| Mastermind Consulting Services Ltd | Administrative & support | 2017 |
| Mastermind Property Services Limited | Real estate | 2019 |
| Masthead Communications Limited | Professional & scientific | 2020 |
| Material Supply Solutions Limited | Wholesale & retail | 2021 |
| Matlbuchananconsultancy Ltd | Administrative & support | 2025 |
| Matloch Medical Services Limited | Health & social care | 2024 |
| Matrix Commercial Property Ltd | Real estate | 2021 |
| Matt Dixon Security Specialist Limited | Administrative & support | 2026 |
| Matt Edney & Co Drylining Ltd | Other services | 2019 |
| Matt Muir Ltd | Professional & scientific | 2016 |
| Matteo World (UK) Ltd | Administrative & support | 2017 |
| Matters Media Limited | Professional & scientific | 1987 |
| Maura L.M Limited | Health & social care | 2023 |
| Maven Design Studio Limited | Professional & scientific | 2017 |
| MAW Property Lettings Limited | Real estate | 2019 |
| Maxiload Limited | Wholesale & retail | 2023 |
| Maxorella Limited | Professional & scientific | 2009 |
| Maya Search Limited | Professional & scientific | 2011 |
| Mayfair Estates Property Investment and Funding Ltd | Real estate | 2010 |
| Mays Soft Play Ltd | Arts & recreation | 2024 |
| MB Carpentry Hampshire Ltd | Construction | 2026 |
| MB Garage Services Ltd | Professional & scientific | 2015 |
| MB Publications Ltd | Information & communication | 2024 |
| MB Valets Limited | Administrative & support | 2025 |
| MBB Installations Ltd | Construction | 2025 |
| MBC Technical Ltd | Wholesale & retail | 2015 |
| Mbha Services Limited | Transport & logistics | 2017 |
| MBJ Jerk HUT Limited | Hospitality | 2025 |
| MBT Industries Ltd | Administrative & support | 2021 |
| MC Architectural Design Limited | Professional & scientific | 2021 |
| MC Cars Waterlooville Ltd | Other services | 2014 |
| MC Health Consulting Ltd | Professional & scientific | 2023 |
| MC Plastering & Building Ltd | Construction | 2026 |
| Mcad Global Limited | Financial services | 2022 |
| MCB Contracting Services Limited | Wholesale & retail | 2023 |
| Mcbride Designs Limited | Information & communication | 1997 |
| Mccallum BEE Limited | Professional & scientific | 2013 |
| Mccoys Property Ltd | Real estate | 2025 |
| MCD Building Ltd | Construction | 2011 |
| Mcdonald Homecare Ltd | Health & social care | 2018 |
| Mcdowall Holdings Limited | Financial services | 2012 |
| Mcfarland Independent Contractors Ltd | Professional & scientific | 2023 |
| Mcglone Medical Services Limited | Health & social care | 2018 |
| Mcgrill Associates Ltd | Administrative & support | 2026 |
| Mckean Contractors Holdings Limited | Financial services | 2016 |
| Mckean Contractors Limited | Construction | 2012 |
| Mckeand Property Limited | Real estate | 2020 |
| Mckinsey Management Services Limited | Professional & scientific | 2018 |
| Mckw Ltd | Real estate | 2025 |
| MCM Households Ltd | Real estate | 2024 |
| Mcmenemy Consulting Ltd | Professional & scientific | 2025 |
| MCR Spotlight Limited | Information & communication | 2025 |
| MCS Motor Company / Photography Ltd | Wholesale & retail | 2006 |
| Mcsa Cafe Holdings Ltd | Hospitality | 2011 |
| MD & Partners Ltd | Information & communication | 2023 |
| MD Electrical Services Southern Ltd | Construction | 2025 |
| MDE1 Limited | Real estate | 2021 |
| MDE2 Limited | Real estate | 2021 |
| Mdepot Limited | Wholesale & retail | 2021 |
| MDT Medical Limited | Health & social care | 2022 |
| ME Collective Limited | Other services | 2023 |
| Meadowgate Groundworks & Build Limited | Construction | 2026 |
| Measured HS Ltd | Professional & scientific | 2023 |
| Media Connect Ltd | Transport & logistics | 2023 |
| Media Meerkat Ltd | Professional & scientific | 2021 |
| Medicue UK Ltd | Information & communication | 2024 |
| Medimark Group Limited | Wholesale & retail | 2020 |
| Mediprime Limited | Health & social care | 2017 |
| Medisthetics Engineering Ltd | Manufacturing | 2024 |
| Medska Limited | Professional & scientific | 2024 |
| Meeview Limited | Information & communication | 2025 |
| Megabeast Games Limited | Manufacturing | 2025 |
| Mehiel.Io Limited | Professional & scientific | 2025 |
| MEI Kitchen Ltd | Hospitality | 2023 |
| Melfield Property Company Limited | Real estate | 1963 |
| Melfield Property Services Limited | Real estate | 2005 |
| Memc Consulting Limited | Other services | 2018 |
| Memorable Moments Collective Ltd | Manufacturing | 2025 |
| Menon Radiology Services Limited | Health & social care | 2022 |
| Menu Dash Limited | Information & communication | 2020 |
| Meon Consultants Ltd | Administrative & support | 2019 |
| Meon Valley Financial Planning Limited | Financial services | 1997 |
| Meon Valley Pets Limited | Wholesale & retail | 2026 |
| Meon Valley Rackers Ltd | Manufacturing | 2024 |
| Mercer Pubco Ltd | Hospitality | 2015 |
| Merch Bubble Limited | Financial services | 2019 |
| Merchant Lane Limited | Manufacturing | 2005 |
| Merchants Wealth Management Limited | Financial services | 2014 |
| Mercury Management Services (UK) Ltd | Information & communication | 2008 |
| Meredith Lodge RTM Company Limited | Households | 2021 |
| Merida Foods Ltd | Wholesale & retail | 2026 |
| Meridian General Cleaning Ltd | Other services | 2016 |
| Meringtons Workshop Limited | Other services | 2006 |
| Merriott Holdings Limited | Financial services | 2016 |
| Merrymeme Limited | Financial services | 2024 |
| MES Engineering Solutions Ltd | Professional & scientific | 2025 |
| Mesh Property Services Ltd | Construction | 2015 |
| Meso and More Training Academy Ltd | Education | 2021 |
| Metabolic Health Training Limited | Health & social care | 2022 |
| Metacast Ltd | Information & communication | 2024 |