| Metro Gold Limited | Extraterritorial | 2016 |
| Metro Monitoring Ltd | Construction | 2012 |
| Metropolitan Police Sailing Club Ltd | Arts & recreation | 2005 |
| Mexifun Limited | Hospitality | 2020 |
| Mexigo Burrito Bar Ltd | Administrative & support | 2015 |
| Mexrose Limited | | 1979 |
| MF Plumbing Solutions Ltd | Construction | 2025 |
| Mf.Property.Investments. Ltd | Real estate | 2024 |
| Mfdland Limited | Real estate | 2019 |
| MFR South Consulting Limited | Information & communication | 2024 |
| MG Electrical (Southern) Ltd | Construction | 2017 |
| MG Finance Ltd | Financial services | 2013 |
| MG Football Consultancy Ltd | Other services | 2024 |
| MG Hospitality Ltd | Hospitality | 2017 |
| MG Hotels & Resorts Ltd | Real estate | 2006 |
| MG Media Group Ltd | Professional & scientific | 2020 |
| MG Mini Mart Limited | Wholesale & retail | 2025 |
| MG Probuild Ltd | Construction | 2025 |
| MG Property Investments Ltd | Real estate | 2015 |
| MG Real Estate Ltd | Real estate | 2026 |
| MG Solar Ltd | Construction | 2023 |
| MG Source Ltd | Professional & scientific | 2026 |
| MG80 Car Hire Limited | Administrative & support | 2022 |
| MG80 Limited | Wholesale & retail | 2019 |
| MGI Transport Ltd | Transport & logistics | 2019 |
| Mgif Consulting Ltd | Information & communication | 2018 |
| MGJ Carpentry Services Ltd | Manufacturing | 2023 |
| MGN Inventories Ltd | Administrative & support | 2017 |
| MGR Properties Ltd | Real estate | 2022 |
| Mgry Ltd | Wholesale & retail | 2026 |
| MGS Landscaping Services Ltd | Administrative & support | 2024 |
| Mgts E Bikes Ltd | Wholesale & retail | 2025 |
| MH Gajjar Ltd | Transport & logistics | 2026 |
| MH Joinery Holdings Limited | Professional & scientific | 2020 |
| MH3 Plumbing and Heating (Southern) Limited | Construction | 2015 |
| MHB Property Services Ltd | Households | 2024 |
| MHJ Diamond Used Car and Auto Parts Ltd | Wholesale & retail | 2023 |
| MHK Draughting Services Limited | Construction | 2007 |
| Mhkan Limited | Real estate | 2020 |
| Mhluxtaxi Ltd | Transport & logistics | 2019 |
| Mhplus Limited | Health & social care | 2018 |
| MHS Delivery Ltd | Transport & logistics | 2025 |
| Mhws Equipment Limited | Professional & scientific | 2010 |
| MI (Bellemoor) Property Limited | Administrative & support | 2016 |
| MI Middle Solutions Ltd | Transport & logistics | 2026 |
| MI Rice Limited | Hospitality | 2019 |
| MIA Bathrooms Ltd | Construction | 2012 |
| MIA Boardman Ltd | Professional & scientific | 2021 |
| Mia-Louise Hair Extensions Ltd | Other services | 2025 |
| Miah Engineering Ltd | Professional & scientific | 2024 |
| Miahology Ltd | Health & social care | 2021 |
| Miami Supplements Southampton Ltd | Wholesale & retail | 2022 |
| Miami UK Ltd | Information & communication | 2025 |
| Miaomiaouk Ltd | Wholesale & retail | 2023 |
| Miatec Construction Limited | Wholesale & retail | 2017 |
| Miatec Holdings Limited | Wholesale & retail | 2016 |
| MIC Enterprises Ltd | Construction | 2025 |
| Micank Limited | Transport & logistics | 2019 |
| Micdrops Beverages Limited | Manufacturing | 2025 |
| Michael and Judith Cummings Limited | Health & social care | 2017 |
| Michael J. Dant Management LLP | | 2007 |
| Michael Kenway Ltd | Administrative & support | 2025 |
| Michael Patrick Homes Limited | Real estate | 2021 |
| Michael Samuels Property Ltd | Real estate | 2023 |
| Michael Schmidt & Partner Limited | Wholesale & retail | 2002 |
| Michael Starling Consultancy Ltd | Professional & scientific | 2016 |
| Michael Todd Plumbing & Heating Ltd | Construction | 2006 |
| Michaela Wood Ltd | Real estate | 2023 |
| Michaelmas Place (Swanmore) Limited | Households | 2008 |
| Michaels Recycles Limited | Wholesale & retail | 2014 |
| Michela Trans Ltd | Transport & logistics | 2024 |
| Michelle's Homemade Kitchen Limited | Hospitality | 2025 |
| Michelle's New Forest Bakes Limited | Financial services | 2025 |
| Michelle's New Forest Kitchen Ltd | Hospitality | 2025 |
| Michie Care Private Ltd | Health & social care | 2021 |
| Miciamiao Ltd | Wholesale & retail | 2025 |
| Mickeyjcomposites Ltd | Manufacturing | 2022 |
| Micks Motor Repairs and Tyres. Limited | Manufacturing | 2013 |
| Miclee Solutions Ltd | Manufacturing | 2020 |
| Micro Soulutions Limited | Administrative & support | 2026 |
| Microseo Ltd | Administrative & support | 2017 |
| Microtree Limited | Health & social care | 2022 |
| Midanbury Court Residents Association Ltd | Households | 2025 |
| Midanbury Maintenance Ltd | Construction | 2024 |
| Middle Brook Management Ltd | Households | 2001 |
| Middle Road Management Company Limited | Households | 2009 |
| Middletons Property Ltd | Real estate | 2020 |
| Midknight Properties Ltd | Hospitality | 2025 |
| Midline Design Limited | Professional & scientific | 2023 |
| Midnight Health Limited | Professional & scientific | 2022 |
| Midnight JAX Capital Ltd | Financial services | 2026 |
| Midnight Lady Limited | Wholesale & retail | 2004 |
| Midship Boat Services Limited | Manufacturing | 1981 |
| Mighall Consulting Ltd | Real estate | 2021 |
| Mighty Acorn Anglo-American Limited | Hospitality | 2001 |
| Mighty Stone Food & Drink Limited | Hospitality | 2010 |
| Mignonette Kennels Limited | Agriculture & fishing | 2020 |
| Miguel's Plant Operations Ltd | Construction | 2018 |
| MIK Properties Ltd | Real estate | 2023 |
| Mikan Tattoo Limited | Other services | 2024 |