| Mercury Executives Ltd | Transport & logistics | 2025 |
| Mercury Safety & Security Group Limited | Manufacturing | 2006 |
| Merg Consulting Ltd | Professional & scientific | 2009 |
| Merisant UK Limited | Manufacturing | 2000 |
| Meris’Ice Cream Limited | Hospitality | 2025 |
| Merlen Limited | Wholesale & retail | 2022 |
| Merlin Auto Services Limited | Wholesale & retail | 2008 |
| Merlings Investments Ltd | Real estate | 2022 |
| Merovyn Ltd | Information & communication | 2026 |
| Merrivale Developments Limited | Construction | 2016 |
| Merry Estates Ltd | Real estate | 2021 |
| Merry Go Round Development Limited | Information & communication | 2025 |
| Meru Publishing Limited | Information & communication | 2015 |
| Meshhh Interiors Ltd | Construction | 2023 |
| Mesopotamia Security Services Ltd | Financial services | 2025 |
| Messy Brushes Ltd | Construction | 2022 |
| Metamorph Advisory Partners Ltd | Administrative & support | 2022 |
| Metamorph Development Ltd | Real estate | 2021 |
| Meter X Limited | Administrative & support | 2012 |
| Methexis Limited | Professional & scientific | 2019 |
| Metis Clinical Value Advisory Ltd | Professional & scientific | 2026 |
| Metro Fresh Superstore Ltd | Wholesale & retail | 2023 |
| MF (GBY) Ltd | Wholesale & retail | 2019 |
| MFA Electrical Ltd | Construction | 2012 |
| MFT Holdings Ltd | Administrative & support | 2015 |
| MG Apartment Ltd | Real estate | 2024 |
| MG Carpentry & Joinery Ltd | Manufacturing | 2019 |
| MG Cuisine Ltd | Hospitality | 2026 |
| MG Global Consulting Limited | Professional & scientific | 2022 |
| MG Immigration Services Ltd | Other services | 2021 |
| MGI UK Area Limited | Other services | 2006 |
| MGM Advisors Ltd | Professional & scientific | 2023 |
| Mgrs Ltd | Wholesale & retail | 2009 |
| MH Central Ltd | Real estate | 2022 |
| MH EXP Ltd | Wholesale & retail | 2020 |
| MH Financial Consulting Limited | Information & communication | 2023 |
| MH Property and Land Ltd | Real estate | 2014 |
| MH QTM Ltd | Professional & scientific | 2025 |
| MHA HW Motors Ltd | Wholesale & retail | 2026 |
| MHD Property Limited | Real estate | 2019 |
| Mhere Project Consultancy Ltd | Professional & scientific | 2018 |
| MHJ (1989) Limited | Professional & scientific | 2005 |
| Mhma Property Services Limited | Real estate | 2022 |
| Mhodge Ltd | Construction | 2018 |
| MHS Estates Limited | Real estate | 2014 |
| MHS Land and Homes Ltd | Construction | 2018 |
| MIA Madeleine Investments Unlimited | Financial services | 2025 |
| MIA Mira Ltd | Other services | 2025 |
| Miandistribution Ltd | Transport & logistics | 2021 |
| MIB Express Ltd | Other services | 2025 |
| Michael Dixson Property Services Limited | Construction | 2010 |
| Michael Hewitt Associates LLP | | 2011 |
| Michael Platt Limited | Wholesale & retail | 2010 |
| Micklefield Motors Ltd | Wholesale & retail | 2015 |
| Micro Pods UK Ltd | Health & social care | 2024 |
| Micro Solve (Hygiene) Limited | Other services | 1995 |
| Microbe Investments Ltd | Hospitality | 2015 |
| Microbit Technologies Ltd | Information & communication | 2012 |
| Microtech Electronics Limited | Manufacturing | 1974 |
| Microtech Electronics Management Ltd | Professional & scientific | 2006 |
| Microtechnic Electronics Ltd | Administrative & support | 2005 |
| MID Production Ltd | Manufacturing | 2024 |
| MID Property HW Ltd | Real estate | 2025 |
| MID Summer Taxis Limited | Transport & logistics | 2026 |
| Midas Events Management Ltd | Hospitality | 2021 |
| Midnight Circle Ltd | Wholesale & retail | 2025 |
| Midtown Music Education Ltd | Extraterritorial | 2011 |
| Midtown Music Ltd | Other services | 2011 |
| MIG Private Limited | Manufacturing | 2025 |
| Mighty Meaty Ltd | Hospitality | 2024 |
| Mikado Foods (UK) Ltd | Wholesale & retail | 2011 |
| Mike Curtis and Company Limited | Professional & scientific | 2023 |
| Mike Walker Academy Limited | Arts & recreation | 2006 |
| Mike Wallington Plumbing & Heating Limited | Construction | 2015 |
| Miledawn Limited | Construction | 2000 |
| Milestone Creative Employee Trustee Limited | Extraterritorial | 2023 |
| Milestone Creative Limited | Professional & scientific | 1995 |
| Mill END Close Limited | Households | 2003 |
| Mill House Wooburn Ltd | Real estate | 2024 |
| Mill Lane Holdings Ltd | Professional & scientific | 2024 |
| Miller Supported Housing CIC | Health & social care | 2025 |
| Millers Brow Management Company Ltd | Extraterritorial | 2008 |
| Millside Services Ltd | Real estate | 2024 |
| Millstone Property Ltd | Construction | 2017 |
| Millstream Technology Ltd | Information & communication | 2024 |
| Mimosa Garden Services Limited | Other services | 2023 |
| Mind Bliss Therapies Ltd | Health & social care | 2024 |
| Mind Body Active Ltd | Arts & recreation | 2025 |
| Mind Body Alchemy Limited | Arts & recreation | 2026 |
| Mind Strong Hub Ltd | Professional & scientific | 2025 |
| MIND4IT Ltd | Information & communication | 2013 |
| Mindbridge Bucks CIC | Health & social care | 2026 |
| Mindcraft Education Ltd | Education | 2024 |
| Mindforge Advisory Ltd | Information & communication | 2026 |
| Mindful Living Solutions Ltd | Health & social care | 2025 |
| Mindful Support Ltd | Public administration | 2025 |
| Mindful Voice Collective Limited | Arts & recreation | 2023 |
| Mindsculptors Ltd | Professional & scientific | 2023 |
| Mindsinsync Limited | Wholesale & retail | 2005 |
| Mindsnaps CIC | Education | 2024 |