| MAG Safety Solutions Limited | Administrative & support | 2017 |
| Magical UK Limited | Education | 2008 |
| Magnetic Memories Ltd | Professional & scientific | 2025 |
| Magnum Entertainment Ltd | Arts & recreation | 2023 |
| Maharaja N Limited | Hospitality | 2026 |
| Maharlika Foods Import and Export Ltd | Wholesale & retail | 2021 |
| Mahfooz Logistics Ltd | Transport & logistics | 2025 |
| Mahoney Audio Post Ltd | Information & communication | 2012 |
| Maidmamma Ltd | Professional & scientific | 2026 |
| Main-Tel (NE) Limited | Information & communication | 2000 |
| Mains Energy Solutions Ltd | Construction | 2025 |
| Mainside Limited | Households | 2019 |
| MAK Testing Ltd | Professional & scientific | 2018 |
| Makeaspect Limited | Hospitality | 1997 |
| Making Safety Simple Ltd | Professional & scientific | 2023 |
| Makoautos Ltd | Wholesale & retail | 2025 |
| MAL Gleeson Services Limited | Real estate | 2011 |
| MAL Interiors Ltd | Manufacturing | 2024 |
| Mamamda Limited | Hospitality | 2023 |
| Mamma Social Co Limited | Information & communication | 2022 |
| Mammoth Construction Services Ltd | Construction | 2025 |
| Mamoyo's Kitchenette Ltd | Hospitality | 2025 |
| MAN & Food Ltd | Hospitality | 2025 |
| Managed Work Space Solutions Ltd | Wholesale & retail | 2019 |
| Mandale Couriers Ltd | Transport & logistics | 2017 |
| Mandeville Properties Ltd | Real estate | 2020 |
| Mane Mission CIC | Other services | 2023 |
| Mango INT Limited | Transport & logistics | 2012 |
| Mann Haulage Limited | Transport & logistics | 2004 |
| Manor House (1707) Group Limited | Financial services | 2018 |
| Manor House (1707) Ltd | Real estate | 2014 |
| Manordrive Strategic Investments Limited | Financial services | 2021 |
| Manosose Limited | Professional & scientific | 2025 |
| Mansukh & Sons Ltd | Real estate | 2025 |
| Mantle Engineering Services Ltd | Construction | 2023 |
| Manus Neurodynamica Ltd | Professional & scientific | 2008 |
| Manxguard Limited | Professional & scientific | 1980 |
| MAP Building Solutions Limited | Extraterritorial | 2002 |
| MAP Energy Ltd | Construction | 2011 |
| MAP Group (UK) Limited | Construction | 1993 |
| MAP Group Ltd | Construction | 2023 |
| MAP Network Solutions Limited | Extraterritorial | 2008 |
| Maple Oak Homes Limited | Construction | 2017 |
| Maple Oak Living Limited | Real estate | 2020 |
| Mapleleaf Property Developments Limited | Real estate | 2003 |
| MAQ1 Limited | Wholesale & retail | 2017 |
| Marathon Rentals Limited | Real estate | 2023 |
| Marblemand Limited | Real estate | 1978 |
| Marc Jemmeson Access & Construction Limited | Construction | 2014 |
| Mardankat Ltd | Construction | 2019 |
| Mariserve Limited | Other services | 2011 |
| Mark Bravey E&I Services Limited | Construction | 2024 |
| Mark Ferens Qa/Qc Inspection Services Limited | Professional & scientific | 2010 |
| Mark Jordinson Limited | Health & social care | 2011 |
| Mark Riley Management Services Ltd | Construction | 2022 |
| Mark Steel Property Solutions Limited | Real estate | 2016 |
| Mark William Cowen Ltd | Construction | 2011 |
| Market Tavern Thornaby Ltd | Hospitality | 2024 |
| Marketing Skills Academy Ltd | Professional & scientific | 2018 |
| Markitme Ltd | Wholesale & retail | 2026 |
| Marley Aesthetics Ltd | Health & social care | 2023 |
| Marley Holdings Ltd | Wholesale & retail | 2023 |
| Marley Travel Services Ltd | Administrative & support | 2023 |
| Marlin Corporate Finance Limited | Financial services | 2017 |
| Marlin Group Limited | Professional & scientific | 2017 |
| Marlin Mortgages Limited | Financial services | 2024 |
| Marquis OIL and GAS Services Limited | Professional & scientific | 2025 |
| Mars Distribution Limited | Administrative & support | 2017 |
| Marseille Associates Limited | Administrative & support | 2016 |
| Marsh Howe Limited | Real estate | 2013 |
| Marshall Clean Heat and Power Ltd | Construction | 2008 |
| Marshall Green Engineering Limited | Manufacturing | 2015 |
| Marshall's Cladding & Roofing Limited | Construction | 2002 |
| Martin FOX Style Limited | Other services | 2016 |
| Martin Gibb Associates Limited | Professional & scientific | 2016 |
| Martin Grant Transport Ltd | Transport & logistics | 2009 |
| Martin Greenidge Building and Civils Ltd | Construction | 2021 |
| Martindale Transport Limited | Transport & logistics | 2019 |
| Marton Electrical Limited | Construction | 1999 |
| Marton Manor News Ltd | Wholesale & retail | 2018 |
| Marty Mcfry's Holding Company Limited | Hospitality | 2020 |
| Marty Mcfry's Limited | Hospitality | 2017 |
| Marvel Energy Ltd | Energy | 2023 |
| Maryam 369 Ltd | Wholesale & retail | 2022 |
| MAS GAS Ltd | Construction | 2026 |
| MAS Lifting Ltd | Professional & scientific | 2026 |
| MAS Ventilation Solutions Ltd | Construction | 2021 |
| MAS Welding Machine Repairs Ltd | Manufacturing | 2018 |
| Masada Developments Limited | Real estate | 2000 |
| Masons PDC Limited | Construction | 2018 |
| Master Grafix Ltd | Manufacturing | 2020 |
| Master Learning Ltd | Education | 2024 |
| Masterminds EAM Consulting Ltd | Information & communication | 2025 |
| MAT Accountancy Services Ltd | Professional & scientific | 2009 |
| MAT Property Investments Ltd | Real estate | 2020 |
| Mate Motors Limited | Wholesale & retail | 2021 |
| Matrix(North East) Ltd | Real estate | 2023 |
| Matthew Lagan Property Solutions Limited | Real estate | 2022 |
| Matthew Smith Maritime Solutions Ltd | Manufacturing | 2019 |
| Matthews Estate Investments Ltd | Real estate | 2026 |