| M.J Inns Limited | Hospitality | 2019 |
| M.J. & a. Accountancy Services Limited | Professional & scientific | 2015 |
| M.J. Neal Limited | Wholesale & retail | 1996 |
| M.J.T. Security Service Ltd. | Administrative & support | 2012 |
| M.P.H. Bodyshop Limited | Wholesale & retail | 2007 |
| M.Sheard E & I Limited | Professional & scientific | 2021 |
| M.Young.Solutions Limited | Professional & scientific | 2021 |
| M2O Plumbing Limited | Construction | 2017 |
| M2S Canopy Supply Ltd | Manufacturing | 2025 |
| M3 Estate Agents Limited | Real estate | 2025 |
| MA Aviation Ltd | Professional & scientific | 2012 |
| MAB Consultancy Services Limited | Administrative & support | 2012 |
| MAC Glazing Specialist Ltd | Construction | 2026 |
| Macaulay Area Action Group | Arts & recreation | 2002 |
| Machine Networks Limited | Information & communication | 2005 |
| Mack Construction and Developments Ltd | Construction | 2017 |
| Madalin Logistic Ltd | Transport & logistics | 2025 |
| Made Great in Grimsby Limited | Administrative & support | 2019 |
| Made to Measure Joinery Grimsby Limited | Manufacturing | 2015 |
| Made to Measure Window Systems Limited | Manufacturing | 2004 |
| Madras Curry House Ltd | Hospitality | 2019 |
| MAF Projects Limited | Construction | 2011 |
| Magba Consultancy Limited | Construction | 2024 |
| Mager Homes Limited | Construction | 1980 |
| Magic Caterpillar Ltd | Professional & scientific | 2017 |
| Magic Sparkle Pony Limited | Real estate | 2023 |
| Magicmugs Ltd | Administrative & support | 2016 |
| Magnum Carter Holdings Ltd | Financial services | 2022 |
| Magnum Motorhome and Caravan Supplies Limited | Manufacturing | 2003 |
| Maha Group Ltd | Wholesale & retail | 2017 |
| Maha Retail Store Limited | Wholesale & retail | 2023 |
| Mainserve Contracts Limited | Construction | 2003 |
| Maintainance Masters Ltd | Administrative & support | 2024 |
| Maison Letting Limited | Real estate | 2023 |
| Maison Rouge Limited | Wholesale & retail | 2014 |
| Majorpro Ltd | Wholesale & retail | 2019 |
| Make Them Smile | Other services | 2011 |
| Making Banana Bread Ltd | Wholesale & retail | 2025 |
| Makkah Experience Ltd | Wholesale & retail | 2026 |
| Makoki Ltd | Wholesale & retail | 2022 |
| Maleva Market Limited | Wholesale & retail | 2025 |
| Malgar Fish Company Limited | Administrative & support | 2002 |
| Maliks & Khan ESTATES1 Ltd | Real estate | 2024 |
| Mallam Invest Ltd | Construction | 2013 |
| Malou Associates Ltd | Construction | 2013 |
| Maltings Way Management Limited | Administrative & support | 2001 |
| Malvern Heating Limited | Construction | 2023 |
| Management Systems Advisory Services Limited | Professional & scientific | 2003 |
| Manby Road Service Station Ltd | Wholesale & retail | 2022 |
| Manchester Mends Ltd | Construction | 2019 |
| Mandy's Pantry CIC | Education | 2024 |
| Mann & Burton Consultancy Limited | Wholesale & retail | 2004 |
| Manor Carpentry & Construction Limited | Construction | 2006 |
| Manshack Limited | Wholesale & retail | 2016 |
| Manson Timber Engineering Limited | Professional & scientific | 2003 |
| Mantel Design Ltd | Professional & scientific | 2019 |
| Manx (UK) Limited | Other services | 2010 |
| MAP Properties and Services Limited | Households | 2019 |
| Mapec Limited | Professional & scientific | 2016 |
| Maple Towing and Leisure Ltd | Wholesale & retail | 2021 |
| Maple Trailer Hire Ltd | Administrative & support | 2022 |
| Marble Graphics Limited | Administrative & support | 2000 |
| Marcibt Ltd | Transport & logistics | 2025 |
| Marcin Alex Ltd | Transport & logistics | 2012 |
| Marek Cegielski Trans Ltd | Transport & logistics | 2021 |
| Marghritas 1 Limited | Hospitality | 2025 |
| Marghritas Limited | Hospitality | 2020 |
| Margot Design Ltd | Professional & scientific | 2026 |
| Margrie Services Limited | Other services | 2022 |
| Marian Transport Ltd | Transport & logistics | 2026 |
| Mariluc Ltd | Transport & logistics | 2021 |
| Marine Gauging International Ltd | Manufacturing | 2025 |
| Marinella Seafoods Limited | Wholesale & retail | 2007 |
| Mariner Foods Trading Limited | Wholesale & retail | 2013 |
| Mariner Groundworks Ltd | Other services | 2025 |
| Mariner Industries Ltd | Wholesale & retail | 2003 |
| Mariner Packaging Co Limited | Wholesale & retail | 2020 |
| Mariners Heating Plumbing GAS Limited | Construction | 2024 |
| Mariners Property Services Ltd | Real estate | 2025 |
| Mariop Trans Limited | Transport & logistics | 2019 |
| Maris Port Solutions Limited | Professional & scientific | 2012 |
| Mariusz Solution Ltd | Transport & logistics | 2019 |
| Marjara Care Group Limited | Financial services | 2020 |
| Marjara Management Services Limited | Administrative & support | 2023 |
| Mark Anglin Associates Limited | Real estate | 2000 |
| Mark Benedict Robinson Limited | Professional & scientific | 2012 |
| Mark Brook Installations Limited | Construction | 2016 |
| Mark Brown of Grimsby Ltd | Wholesale & retail | 2002 |
| Mark Camburn Driving School Limited | Education | 2002 |
| Mark Carlton Limited | Extraterritorial | 2012 |
| Mark Lucas Photography Limited | Professional & scientific | 2017 |
| Mark Pulford Financial Services Ltd | Financial services | 2012 |
| Mark S Davies and Co Limited | Professional & scientific | 2014 |
| Mark Stewart (Holdings) Limited | Financial services | 2025 |
| Mark Thomas Window Maintenance Limited | Construction | 2023 |
| Market Vendr Limited | Wholesale & retail | 2012 |
| Marketing SPACE4U Limited | Professional & scientific | 2019 |
| Marketside Tavern Ltd | Hospitality | 2023 |
| Markwind Limited | Professional & scientific | 2025 |
| Marmorearth Limited | Manufacturing | 2020 |