| Lyn's Best Sellers Ltd | Manufacturing | 2020 |
| Lynx Eco Limited | Construction | 2024 |
| M & D Trash Masters Limited | Water & waste | 2026 |
| M & T Real Estate Ltd | Real estate | 2026 |
| M & W Services Ltd | Administrative & support | 2008 |
| M D Processing Limited | Construction | 2023 |
| M Engine Services Ltd | Wholesale & retail | 2024 |
| M Hall Communications Ltd | Information & communication | 2025 |
| M Project Engineering Ltd | Wholesale & retail | 2023 |
| M R Healthcare Services Ltd | Administrative & support | 2024 |
| M&A 1905 Ltd | Hospitality | 2025 |
| M&M Acorn Ltd | Construction | 2020 |
| M&M Fitness Studio Ltd | Arts & recreation | 2021 |
| M&M Legal Service Ltd | Professional & scientific | 2024 |
| M. Hoole Holdings Ltd | Financial services | 2023 |
| M.Hoole Contracting Ltd | Administrative & support | 2019 |
| M.J Aesthetics Ltd | Other services | 2025 |
| M.K.P Electrical Solutions Limited | Construction | 2025 |
| M.Stali Ltd | Construction | 2023 |
| M2 Tyres Ltd | Wholesale & retail | 2023 |
| M3OWEN Ltd | Other services | 2011 |
| MA BMS Electrical Ltd | Agriculture & fishing | 2017 |
| MA Ecom & Global Trading Ltd | Wholesale & retail | 2026 |
| MAC Consultancy Ltd | Professional & scientific | 2022 |
| Macec Limited | Construction | 2014 |
| Macflorenz Limited | Health & social care | 2020 |
| Mack's Property Group Limited | Real estate | 2026 |
| MAD Constructor Ltd | Construction | 2023 |
| MAD Electrics Limited | Construction | 2015 |
| MAD Utility Ltd | Construction | 2023 |
| Maddan Construct Services Limited | Construction | 2024 |
| Maddel Ltd | Administrative & support | 2024 |
| Madina Halal Food Limited | Hospitality | 2024 |
| Magben Ltd | Real estate | 2014 |
| Magellan Surveys Limited | Professional & scientific | 2021 |
| Magic MEN London Ltd | Construction | 2012 |
| Magic PAM Ltd | Wholesale & retail | 2017 |
| Magnet Sentinel Limited | Construction | 2014 |
| Mahirlondon.Com Ltd | Wholesale & retail | 2010 |
| Mahmood & Humaira Ltd | Information & communication | 2025 |
| Mahn Group Holdings Ltd | Financial services | 2025 |
| Maijar Ltd | Real estate | 2019 |
| Maisan Goods PVT Ltd | Wholesale & retail | 2025 |
| Maison Pure Ltd | Administrative & support | 2025 |
| Majeja Ventures Limited | Health & social care | 2009 |
| Makazey-Essence of Life Ltd | Health & social care | 2017 |
| Malox Entertainment Ltd | Information & communication | 2026 |
| Malusardi Williams Ltd | Wholesale & retail | 2025 |
| Mama on Duty Ltd | Administrative & support | 2017 |
| Mamadupsy Ltd | Real estate | 2013 |
| Mandy Nyahunda Limited | Health & social care | 2022 |
| Manor Container Line Limited | Transport & logistics | 1993 |
| Manor Shipping Services Limited | Transport & logistics | 1985 |
| Manor Western Air Limited | Transport & logistics | 1993 |
| Maqcorp UK Ltd | Information & communication | 2024 |
| Marcaspus Ltd | Administrative & support | 2024 |
| Mardyke Miniature Railways Limited | Arts & recreation | 1981 |
| Mardyke Youth and Community Association | Other services | 2002 |
| Marenza Ltd | Wholesale & retail | 2025 |
| Margheritas Deal Ltd | Hospitality | 2025 |
| Marhale Limited | Construction | 2017 |
| Marian B Transport Limited | Transport & logistics | 2025 |
| Marian Popa Ltd | Construction | 2015 |
| Marian Razvan Ltd | Transport & logistics | 2021 |
| Maris Groundwork Ltd | Construction | 2021 |
| Markben Construction Ltd | Construction | 2018 |
| Marketmile Ltd | Wholesale & retail | 2026 |
| Marlow Services Ltd | Water & waste | 2017 |
| Mars Building Contractors Ltd | Construction | 2018 |
| Marsand Bespoke Furniture Limited | Other services | 2018 |
| Martton Limited | Construction | 2007 |
| Marvel Healthcare Limited | Health & social care | 2013 |
| Marydania Limited | Health & social care | 2023 |
| Mason Interim Services Ltd | Professional & scientific | 2009 |
| Mason Pearson Bros. Limited | Manufacturing | 1973 |
| Mason Pearson Brothers Limited | Extraterritorial | 2001 |
| Mason Pearson Limited | Extraterritorial | 2001 |
| Masquerade London Limited | Administrative & support | 2019 |
| MAT Code Limited | Manufacturing | 2019 |
| Matei Haulage Ltd | Transport & logistics | 2018 |
| Mateiproperties. Ltd | Real estate | 2022 |
| Matrix Bay Ltd | Wholesale & retail | 2025 |
| Matthew Collins Limited | Administrative & support | 2012 |
| MAX Target Property Ltd | Real estate | 2026 |
| Maxsec UK Limited | Administrative & support | 2024 |
| Maxxicare Ltd | Administrative & support | 2020 |
| MAY Glass Recycling Limited | Water & waste | 2013 |
| May&Mike Cliveland Ltd | Real estate | 2022 |
| Maya Candy Bar Ltd | Wholesale & retail | 2022 |
| Mayfield Grove Residents Association Limited | Households | 2009 |
| Mayra Chohan Ltd | Wholesale & retail | 2025 |
| Mazu London Ltd | Wholesale & retail | 2023 |
| MB Eagle Shipping Ltd | Transport & logistics | 2023 |
| MB Estate Development Ltd | Real estate | 2023 |
| MB Lets Limited | Real estate | 2020 |
| Mbello Ltd | Health & social care | 2018 |
| MBO Construction Ltd | Construction | 2015 |
| MC Rendering Ltd | Construction | 2023 |
| MC Sealants Ltd | Construction | 2021 |
| MCA Care Resourcing Limited | Health & social care | 2025 |