| Mccoys PUB Brokers Limited | Administrative & support | 2000 |
| Mccullough Engineering Limited | Administrative & support | 2008 |
| Mckenzie Feeds Limited | Manufacturing | 1973 |
| Mclaren Past Personnel Association | Other services | 2024 |
| Mclean Quinlan Ltd | Professional & scientific | 2019 |
| Mcmorris Developments Limited | Real estate | 1963 |
| Mcmorris Investments Limited | Professional & scientific | 2008 |
| Mcmorris Properties Limited | Real estate | 2010 |
| Mcnaughts Surveyors Limited | Professional & scientific | 2015 |
| Mcneill Heating Limited | Construction | 2017 |
| Mcqueen Management Limited | Real estate | 2015 |
| MD Renovation & Refurb Limited | Construction | 2024 |
| MD Winchester Ltd | Hospitality | 2025 |
| MDT Rehab Limited | Health & social care | 2023 |
| ME Estimating & Engineering Limited | Professional & scientific | 2015 |
| Meacher Nisbet Limited | Real estate | 2016 |
| Meadow Farm Limited | Agriculture & fishing | 2002 |
| Meadow Rise Management Company Limited | Households | 2010 |
| Meadowlands Residents Management Company Limited | Households | 2020 |
| Measuremen Limited | Professional & scientific | 2016 |
| Med-Ak ENT Services UK Ltd | Health & social care | 2019 |
| Medi's Vintage Ltd | Wholesale & retail | 2023 |
| Medical Affairs 360 Ltd | Professional & scientific | 2020 |
| Medical GAS Pipelines Ltd | Construction | 2006 |
| Medical Support Solutions Limited | Health & social care | 2003 |
| Medicolegal & Abdominal Radiology Limited | Transport & logistics | 2014 |
| Medisafe Limited | Manufacturing | 1998 |
| Medtech Economics Ltd. | Professional & scientific | 2015 |
| Medtech Mastery Ltd | Professional & scientific | 2022 |
| Medvest Technologies UK LLP | | 2018 |
| Medvest UK LLP | | 2007 |
| Meerkat Music Limited | Arts & recreation | 2004 |
| Megan Lloyd-Davies Limited | Professional & scientific | 2006 |
| Megapost Ltd | Information & communication | 2026 |
| Meguire Estates Limited | Real estate | 2026 |
| Mehri Publication Ltd | Wholesale & retail | 2017 |
| Meikle Advisers Limited | Real estate | 2014 |
| Melek Limited | Real estate | 1999 |
| Melhuish Limited | Extraterritorial | 2015 |
| Melirick Ltd | Professional & scientific | 2025 |
| Melissa Corfield Consulting Limited | Other services | 2016 |
| Mellowhouse Limited | Construction | 1984 |
| Memorable Marketing Limited | Extraterritorial | 2010 |
| Memories Captured Ltd | Arts & recreation | 2021 |
| Meneghini Ltd | Professional & scientific | 2024 |
| Meon Accountancy Services Limited | Professional & scientific | 2014 |
| Meon Accounting Limited | Professional & scientific | 2004 |
| Meon Project Services (MPS) Limited | Professional & scientific | 2017 |
| Meon Valley Estates Limited | Real estate | 1988 |
| Mercatura Carsales Ltd | Wholesale & retail | 2019 |
| Mercurie UK Limited | Information & communication | 2024 |
| Mercurry Inns Ltd | Hospitality | 2013 |
| Mercury Homesearch Limited | Real estate | 2010 |
| Meridian Metal Roofing Ltd | Manufacturing | 2002 |
| Merita Ltd | Professional & scientific | 2025 |
| Merlin Accessories Limited | Wholesale & retail | 1979 |
| Merlin Lawn Care Limited | Administrative & support | 2024 |
| Merlion Capital Corporation Limited | Real estate | 2001 |
| Merlion Capital Holdings Limited | Real estate | 2015 |
| Merlion Capital Investments Limited | Real estate | 2015 |
| Merlion Capital Partners Ltd | Real estate | 2010 |
| Mermaids Fish Bar Limited | Hospitality | 2022 |
| Merry Matthews Land Services Limited | Administrative & support | 2011 |
| Mervyn's Coaches Ltd | Transport & logistics | 2025 |
| Mervyn's Tours Ltd | Administrative & support | 2025 |
| Metaip Consultancy Limited | Information & communication | 2023 |
| Metallum Ltd | Information & communication | 2018 |
| Metamichi Limited | Information & communication | 2003 |
| Metanava Limited | Information & communication | 2025 |
| Metastream Limited | Professional & scientific | 2018 |
| Mexigo Consulting Ltd | Professional & scientific | 2014 |
| Meywood Ltd | Information & communication | 2022 |
| MF Medical Ltd | Health & social care | 2022 |
| MG Propserve Limited | Professional & scientific | 2022 |
| MHE Consultants International Ltd | Wholesale & retail | 2022 |
| MHT Flat Roofing Limited | Construction | 2016 |
| Mhtg Property Limited | Real estate | 2024 |
| Mi&Corr Limited | Mining & quarrying | 2010 |
| Michael Blake Carpentry Ltd | Manufacturing | 2025 |
| Michael Sinclair Studio Limited | Professional & scientific | 2016 |
| Michele White Limited | Real estate | 2020 |
| Microbiological Supply Company Ltd | Wholesale & retail | 2019 |
| Micromuse Limited | Information & communication | 1988 |
| Micromuse U K Holdings Limited | Professional & scientific | 2002 |
| Micronic Microphones Limited | Manufacturing | 2024 |
| MID Devon Tyres Limited | Extraterritorial | 2003 |
| MID Hampshire Healthcare Limited | Health & social care | 2014 |
| MID Hants Fire Protection Ltd | Other services | 2017 |
| Middle Orchard Management Limited | Households | 2024 |
| Midus Global Mining Limited | Administrative & support | 2021 |
| Midus Holdings Limited | Administrative & support | 2017 |
| Mike Caldwell Photography Limited | Professional & scientific | 2002 |
| Mike Dyer Mediation & Consultancy Ltd | Professional & scientific | 2013 |
| Mike Henry Electrical Contractors Limited | Construction | 2017 |
| Mill House Restaurants Limited | | 1989 |
| Mill Place (Overton Road) Management Company Limited | Households | 2006 |
| Mill Stream Property Ltd | Construction | 2017 |
| Millar Equine Vets Limited | Professional & scientific | 2023 |
| Milleon Ltd | Professional & scientific | 2025 |
| Miller & Cain Holdings Limited | Water & waste | 2019 |