| Megap Group Ltd | Wholesale & retail | 2019 |
| Mehmi Property Investments Limited | Real estate | 2006 |
| Meis Management Consultancy Ltd | Administrative & support | 2025 |
| Meis Solutions Ltd | Administrative & support | 2025 |
| Mekhprop Limited | Real estate | 2026 |
| Melbrook Property Management Limited | Real estate | 1983 |
| Meli Art Ltd | Manufacturing | 2023 |
| Melon Investments Limited | Financial services | 2023 |
| Memory Index Ltd | Information & communication | 2025 |
| Memory Lane Publishing Ltd | Information & communication | 2023 |
| Mensch Music Management Ltd | Information & communication | 2026 |
| Mentes Serena Ltd | Health & social care | 2019 |
| Menvo Limited | Real estate | 2004 |
| MEP Industry Limited | Wholesale & retail | 2013 |
| Mera Electrical Services Ltd | Construction | 2024 |
| Merchant & Associates Limited | Construction | 2018 |
| Mercidez Ltd | Real estate | 2020 |
| Mercurius Medical Services Limited | Health & social care | 2007 |
| Mercym Limited | Manufacturing | 2013 |
| Meridian Care Solutions Ltd | Health & social care | 2026 |
| Merit Building Company Limited | Construction | 1983 |
| Merlietroysebastian Limited | Professional & scientific | 2011 |
| Merlin Environmental Holdings Limited | Financial services | 2026 |
| Merlin Environmental Solutions Limited | Professional & scientific | 2011 |
| Merlin Plastering Limited | Construction | 1985 |
| Merlin Truline Roofing Limited | Construction | 2004 |
| Merlyn Mind UK Limited | Education | 2021 |
| Merryacres Limited | Professional & scientific | 2013 |
| Merve Properties Ltd | Real estate | 2026 |
| Mesfer Brothers Limited | Administrative & support | 2014 |
| Mesh Accommodation Ltd | Real estate | 2022 |
| Mesh Stays Ltd | Administrative & support | 2025 |
| Mesi Estates Ltd | Real estate | 2021 |
| Meson Tax Ltd | Information & communication | 2022 |
| Metabyt UK Ltd | Information & communication | 2022 |
| Metacollective Limited | Information & communication | 2021 |
| Metalart Fabrication Ltd | Manufacturing | 2008 |
| Metalbor Limited | Manufacturing | 1946 |
| Metallic Autos Limited | Wholesale & retail | 2013 |
| Metalwork by Design Ltd | Manufacturing | 2018 |
| METGAS1 Ltd | Construction | 2022 |
| Metier International Ltd | Administrative & support | 2022 |
| Metro Enforcement Ltd | Administrative & support | 2016 |
| Metz Construction Ltd | Construction | 2005 |
| Mexemco Ltd | Wholesale & retail | 2021 |
| Mextrade Ltd | Wholesale & retail | 2009 |
| Meze & Shish Ltd | Hospitality | 2016 |
| MF Endo Ltd | Health & social care | 2024 |
| MF Waste Limited | Water & waste | 2024 |
| Mfdisvovery Limited | Professional & scientific | 2019 |
| MG Financial Services ( PVT) Ltd | Financial services | 2020 |
| MGB Electrical (U.K.) | | 1996 |
| MGE Consulting Ltd | Information & communication | 2019 |
| MGM Plumbing Supplies Ltd | Wholesale & retail | 2022 |
| MGS Investments Ltd | Real estate | 2018 |
| MGT Construction Limited | Construction | 2007 |
| MH Roofing Services Ltd | Construction | 2025 |
| MH Surveyor Ltd | Administrative & support | 2020 |
| MHC Technologies Limited | Information & communication | 2007 |
| Mhene Healthcare Limited | Health & social care | 2015 |
| Mian Developers Limited | Real estate | 2026 |
| MIB Tech Consulting Ltd | Professional & scientific | 2015 |
| Michael and Henrietta Spink Limited | Wholesale & retail | 1988 |
| Michael Education Centre Ltd | Education | 2009 |
| Michael K Accounting Services Ltd | Professional & scientific | 2017 |
| Michele Yeomans Ltd | Professional & scientific | 2010 |
| Micro - Signature Limited | Professional & scientific | 2014 |
| Mictec Ltd | Administrative & support | 2011 |
| Midas Portal Limited | Financial services | 2017 |
| Midas Property Portal Ltd | Real estate | 2017 |
| Midlax Property Management Ltd | Real estate | 2022 |
| Miell Electrical (London) Ltd | Construction | 2018 |
| Mighty Minis Racing Ltd | Arts & recreation | 2003 |
| Miha Care Limited | Health & social care | 2023 |
| Mika London Limited | Real estate | 2010 |
| Mike Carr Services Limited | Wholesale & retail | 2017 |
| Mikeronet Ltd | Information & communication | 2016 |
| Miku Studios Ltd | Manufacturing | 2026 |
| Mila Maeva Ltd | Wholesale & retail | 2021 |
| Mili Lifestyle Limited | Hospitality | 2020 |
| Milkman of Human Kindness Limited | Arts & recreation | 2019 |
| Millen & Associates Ltd | Administrative & support | 2025 |
| Millen Compliance Limited | Administrative & support | 2012 |
| Millennium EVC Ltd | Construction | 2022 |
| Millennium House Sussex Limited | Real estate | 2010 |
| Miller & Roberts Property Holdings Ltd | Financial services | 2015 |
| Milletrade Ltd | Construction | 1999 |
| Millside Residents Association Limited | Households | 1992 |
| Millstone Dynamics Ltd | Manufacturing | 2026 |
| Milly Consulting Limited | Administrative & support | 2022 |
| Milsom Builders Limited | Construction | 1999 |
| Milvian Group UK & Europe Limited | Information & communication | 2025 |
| Milward Property Developments Ltd | Construction | 2018 |
| Mimi E Coco Ltd | Hospitality | 2003 |
| Minaeva Surveys Limited | Professional & scientific | 2016 |
| Minetoybox Ltd | Wholesale & retail | 2025 |
| Ming TAK Chinese School | Education | 1995 |
| Mint Heating & Plumbing Limited | Construction | 2026 |
| Mint Marquees Ltd | Administrative & support | 2023 |
| Miomni Gaming Limited | Information & communication | 2011 |