| Mannok Insulation (GB) Limited | Wholesale & retail | 2006 |
| Mannok Pack (GB) Limited | Administrative & support | 2020 |
| Manor Farm (Cliffe) Management Company Limited | Households | 2019 |
| Mansio Divina Ltd | Construction | 2023 |
| Mantle Underfloor Heating Ltd | Manufacturing | 2025 |
| Manus Legal Affairs Ltd | Professional & scientific | 2012 |
| Marabel Gardens Management Limited | Households | 2021 |
| Marblematch Limited | Administrative & support | 1996 |
| Marc Lawes Sound Limited | Information & communication | 2022 |
| March Branding Ltd | Professional & scientific | 2015 |
| March Developments Ltd. | Hospitality | 1993 |
| Marches Construction Management Ltd | Professional & scientific | 2016 |
| Marcus INT Concept Ltd | Administrative & support | 2017 |
| Marden Maintenance Limited | Construction | 2016 |
| Marian Trans Limited | Transport & logistics | 2014 |
| Marianna Obafemi Interiors Ltd | Professional & scientific | 2020 |
| Marie Neave Limited | Education | 2025 |
| Marine & Country Limited | Wholesale & retail | 2025 |
| Marine and Civil Diving Services Ltd | Construction | 2020 |
| Marinov Transport Ltd | Transport & logistics | 2023 |
| Marion Bay Holdings Ltd | Households | 2022 |
| Mark Anthony Cummings Ltd | Wholesale & retail | 2015 |
| Market Building Events Ltd | Hospitality | 2025 |
| Markmedics-Consult Limited | Health & social care | 2020 |
| Marlin Studio Limited | Manufacturing | 2022 |
| Marlow Find Ltd | Transport & logistics | 2012 |
| Marmet Construction Ltd | Construction | 2024 |
| Marquis Installations Ltd | Construction | 2010 |
| Marriageatcana | Other services | 2018 |
| Marriott Residences Limited | Real estate | 2015 |
| Marseille Housing Project Limited | Real estate | 2001 |
| Martin Engineering Services Limited | Construction | 2022 |
| Martin Environmental Services Limited | Construction | 1998 |
| Martin Insurance Services Ltd | Financial services | 1996 |
| Martinair Compressors Limited | Manufacturing | 2003 |
| Martinfamilymemorialcare Ltd | Other services | 2026 |
| Martini Investments Ltd | Real estate | 2013 |
| Marvel Ovens & Laundry Ltd | Other services | 2025 |
| Marydave Associates Limited | Real estate | 2018 |
| MAS Exports Limited | Wholesale & retail | 2025 |
| Masefield Productions Ltd | Administrative & support | 2023 |
| Mason's Financial Services Ltd | Financial services | 2026 |
| Mass Business Consultancy Ltd | Professional & scientific | 2020 |
| Mastacab (South East) Limited | Manufacturing | 2016 |
| Mastacab Kent LLP | | 2016 |
| Master Builders Kent Ltd | Construction | 2026 |
| Master Painting and Decorating Ltd | Construction | 2019 |
| Masterclass Insight Limited | Professional & scientific | 2005 |
| Masters Kebab Ltd | Hospitality | 2017 |
| Mataz Services Ltd | Extraterritorial | 2023 |
| Matchmarble Limited | Administrative & support | 2024 |
| Matchstick Trees Limited | Health & social care | 2025 |
| Matrix Labs Ltd | Financial services | 2017 |
| Matsam CAD Services Limited | Information & communication | 1997 |
| Matter Solutions Kent Ltd | Manufacturing | 2026 |
| Matty Hurst Productions Ltd | Arts & recreation | 2024 |
| Mavatie Oxywellness Limited | Health & social care | 2025 |
| Maven Strategic Ltd | Education | 2020 |
| Maverick Ladies Lounge Limited | Hospitality | 2023 |
| Maverick RR Holdings Limited | Financial services | 2023 |
| Maverick-Group Limited | Real estate | 2022 |
| Maverickner Ltd | Arts & recreation | 2024 |
| Maxbrands Marketing Ltd | Manufacturing | 2021 |
| Maydanoz Ltd | Hospitality | 2016 |
| Mayflower Heights Residents Association Limited | Households | 2003 |
| Mayfourth Properties Ltd | Real estate | 2020 |
| Mayhow Ltd | Construction | 2024 |
| Mays Lions Scaffolding Ltd | Construction | 2019 |
| Mayverita Limited | Professional & scientific | 2026 |
| Maziko Ltd | Real estate | 2019 |
| MB Asbestos Surveys Ltd | Administrative & support | 2020 |
| MB Strategic Holdings Limited | Financial services | 2024 |
| Mbdistributioner Ltd | Wholesale & retail | 2026 |
| MBM Readymix Ltd | Manufacturing | 2023 |
| Mc/Cro Partnership Ltd | Hospitality | 2024 |
| MC7 Marketing Ltd | Other services | 2023 |
| Mccoys Frinsbury Limited | Hospitality | 2018 |
| Mccullochs (CI3) Limited | Construction | 2020 |
| Mccullochs [CI] Limited | Real estate | 2002 |
| MCE Windows Ltd | Manufacturing | 2025 |
| Mcevans K Limited | Health & social care | 2015 |
| Mckenna Utilities Ltd | Construction | 2021 |
| Mclands Estates Ltd | Real estate | 2021 |
| Mcneil Homecare Limited | Health & social care | 2013 |
| Mcnichol Scaffolding Solutions Ltd | Construction | 2019 |
| Mcr-Uk Ltd | Wholesale & retail | 2010 |
| MCS Chicken World Limited | Hospitality | 2025 |
| MCS Medway (Holdings) Limited | Financial services | 2017 |
| MCS Skip Hire Ltd | Water & waste | 2026 |
| Mcvaliant Consulting Ltd | Information & communication | 2026 |
| Mddr Investments Ltd | Administrative & support | 2023 |
| MDF Consult Limited | Construction | 2025 |
| MDT House Limited | Other services | 2020 |
| Me.You.Us.Together Ltd | Administrative & support | 2024 |
| ME1 Build Ltd | Construction | 2023 |
| ME1 Mechanical and Electrical Limited | Construction | 2017 |
| Meadowridge Limited | Administrative & support | 2000 |
| Meadowview (IOG) Freehold Management Ltd | Households | 2013 |
| Measure Once CUT Twice Ltd | Manufacturing | 2021 |
| MEC Global Services Limited | Transport & logistics | 2025 |