| Marina Mini Market Ltd | Wholesale & retail | 2024 |
| Marine Advisory Experts Limited | Professional & scientific | 2023 |
| Mariner Facilities Management Limited | Administrative & support | 2008 |
| Mark & Neil Property Limited | Real estate | 2022 |
| Mark Haynes Limited | Transport & logistics | 2016 |
| Mark Heath Consulting Ltd | Administrative & support | 2015 |
| Mark Paul Strutt Developments Limited | Construction | 2017 |
| Marke Consultancy Ltd | Professional & scientific | 2019 |
| Markhor Ventures Ltd | Professional & scientific | 2019 |
| Marlborough Bakery (Chislehurst) Ltd | Wholesale & retail | 2020 |
| Marlow Grey Limited | Professional & scientific | 2026 |
| Marmic Developments Ltd | Construction | 2025 |
| Marney Roofing Ltd | Construction | 2026 |
| Maroko Limited | Real estate | 2020 |
| Marple Elevators Limited | Construction | 2005 |
| Mars Hill Cosmetics Limited | Wholesale & retail | 2013 |
| Marsh and Fallow Ltd | Agriculture & fishing | 2024 |
| Marshall E Paving Ltd | Construction | 2024 |
| Marshalls Electrical Limited | Administrative & support | 2005 |
| Martin Carr Estates Ltd | Real estate | 2010 |
| Martin Ives & Company Limited | Administrative & support | 2010 |
| Martin Properties South East Ltd | Real estate | 2023 |
| Martir Properties Limited | Real estate | 2025 |
| Martsons Recycling Group Ltd | Construction | 2023 |
| Marvelarc Projects Ltd | Information & communication | 2014 |
| Marvellous MEN Ltd | Construction | 2023 |
| Mascot Event Limited | Hospitality | 2022 |
| Mase Global Services Limited | Wholesale & retail | 2018 |
| Mashallah Limited | Hospitality | 2026 |
| Mason Alexander Property Investments Ltd | Real estate | 2026 |
| Mason Estates Ltd | Real estate | 2017 |
| Mass Holdings and Investments Limited | Professional & scientific | 2017 |
| Mast Scaffolding Ltd | Construction | 2018 |
| Master Skip Ltd | Water & waste | 2001 |
| Mastercraft Maintenance (Kent) Ltd | Real estate | 2023 |
| Matachi Ltd | Other services | 2020 |
| Matella Burger II Limited | Administrative & support | 2012 |
| Mathew John Limited | Information & communication | 2014 |
| Mathew K Sutton Funeral Services Ltd | Other services | 2026 |
| Maths & Science.Com Ltd | Education | 2014 |
| Matrix 365 Limited | Other services | 2020 |
| Matrix Talents Ltd | Administrative & support | 2024 |
| Matru Limited | Wholesale & retail | 2026 |
| Matts BBQ Community CIC | Health & social care | 2026 |
| Matts BBQ Limited | Hospitality | 2017 |
| Mattwoi Ltd | Wholesale & retail | 2025 |
| Matys Property Ltd | Real estate | 2018 |
| MAV Bearings Ltd | Manufacturing | 2024 |
| MAW Contracting Ltd | Administrative & support | 2025 |
| MAX Matrix Services Limited | Wholesale & retail | 2016 |
| Maxar Services Ltd | Wholesale & retail | 2023 |
| Maxdan Limited | Construction | 2018 |
| Maximoor CIS Limited | Professional & scientific | 2018 |
| Maximum Autos Ltd | Wholesale & retail | 2024 |
| Maxin Chicken & Ribs Ltd | Hospitality | 2025 |
| Maxin Kebab Chicken Pizza & Ribs Limited | Hospitality | 2022 |
| Maxin Pizza Limited | Hospitality | 2025 |
| Maxworld Media Ltd | Information & communication | 2026 |
| Maxworld Properties Ltd | Real estate | 2015 |
| Maxyink & Stuff (UK) Limited | Administrative & support | 2010 |
| MAY the First Limited | Information & communication | 2015 |
| Mayowa Foods Ltd | Wholesale & retail | 2024 |
| Mayunga Books Limited | Information & communication | 2024 |
| Mayunga Enterprises Ltd | Financial services | 2022 |
| Mayunga Group Ltd | Financial services | 2026 |
| Mayunga IP Ltd | Administrative & support | 2026 |
| Mayzon Limited | Other services | 2023 |
| Mazda Motors UK Limited | Wholesale & retail | 2001 |
| MB Boxing Ltd | Arts & recreation | 2023 |
| MB Hale Consultancy Ltd | Professional & scientific | 2015 |
| MB Labour Force Ltd | Construction | 2024 |
| MBE Real Estates Limited | Real estate | 2021 |
| MBG Contractors Ltd | Other services | 2008 |
| Mbgriffiths Consultancy Ltd. | Professional & scientific | 2017 |
| MBR Smart Repairs Limited | Transport & logistics | 2015 |
| MC Alpha Consult Limited | Professional & scientific | 2009 |
| MC Care Services Ltd | Administrative & support | 2017 |
| MC Tech Services Limited | Wholesale & retail | 2021 |
| Mc's Hair & Nails Ltd | Other services | 2025 |
| Mc-Crystal Limited | Administrative & support | 2010 |
| MCA Garage Services Ltd. | Wholesale & retail | 2015 |
| Mcaden Limited | Real estate | 2021 |
| Mcallisters Transport Ltd | Administrative & support | 2016 |
| Mccade Hire Ltd | Administrative & support | 2010 |
| Mccarthy Services Limited | Construction | 1997 |
| MCD Sprint Consultancy Ltd | Professional & scientific | 2017 |
| Mcfeley Development Associates Ltd | Real estate | 2024 |
| Mcharris Estates Ltd | Financial services | 2024 |
| Mcharris Limited | Wholesale & retail | 2020 |
| Mchope Properties Ltd | Real estate | 2021 |
| Mckees Design and Build Limited | Construction | 2026 |
| Mckenna Building Contractors Limited | Construction | 1995 |
| Mckenna Properties and Investments Ltd | Real estate | 2023 |
| Mclaren Driveways Limited | Construction | 2019 |
| Mcmillan Delon Limited | Manufacturing | 2024 |
| Mcmurphy's Consult Ltd | Professional & scientific | 2016 |
| Mcnamara Freight Holdings Limited | Professional & scientific | 2005 |
| Mcnamara Freight Limited | Transport & logistics | 1990 |
| Mcsengineers Ltd | Professional & scientific | 2024 |
| MD Delwer Hossain Limited | Transport & logistics | 2025 |