| Mammoth Finance Limited | Financial services | 2015 |
| Mammoth Holdings Limited | Financial services | 2023 |
| Mammoth Retail Limited | Administrative & support | 2022 |
| Mammoth SPV Limited | Financial services | 2026 |
| Mamoyo Care Limited | Health & social care | 2014 |
| Mams Kitchen NE Ltd | Hospitality | 2024 |
| Mamun Ahmed Ltd | Financial services | 2019 |
| Management & Investment Limited | Professional & scientific | 1997 |
| Management Services (NE) Limited | Other services | 2021 |
| Manasik Travels Ltd | Administrative & support | 2015 |
| Manchester Residences (New Cross) Limited | Construction | 2018 |
| Manchester Spinal Services Ltd | Health & social care | 2015 |
| Mandale Commercial Limited | Wholesale & retail | 2001 |
| Mandata (Holdings) Limited | Information & communication | 2013 |
| Mandata (Management and Data Services) Ltd | Information & communication | 1997 |
| Mandata Group Limited | Financial services | 2018 |
| Mandata Network Limited | Information & communication | 2020 |
| Mandata Solutions Limited | Information & communication | 2020 |
| Mandell Place (Embleton) Management Company Limited | Households | 2019 |
| Mandeya Ltd | Professional & scientific | 2025 |
| Mandorley Ltd | Information & communication | 2026 |
| Mandy Construction 07 Ltd | Construction | 2022 |
| Mane Tamer Ltd | Wholesale & retail | 2024 |
| Manga Brews Ltd | Manufacturing | 2025 |
| Manga Estates Ltd | Real estate | 2022 |
| Manga Stores Ltd | Wholesale & retail | 2008 |
| Mangalci Limited | Hospitality | 2017 |
| Mango Studio Productions Ltd | Information & communication | 2009 |
| Mangrove (NE) Ltd | Construction | 2013 |
| Manh LE Supermarket Ltd | Wholesale & retail | 2024 |
| Manhattan Grill House Ltd | Other services | 2019 |
| Manhattan Pizza Sunderland Ltd | Hospitality | 2019 |
| Manhua CHA Ltd | Hospitality | 2016 |
| Manhua CHA Retail Limited | Wholesale & retail | 2023 |
| Manila Casual Dining Ltd | Hospitality | 2019 |
| Manioca Ltd | Financial services | 2014 |
| Manissa Ltd | Wholesale & retail | 2005 |
| Manitowoc Holdings (UK) Limited | Financial services | 1937 |
| Mankind Group Ltd | Real estate | 2026 |
| Manley & Mullin Ltd | Real estate | 2023 |
| Mann Singh Limited | Other services | 2003 |
| Manners (Newcastle) Limited | Hospitality | 2007 |
| Manor Court (Solihull) Management Limited | Households | 2005 |
| Manor Park Holiday Park Limited | Hospitality | 2006 |
| Manorville (Simla) Limited | Hospitality | 2015 |
| Manrekh Ltd | Real estate | 2026 |
| Mansha-Tech Limited | Wholesale & retail | 2014 |
| Manson Property Consultants Limited | Real estate | 2001 |
| Mantara Health Ltd | Health & social care | 2020 |
| Mantle Digital Ltd | Information & communication | 2011 |
| Mantra Thai Limited | Hospitality | 2009 |
| Manual Services Limited | Professional & scientific | 2014 |
| Manufacturing Automation Resources Limited | Administrative & support | 2017 |
| Manydown 2007 Limited | Financial services | 2007 |
| Manydown 2018 Limited | Financial services | 2018 |
| Manydown Holdings Limited | Financial services | 2018 |
| Maple Environmental Limited | Professional & scientific | 2024 |
| Maple Terrace Masonic Temple Limited | Other services | 1957 |
| Maple Tree MED CAN Consultancy Ltd | Health & social care | 2019 |
| Maps Technology Limited | Manufacturing | 2007 |
| Marach Property Limited | Real estate | 2021 |
| Maracheril Properties Ltd | Real estate | 2024 |
| Marachyz Ltd | Manufacturing | 2025 |
| Maradona Ltd | Hospitality | 2020 |
| Maratha Ltd | Hospitality | 2023 |
| Marcantonio Property Ltd | Construction | 2023 |
| March 2000 Limited | Administrative & support | 1997 |
| Marchwood Motorways (Southampton) Limited | Professional & scientific | 1982 |
| Marcommed CIC | Other services | 2024 |
| Marconi House RTM Company Limited | Real estate | 2012 |
| Marcore Limited | Mining & quarrying | 2022 |
| Marcus Global Foods Ltd | Wholesale & retail | 2025 |
| Marden Bridge Sports Hub Ltd | Arts & recreation | 2024 |
| Maresi Ltd | Professional & scientific | 2026 |
| Marfk Ltd | Construction | 2026 |
| Margaret Katherine Ltd | Construction | 2016 |
| Margarita Hope Photography Ltd | Professional & scientific | 2022 |
| Margrave Estates Limited | Real estate | 1937 |
| Mari Newcastle Ltd | Construction | 2026 |
| Marie Clark Psychotherapy & Yoga Ltd | Health & social care | 2022 |
| Mariellie’S Ltd | Hospitality | 2023 |
| Marilaps Ltd | Wholesale & retail | 2025 |
| Marin Design Investment Ltd | Real estate | 2025 |
| Marina Hotels Limited | Hospitality | 2005 |
| Marine & Offshore (Scotland) Limited | Construction | 1986 |
| Marine and Offshore Engineering Consultancy and Technical Sales Limited | Manufacturing | 2016 |
| Marine Law Solicitors Limited | Professional & scientific | 2009 |
| Marine Matrix Ltd | Wholesale & retail | 2024 |
| Mariners Rest Amble Ltd | Construction | 2020 |
| Mariners Way (Seaham) Management Company Limited | Real estate | 2012 |
| Marinovski Ltd | Professional & scientific | 2020 |
| Mario Handy MAN Ltd | Construction | 2022 |
| MARIO7 Cleaning Ltd | Administrative & support | 2019 |
| Marisam Events Ltd | Arts & recreation | 2023 |
| Marjacsar Limited | Professional & scientific | 2006 |
| Mark Beasy Limited | Information & communication | 2018 |
| Mark Butcher Associates Ltd | Professional & scientific | 2002 |
| Mark Construction & Design Ltd | Construction | 2022 |
| Mark Gordon (DR of Chiropractic) Limited | Health & social care | 2010 |
| Mark Harding Animal Physiotherapy Ltd | Professional & scientific | 2015 |