fishing | 2021 |
| Moigne Combe Estate Limited | Agriculture & fishing | 2019 |
| Mokome Limited | Professional & scientific | 2012 |
| Mole View Management Company Limited | Professional & scientific | 2011 |
| Monado Partners Limited | Professional & scientific | 2023 |
| Montana Technology Limited | Information & communication | 2014 |
| Montero Logistics Ltd | Transport & logistics | 2026 |
| Moon Milk Ltd | Manufacturing | 2025 |
| Moondrop Cafe Ltd | Hospitality | 2019 |
| Moore by Design Limited | Wholesale & retail | 1980 |
| Moriarty Homes Limited | Real estate | 2021 |
| Motion-Wheelchairs Ltd | Manufacturing | 2025 |
| Motorex Limited | Wholesale & retail | 2024 |
| Motty Media Limited | Information & communication | 2026 |
| Mount ABU (Holdings) Limited | Real estate | 2018 |
| MP Creative Construction Ltd | Construction | 2022 |
| MP Ecommerce Limited | Wholesale & retail | 2024 |