| Lynch Wind Services Limited | Professional & scientific | 2018 |
| Lynn House Ltd | Real estate | 2010 |
| Lyus Plumbing Services Ltd | Construction | 2007 |
| M & I Financial Consultants Ltd | Professional & scientific | 2013 |
| M Benjamin Consulting Limited | Professional & scientific | 2016 |
| M Bourke Build Ltd | Construction | 2018 |
| M Brown TM Ltd | Construction | 2024 |
| M C E a Limited | Real estate | 2019 |
| M Duggan & Sons Limited | Construction | 2010 |
| M G W Building Contractors Limited | Construction | 2018 |
| M J Bushell Audit LLP | | 2014 |
| M J Bushell Holdings Limited | Financial services | 2020 |
| M J Bushell Ltd | Professional & scientific | 2010 |
| M J M Boats Limited | Other services | 2015 |
| M Spicer Consultancy Ltd | Information & communication | 2023 |
| M T O C Ltd | Real estate | 2004 |
| M Wolff Limited | Real estate | 2017 |
| M&A Nour Ltd | Hospitality | 2024 |
| M&M Grosu Ltd | Construction | 2023 |
| M&P Info Ltd | Information & communication | 2010 |
| M&S Construction Solutions Ltd | Construction | 2025 |
| M&S Fuel Services Ltd | Wholesale & retail | 2015 |
| M&S On-Time Services Ltd | Professional & scientific | 2014 |
| M&S Ontime Property Ltd | Real estate | 2023 |
| M&S Trading Express Ltd | Wholesale & retail | 2024 |
| M-Best Consultants Limited | Construction | 2023 |
| M. P. Prime Mechanical Limited | Construction | 2024 |
| M.C.C. Shenfield Ltd | Real estate | 2025 |
| M.D.M. Medical Limited | Wholesale & retail | 1991 |
| M.J. Performance Limited | Arts & recreation | 2000 |
| M.Ling Electrical Ltd | Construction | 2023 |
| M.T. Technical Services Limited | Construction | 2000 |
| M4SIZ Limited | Information & communication | 2007 |
| M5 Homes Ltd | Real estate | 2024 |
| M7 Ventilation Ltd | Energy | 2024 |
| MA Structures Limited | Manufacturing | 2025 |
| MAC Macs Live Stream Ltd | Information & communication | 2018 |
| Macca Financial Services Limited | Professional & scientific | 2022 |
| Machu Group Ltd | Professional & scientific | 2025 |
| Macsade Roofing Ltd | Construction | 2020 |
| Maddor Ltd | Professional & scientific | 2018 |
| Madds Properties LLP | | 2021 |
| Made in Heaven (Essex) Ltd | Manufacturing | 2022 |
| Madi Interior Solutions Ltd | Construction | 2021 |
| Madigangill&Cleaning Limited | Construction | 2019 |
| Madison Reign Ltd | Administrative & support | 2018 |
| Madrugada Hospitality Limited | Hospitality | 2022 |
| Magdalena Wrzeszcz Ltd | Professional & scientific | 2021 |
| Magee Mechanical & Electrical Limited | Construction | 2026 |
| Magenta CAPITAL2 Ltd | Professional & scientific | 2009 |
| Magic Bound UK Ltd | Wholesale & retail | 2022 |
| Magma Diamonds International Limited | Manufacturing | 2019 |
| Magnifica Construction Ltd | Construction | 2019 |
| Magnur Capital Ltd | Financial services | 2024 |
| Magpie Solutions Ltd | Transport & logistics | 2006 |
| Magpies Nest Homes Ltd | Real estate | 2025 |
| Maid Cleanly Ltd | Administrative & support | 2024 |
| Mainlake Properties Ltd | Real estate | 2021 |
| Mainspring Web Television Company Ltd | Information & communication | 2010 |
| Maintain Group Ltd | Construction | 2022 |
| Maison D'If Limited | Wholesale & retail | 2019 |
| Maison Lodge Properties Ltd | Construction | 2024 |
| Maison Quill Ltd | Information & communication | 2025 |
| Maitland and Kensington Associates Ltd | Administrative & support | 2016 |
| Majage Limited | Information & communication | 2014 |
| Majenta House Limited | Construction | 2016 |
| Make UP Style Limited | Wholesale & retail | 2010 |
| MAL Fire and Electrical Services Limited | Construction | 2025 |
| Malbridge Finance Limited | Financial services | 1973 |
| Maldon Dental Care Ltd | Health & social care | 2025 |
| Maldon Direct Limited | Wholesale & retail | 2010 |
| Malik Logistics Ltd | Administrative & support | 2020 |
| Mallard Electrical LLP | | 2021 |
| Malula CIC | Manufacturing | 2026 |
| Mama's Best Group Ltd | Wholesale & retail | 2024 |
| Mamaandminis Limited | Professional & scientific | 2024 |
| Mammaz Foods Limited | Hospitality | 2016 |
| Mamsbiege Ltd | Health & social care | 2015 |
| Management Systems International Limited | Extraterritorial | 1992 |
| Mandeville Place (Radwinter) Management Limited | Households | 2016 |
| Mane Edition Limited | Manufacturing | 2025 |
| Manforce Facilities Management Ltd | Administrative & support | 2022 |
| Manford Way FC Catering Ltd | Hospitality | 2022 |
| Mangia Bene Limited | Hospitality | 2014 |
| Manifolds Care Ltd | Administrative & support | 2025 |
| Manifolds Group Ltd | Administrative & support | 2020 |
| Manley & Co Holdings Ltd | Real estate | 2026 |
| Manly Environmental Services Limited | Professional & scientific | 2010 |
| Mann Island Estate Limited | Households | 2014 |
| Mannat Homes Limited | Real estate | 2025 |
| Mannings Group UK Ltd | Arts & recreation | 2016 |
| Mannix Maintenance Limited | Water & waste | 2014 |
| Mano & Nirupa Ltd | Administrative & support | 2018 |
| Manor 33 Limited | Construction | 2018 |
| Manor Beauty Limited | Other services | 2015 |
| Manor Court Management (Benfleet) Ltd | Households | 2016 |
| Manor Grange Property Management Limited | Households | 2022 |
| Manor Place Hotel Ltd | Hospitality | 2014 |
| Mansell Street Garage Limited | Wholesale & retail | 1955 |
| Mapa Group Limited | Construction | 2017 |