| Mobile Fusion Limited | Wholesale & retail | 2019 |
| Mobility 1 Limited | Information & communication | 2026 |
| Mobility Solutions (South) Ltd | Other services | 2010 |
| Modeluxe Management Limited | Professional & scientific | 2025 |
| Modernmoneybooks Limited | Wholesale & retail | 2023 |
| Modest Social Care Ltd | Health & social care | 2022 |
| Mokech Ltd | Health & social care | 2023 |
| Molam Property Services Ltd | Real estate | 2022 |
| Molimic Ltd | Administrative & support | 2021 |
| Monarch Removals Limited | Transport & logistics | 2017 |
| Money Tree Films Ltd | Information & communication | 2018 |
| Monica&Arnold Ltd | Transport & logistics | 2024 |
| Monkey PEN Ltd | Information & communication | 2019 |
| Monkwood Close Airspace 1 Limited | Real estate | 2022 |
| Montagna Property Partners Limited | Real estate | 2018 |
| Monte Portuguese Cafe Restaurant Ltd | Hospitality | 2016 |
| Montrose Care Home Ltd | Health & social care | 2017 |
| Montrose Glass Limited | Construction | 2012 |
| Mooboo Southend Limited | Wholesale & retail | 2024 |
| Moods Hospitality & Catering Ltd | Hospitality | 2019 |
| Moon Light Bar and Restaurant Limited | Hospitality | 2023 |
| Moonchambers Limited | Administrative & support | 2019 |
| Moonleaf Design Limited | Professional & scientific | 2026 |
| Moonlit Auria Ltd | Health & social care | 2025 |
| Moorfield Way (Wilberfoss) Management Company Limited | Households | 2016 |
| Mopic Limited | Information & communication | 2025 |
| More Clicks Ltd | Information & communication | 2019 |
| Moreas Venture Ltd | Wholesale & retail | 2025 |
| Morf Global Limited | Financial services | 2019 |
| Morgan Dakin Homes Limited | Construction | 2001 |
| Morgan’S Mobile Foot Care Ltd | Other services | 2017 |
| Morleys Music Ltd | Wholesale & retail | 2022 |
| Morleys Studios Ltd | Real estate | 2025 |
| Mortgage Friendly.Net Limited | Financial services | 2000 |
| Mortgage House Services Ltd | Financial services | 2019 |
| Mortgages DOT Online Limited | Financial services | 2018 |
| Morton & Yeates Limited | Hospitality | 2012 |
| Morttcorp Ltd | Wholesale & retail | 2016 |
| Morven Group Ltd | Professional & scientific | 2021 |
| MOS Beauty Ltd | Wholesale & retail | 2018 |
| Mosman Capital Ltd | Real estate | 2011 |
| Moswa Ltd. | Health & social care | 2019 |
| Motacar Ltd | Wholesale & retail | 2014 |
| Motherhood Made Simple Ltd | Administrative & support | 2025 |
| Motor & Armature Rewinds Limited | Manufacturing | 1968 |
| Motus Property Maintenance Ltd | Professional & scientific | 2016 |
| Mount Street Mews Design Limited | Real estate | 2022 |
| Mount Sunshine Property Limited | Real estate | 2025 |
| Mountain Drip Ltd | Hospitality | 2024 |
| Mountain Property Limited | Real estate | 2006 |
| Mountstephens Sports Marketing Limited | Professional & scientific | 2020 |
| Mountview Aviation Consultants Ltd | Financial services | 2016 |
| Move Online Essex Limited | Real estate | 2016 |
| Moving Mindspace Limited | Health & social care | 2025 |
| Moyet GAS Services Limited | Construction | 2014 |
| Moylans (Holdings) Limited | Financial services | 2021 |
| Moylans Group Holdings Limited | Financial services | 2026 |
| Mozep Services Ltd | Health & social care | 2020 |
| MPC Digital Ltd | Professional & scientific | 2026 |
| MPR Transport Ltd | Transport & logistics | 2024 |
| MR Simms Quays Outlet Ltd | Wholesale & retail | 2025 |
| MR Simms Southend-On-Sea Ltd | Wholesale & retail | 2025 |
| Mrahman Consultants Limited | Professional & scientific | 2018 |
| MRS Walker Limited | Financial services | 2019 |
| MS Property Services Group Ltd | Construction | 2024 |
| MSB Global Group Limited | Information & communication | 2025 |
| MSB Southend Ltd | Professional & scientific | 2023 |
| MSD National Ltd | Other services | 2016 |
| MSE Housing Limited | Real estate | 2024 |
| MSM Partners Limited | Extraterritorial | 2015 |
| Mssv Group Ltd | Wholesale & retail | 2023 |
| MSV Developments Limited | Construction | 2004 |
| Mtaem Consultancy Services Limited | Professional & scientific | 2012 |
| MTM Vision Ltd | Professional & scientific | 2018 |
| Muchemeyi Reporting Ltd | Health & social care | 2021 |
| Muesli Limited | Professional & scientific | 2025 |
| Muirway Management Company Limited | Households | 1989 |
| Mujtaba Limited | Health & social care | 2023 |
| Mukmin Limited | Hospitality | 2026 |
| Mulberry (North Bersted) Management Company Limited | Households | 2018 |
| Mulberry Field Ltd | Financial services | 2025 |
| Mulberry Grange (Castleford) Management Company Limited | Households | 2018 |
| Mulberry Property Investments (SE) Ltd | Real estate | 2023 |
| Muller & King Ltd | Extraterritorial | 2012 |
| Multani Real Estate Ltd | Real estate | 2025 |
| Multi Ethnic Running Club CIC | Arts & recreation | 2024 |
| Multi-Skilled Contractors Ltd | Construction | 2020 |
| Multiform Global Ltd | Wholesale & retail | 2025 |
| Multiform Machinery Limited | Manufacturing | 2019 |
| Multiport Services Ltd | Transport & logistics | 2016 |
| Murrays Communications Ltd | Professional & scientific | 2020 |
| Musa Kamaly Limited | Hospitality | 2019 |
| Muscle Yard Gyms Limited | Arts & recreation | 2025 |
| Mushie-It Ltd | Professional & scientific | 2026 |
| Muss Group Limited | Administrative & support | 2023 |
| MW AQA Ltd | Financial services | 2016 |
| MW Land Developments Limited | Construction | 2017 |
| MXG Holding Limited | Financial services | 2025 |
| My Cinema Limited | Wholesale & retail | 2009 |
| My Fashion HUT Limited | Wholesale & retail | 2022 |