| MSC (Kent) Limited | Wholesale & retail | 2002 |
| MSC Business Advisory Services Limited | Administrative & support | 2020 |
| Msgglobaltrading Ltd | Wholesale & retail | 2022 |
| Msha Properties Ltd | Real estate | 2025 |
| MSI Enterprises Ltd | Wholesale & retail | 2023 |
| MSI Ltd | Financial services | 2016 |
| Msi-Aci UK Limited | Professional & scientific | 2022 |
| Msiba Ltd | Professional & scientific | 2023 |
| MSJ Newsagents Ltd | Wholesale & retail | 2002 |
| MSK Music UK Limited | Information & communication | 2014 |
| Mspalani Ltd | Wholesale & retail | 2026 |
| MSR Concepts Ltd | Information & communication | 2014 |
| MSR Evolution Limited | Professional & scientific | 2024 |
| MSV Digital Ltd | Information & communication | 2020 |
| MT Autoctr Window Tinting Ltd | Wholesale & retail | 2025 |
| MT Defence Limited | Professional & scientific | 2014 |
| MT House Limited | Real estate | 2020 |
| Mtad Holdings Ltd | Information & communication | 2023 |
| MTD Sheets Ltd | Information & communication | 2023 |
| Mtek Civil Engineering Ltd | Construction | 2020 |
| MTF Funding Limited | Professional & scientific | 2013 |
| Mtglow Limited | Health & social care | 2026 |
| Mthorne Ltd | Arts & recreation | 2025 |
| MTP Accountancy Services Limited | Professional & scientific | 2011 |
| MTS Services Ltd | Professional & scientific | 2023 |
| Much Cleaner Ltd | Administrative & support | 2026 |
| Mudpark Investment Limited | Professional & scientific | 2023 |
| Mujo Motor Ltd | Other services | 2019 |
| Mula Cake Kids Club Community Interest Company | Education | 2014 |
| Mula Cake Limited | Wholesale & retail | 2012 |
| MULAN256 Ltd | Transport & logistics | 2025 |
| Mularjuice Limited | Wholesale & retail | 2024 |
| Mulberry Court (Croydon) Management Limited | Households | 1997 |
| Mulberry Court 28-31 RTM Company Limited | Households | 2010 |
| Mulberry Gardens Residents Management Company Limited | Households | 2013 |
| Mulberry Heights Residents Company Limited | Households | 2015 |
| Mulberry International Ltd | Wholesale & retail | 2000 |
| Mulberry Mews Residents Management Company Limited | Households | 2006 |
| Mulberry Park Apartments (Management Company) Limited | Households | 2019 |
| Mulberry Place (Farnham) Management Company Limited | Households | 2013 |
| Mulhall Enterprises Ltd | Professional & scientific | 2014 |
| Mulier Coffee Ltd | Wholesale & retail | 2023 |
| Multi Maintenance Solutions Limited | Professional & scientific | 2007 |
| Multi-Electronics Limited | Manufacturing | 2017 |
| Multigap Residents Management Limited | Households | 1987 |
| Multikey Security Services Limited | Administrative & support | 2002 |
| Multinvestment Limited | Real estate | 2023 |
| Multiple.Invest Ltd | Wholesale & retail | 2016 |
| Multiplug Management Limited | Professional & scientific | 2016 |
| Mummy African Caribbean Food Ltd | Hospitality | 2018 |
| Mummy's Services Ltd | Administrative & support | 2023 |
| Mumtrepreneur Services Ltd | Administrative & support | 2018 |
| Munchies Cafe (Mottingham) Limited | Hospitality | 2015 |
| Mundowab Ltd | Manufacturing | 2025 |
| Mungo Park Pharma Ltd | Wholesale & retail | 2026 |
| Muphovi Ltd | Information & communication | 2014 |
| Mura App Ltd | Transport & logistics | 2020 |
| Murabet Ltd | Construction | 2025 |
| Muradpur Properties Limited | Real estate | 2020 |
| Murgitroyd (Creation IP Europe) Limited | Professional & scientific | 2013 |
| Murgitroyd (Tlip) Limited | Professional & scientific | 2014 |
| Murphy Consulting Ltd | Professional & scientific | 2013 |
| Murraycs Homes Ltd | Extraterritorial | 2023 |
| MUS Electrical Ltd | Construction | 2022 |
| MUS Props Ltd | Real estate | 2016 |
| Musa & Brothers Limited | Real estate | 2025 |
| Musa Creative Limited | Wholesale & retail | 2019 |
| Musaayah Essence Ltd | Wholesale & retail | 2025 |
| Musamir Ltd | Hospitality | 2024 |
| Musarrat Homes and Housing Ltd | Financial services | 2024 |
| Museum of Diversity Ltd | Education | 2021 |
| Music Festivals at Sea Limited | Arts & recreation | 2000 |
| Music NXT GEN Academy Community Interest Company | Education | 2024 |
| Music Room App Ltd | Other services | 2023 |
| Musical Movements Limited | Other services | 2013 |
| Musicalisters Ltd. | Education | 2014 |
| Muson Trade Limited | Wholesale & retail | 2024 |
| Mussenden Court Management Limited | Households | 1989 |
| Mustard Seed Procurement UK Ltd | Administrative & support | 2016 |
| Mustgetacard.Com Limited | Wholesale & retail | 2010 |
| Musti's Pound Plus Ltd | Wholesale & retail | 2009 |
| Muta MA TOO Ltd | Other services | 2023 |
| Mutebuka & Co Immigration Lawyers Ltd | Professional & scientific | 2010 |
| Mutual Capital Limited | Real estate | 2020 |
| Muupi Ltd | Information & communication | 2024 |
| MV Construction Shine Ltd | Construction | 2024 |
| MVI Trade Ltd | Construction | 2016 |
| Mvir Services Ltd | Transport & logistics | 2021 |
| MW Air Conditioning Services Limited | Energy | 2019 |
| MW Partnership Limited | Information & communication | 2020 |
| MW Plumbing & Heating Services Limited | Construction | 2018 |
| Mwasami Limited | Information & communication | 2011 |
| Mwill Ltd | Information & communication | 2025 |
| Mwjt Consulting Ltd | Health & social care | 2024 |
| MWQ Limited | Other services | 2010 |
| MWS Plumbing Services Ltd | Construction | 2026 |
| My Banner CIC | Other services | 2024 |
| My Black CAB Limited | Transport & logistics | 2016 |
| My Designer Properties Limited | Households | 2020 |
| My Desk Space Ltd | Real estate | 2023 |