| Mamu 21 Ltd | Wholesale & retail | 2025 |
| Mana Services Limited | Construction | 2016 |
| Mangal Grill Ltd | Hospitality | 2025 |
| Manor Tree Services Ltd | Administrative & support | 2021 |
| Manto Investment Ltd | Real estate | 2026 |
| MAR Services Limited | Households | 2025 |
| Marc James Limited | Wholesale & retail | 2025 |
| Mardel Roofing Contractors Ltd | Construction | 2003 |
| Margie Studio Limited | Professional & scientific | 2020 |
| Margreat Ltd | Hospitality | 2020 |
| Maria Markham Estates Ltd | Real estate | 2026 |
| Mark Aurelius Ltd | Wholesale & retail | 2022 |
| Mark Dimmock Limited | Administrative & support | 2016 |
| Market Kebab House Limited | Hospitality | 1999 |
| Markku Constrcutions Ltd | Construction | 2025 |
| Marleigh Estate Management Company Limited | Real estate | 2020 |
| Marleigh Phase 1 Limited | Construction | 2020 |
| Mars Consultation Limited | Wholesale & retail | 2025 |
| Marsengo's Ltd | Hospitality | 2023 |
| Marshall Decorating & Property Services Ltd | Construction | 2023 |
| Martin Dannell and Company Limited | Wholesale & retail | 1982 |
| Martorana Property Limited | Real estate | 2016 |
| Masari Ltd | Administrative & support | 2016 |
| Mase One Limited | Professional & scientific | 2013 |
| Mash and Dash Limited | Hospitality | 2025 |
| Mason Carminati Ltd | Administrative & support | 2023 |
| Master Fit Pack Limited | Other services | 2025 |
| Mauri & Souza Properties Ltd | Real estate | 2020 |
| Mauu Services Ltd | Construction | 2025 |
| MAY Design & Construction Ltd | Construction | 2017 |
| May-Wick Entertainment Limited | Information & communication | 2015 |
| Maya Bakery Ltd | Hospitality | 2024 |
| Maya Privé Limited | Hospitality | 2026 |
| Mazi Barber Ltd | Other services | 2026 |
| MB Magic Repairs Ltd | Construction | 2016 |
| MB Rope Access Ltd | Construction | 2024 |
| MB91 Ltd | Transport & logistics | 2019 |
| Mbsa Construction Ltd | Real estate | 2021 |
| MC Property Stays Ltd | Hospitality | 2024 |
| Mccarthy Steel Ltd | Construction | 2017 |
| Mccfit Labs Ltd | Other services | 2023 |
| Mccs Group Ltd | Real estate | 2020 |
| Mckay Ball Associates Ltd | Professional & scientific | 2019 |
| Mckinsey Memorial Business Consultancy Limited | Professional & scientific | 2025 |
| MCP Shipping Limited | Wholesale & retail | 2012 |
| MD Euphoria Ltd | Hospitality | 2021 |
| MD HQ Ltd | Agriculture & fishing | 2025 |
| MD Sevov Limited | Transport & logistics | 2011 |
| MD Stiles Roofing Ltd | Construction | 2023 |
| Mdere Limited | Hospitality | 2025 |
| Mdha Limited | Information & communication | 2017 |
| Mdjj Property Limited | Real estate | 2023 |
| Mdminou Limited | Health & social care | 2016 |
| Mead Property Investments Ltd | Real estate | 2025 |
| Meadperry Management Company Limited(The) | Households | 1986 |
| MED5 Ltd | Hospitality | 2025 |
| Medi Food Centre Limited | Manufacturing | 2023 |
| Medico Staffing Limited | Health & social care | 2015 |
| Mediplacements Limited | Health & social care | 2011 |
| Medsen Centre Ltd | Education | 2021 |
| Medz UK Limited | Wholesale & retail | 2017 |
| Meet Finance Ltd | Professional & scientific | 2021 |
| Mega Kebab House Ltd | Hospitality | 2024 |
| Mega Sign Star Ltd | Professional & scientific | 2025 |
| Megawatt Electrical Ltd | Construction | 2025 |
| Meit Associates Ltd | Construction | 2024 |
| MEK Properties Limited | Real estate | 2004 |
| MEL Healthcare Limited | Health & social care | 2020 |
| Meleklerim Ltd | Real estate | 2024 |
| Mellow Brasserie Ltd | Hospitality | 2026 |
| Memhas Holdings Limited | Financial services | 2019 |
| Memo the Barber Ltd | Other services | 2025 |
| Memoize Parfum Ltd | Manufacturing | 2018 |
| Memz Entertainment Limited | Hospitality | 2025 |
| MER Foods Ltd | Manufacturing | 2020 |
| Mercy Denied Ltd | Other services | 2024 |
| Meridian Hill (Chigwell) Limited | Construction | 2012 |
| Merronwain Limited | Other services | 2012 |
| Mert OZ Limited | Hospitality | 2018 |
| Mesa Bistro Limited | Hospitality | 2026 |
| Mesopotamia Pizza & Kebab Ltd | Hospitality | 2023 |
| Messy Master Ltd | Other services | 2023 |
| Metin UK Visa Solutions Limited | Professional & scientific | 2020 |
| MF Accountants & Bookkeepers Ltd | Professional & scientific | 2018 |
| MF11TAX Ltd | Extraterritorial | 2023 |
| MFL Roofing & Maintenance Limited | Construction | 2025 |
| MG Heating Limited | Construction | 2009 |
| MG Interior Refurbishments Limited | Construction | 2014 |
| Mgamanagement Ltd | Real estate | 2022 |
| MGM Clinics Ltd | Health & social care | 2016 |
| MGN Drywall Ltd | Construction | 2020 |
| MH8 Management Limited | Households | 2024 |
| MIB Motors Ltd | Wholesale & retail | 2025 |
| Micar Computer Systems Limited | Information & communication | 1989 |
| Microtech 03 Limited | Information & communication | 2003 |
| Middle Watch (Swavesey) Residents Management Company Limited | Households | 2026 |
| Miha Design & Build Ltd | Construction | 2022 |
| Mika Carpentery&Joinery Ltd | Manufacturing | 2025 |
| Miles Property Developments (MPD) Ltd | Real estate | 2020 |
| Million to Billion Ltd | Professional & scientific | 2022 |