| Matfords Limited | Wholesale & retail | 2017 |
| Matic Technologies Limited | Information & communication | 2016 |
| Matrida Limited | Health & social care | 2015 |
| Matrix Architecture Ltd | Professional & scientific | 2012 |
| Matrix Health Services Holdings Ltd | Health & social care | 2014 |
| Matrix Health Services UK Limited | Health & social care | 2004 |
| Matros Digital Ltd | Professional & scientific | 2022 |
| Matt Auto Locksmith Ltd | Manufacturing | 2019 |
| Matt Burton Associates Ltd | Administrative & support | 2006 |
| Matt Frost Group Limited | Professional & scientific | 2023 |
| Mattco Gift Retailing Ltd | Manufacturing | 2019 |
| Matthan Consulting Ltd | Professional & scientific | 2026 |
| Matthew Charlton,Limited | Construction | 1939 |
| Matthew Cole Consulting Limited | Professional & scientific | 2019 |
| Matthew F Chambers Cyber Security Ltd | Professional & scientific | 2020 |
| Matthew H. Wilson & SON, Limited | Real estate | 1928 |
| Matthew Raine Ltd | Administrative & support | 2025 |
| Matthew Wood Developments Limited | Real estate | 1995 |
| Matthew Wood Fish and Chips Limited | Wholesale & retail | 2002 |
| Mattocks Solutions Ltd | Information & communication | 2025 |
| Mattress Shop Ltd | Administrative & support | 2005 |
| Mauda Property Ltd | Real estate | 2023 |
| Maudling Holdings Ltd | Professional & scientific | 2023 |
| Maureen Wood Tailoring Services Ltd | Other services | 2018 |
| Maus NE Limited | Health & social care | 2023 |
| Maverick Llama Limited | Education | 2025 |
| Mavid Limited | Public administration | 2023 |
| Mawadda International AID | Health & social care | 2011 |
| Mawiya Cleaning Services Ltd | Administrative & support | 2025 |
| Mawson Kerr Architects Ltd | Professional & scientific | 2010 |
| Mawson Kerr Trustees Limited | Administrative & support | 2022 |
| MAX Coen Ltd | Hospitality | 2025 |
| MAX Fixings Ltd | Wholesale & retail | 2010 |
| MAX Group One Limited | Wholesale & retail | 2017 |
| MAX Offshore Limited | Information & communication | 2014 |
| MAX Safe Company Ltd | Transport & logistics | 2016 |
| Maxecom Limited | Wholesale & retail | 2023 |
| Maxenden House Properties Ltd | Hospitality | 2003 |
| Maxflameuk Ltd | Wholesale & retail | 2020 |
| Maxi Consulting Ltd | Professional & scientific | 2026 |
| Maxideals Group Ltd | Wholesale & retail | 2019 |
| Maxim Property Solutions Ltd | Real estate | 2022 |
| Maxima Developments Limited | Hospitality | 2016 |
| Maximum-Smiles Ltd | Health & social care | 2025 |
| Maximus Care Limited | Professional & scientific | 2021 |
| Maxine Calvert Limited | Hospitality | 2002 |
| Maxing IT Enterprises Ltd | Wholesale & retail | 2025 |
| Maxman Financials Limited | Information & communication | 2024 |
| Maxman Properties Limited | Real estate | 2003 |
| Maxmary Ltd | Health & social care | 2023 |
| Maxmind Limited | Real estate | 2002 |
| Maxoli Electrical Services Limited | Construction | 2024 |
| Maxset Ltd | Health & social care | 2014 |
| Maxshop Ltd | Wholesale & retail | 2019 |
| MAY Craig Ltd | Real estate | 2023 |
| MAY Hong Washington Limited | Hospitality | 2016 |
| Maya Business Services Ltd | Professional & scientific | 2023 |
| Maya's Health Ltd | Public administration | 2021 |
| Mayacons Limited | Construction | 2026 |
| Mayajai Properties Limited | Real estate | 2018 |
| Mayborn (UK) Limited | Manufacturing | 1985 |
| Mayborn Group Limited | Professional & scientific | 1946 |
| Mayfield Studio Ltd | Professional & scientific | 2011 |
| Mayflower (Newcastle) Limited | Hospitality | 2005 |
| Maymask (121) Limited | Real estate | 2006 |
| Maymask (140) Limited | Real estate | 2009 |
| Maymask (158) Limited | Other services | 2010 |
| Maymask (170) Limited | Real estate | 2010 |
| Maymask (171) Limited | Information & communication | 2011 |
| Maymask (201) Limited | Extraterritorial | 2013 |
| Maymask (202) Limited | Hospitality | 2013 |
| Maymask (206) Limited | Hospitality | 2014 |
| Maymask (223) Limited | Financial services | 2017 |
| Maymask (226) Limited | Other services | 2017 |
| Maymask (228) Limited | Real estate | 2018 |
| Maymask (247) Limited | Health & social care | 2023 |
| Maymask (248) Limited | Health & social care | 2023 |
| Maymask (257) Limited | Health & social care | 2024 |
| Maymask (258) Limited | Financial services | 2025 |
| Maymask 209 Limited | Arts & recreation | 2012 |
| Maymask 3 Limited | Financial services | 2024 |
| Mayo Estate Ltd | Real estate | 2023 |
| Maysan Foods Limited | Manufacturing | 1963 |
| Maythorn Films Ltd | Information & communication | 2025 |
| Maytree Group Ltd | Real estate | 2001 |
| Maytree Housing Limited | Real estate | 2025 |
| Maytree Property Group Ltd | Real estate | 2023 |
| Mazi Architects Ltd | Professional & scientific | 2025 |
| Mazza Properties Ltd | Real estate | 2020 |
| Mazzini Ltd | Transport & logistics | 2015 |
| MB Biofollicle Consulting Ltd | Health & social care | 2026 |
| MB Investments Group Limited | Real estate | 2023 |
| MB Quesports Ltd | Arts & recreation | 2024 |
| MB2 Limited | Wholesale & retail | 2014 |
| MBA Temps Limited | Administrative & support | 2012 |
| MBC Draughting Ltd | Administrative & support | 2017 |
| MBC Recruitment Ltd | Administrative & support | 2023 |
| MBD Entertainment (NE) Limited | Hospitality | 2022 |
| Mbgp Limited | Construction | 2022 |
| MBH Motors Limited | Wholesale & retail | 2024 |