| Meal Plus Mart Ltd | Wholesale & retail | 2025 |
| Meanti Ltd | Construction | 2024 |
| Measure Design Limited | Administrative & support | 2009 |
| Measure Holdings Limited | Administrative & support | 2012 |
| Mecanica Engineering Ltd | Professional & scientific | 2016 |
| Mechanika Ltd | Construction | 2011 |
| MED Services Ltd | Administrative & support | 2023 |
| Medallion (Design and Development) Limited | Construction | 2020 |
| Medallion Real Estate Limited | Real estate | 2020 |
| Medan Consulting Ltd | Professional & scientific | 2026 |
| Medheart Consulting Ltd | Health & social care | 2025 |
| Medhurst Investments Ltd | Real estate | 2020 |
| Media Analytics Limited | Information & communication | 2002 |
| Media Management Ltd | Arts & recreation | 2024 |
| Mediation Support Limited | Agriculture & fishing | 2006 |
| Medical and Diagnostics Consultancy Ltd | Professional & scientific | 2024 |
| Medical Healthcare Staffing Ltd | Administrative & support | 2016 |
| Medical Marketing Holdings, LLC | | 2008 |
| Medical Product Consulting Ltd | Professional & scientific | 2016 |
| Medical Science Solutions Limited | Health & social care | 2000 |
| Medical Sciences Commercial Services Limited | Administrative & support | 2026 |
| Medicolegal-Opinion Ltd | Administrative & support | 2010 |
| Medicon Medical Services Limited | Health & social care | 2020 |
| Mediconnectuk Ltd | Information & communication | 2018 |
| Medina Supermarket Oxford Ltd | Wholesale & retail | 2025 |
| Medinah Supermarket Oxford Ltd | Wholesale & retail | 2025 |
| Medistress Ltd | Health & social care | 2013 |
| Medisyne Ltd | Manufacturing | 2016 |
| Medlearn Ltd | Wholesale & retail | 2020 |
| Medward Trading Ltd | Administrative & support | 2025 |
| Meenahs Health Care Ltd | Administrative & support | 2023 |
| Megamind Investments Ltd | Financial services | 2026 |
| Meiwei Oxford Limited | Hospitality | 2025 |
| Melente Ltd | Construction | 2023 |
| Melgan Burt Ltd | Administrative & support | 2012 |
| Melham Services Limited | Professional & scientific | 2025 |
| Melio BIO Limited | Professional & scientific | 2024 |
| Meliometrics Ltd | Information & communication | 2020 |
| Melior Medical Ltd | Health & social care | 2016 |
| Melissa Barkan Consulting Ltd | Health & social care | 2023 |
| Mellowood Properties Limited | Real estate | 1997 |
| Mellt Holdings Ltd | Financial services | 2025 |
| Melton Mowbray Ltd | Public administration | 2023 |
| Melu Limited | Information & communication | 2018 |
| Member Corp Ltd | Wholesale & retail | 2021 |
| Mendes Services Ltd | Administrative & support | 2019 |
| Mennta Energy Solutions (Holdings) Limited | Professional & scientific | 1998 |
| Mennta Energy Solutions Limited | Education | 1982 |
| Menon Advisory Limited | Professional & scientific | 2017 |
| Mentaco Ltd | Health & social care | 2020 |
| Mentors International Limited | Education | 2025 |
| Meow Meow Books Ltd | Information & communication | 2025 |
| Meow Meow Farm Ltd | Agriculture & fishing | 2025 |
| Merakistore Limited | Wholesale & retail | 2018 |
| Mercedes Stockton Limited | Financial services | 2023 |
| Mercer 79 Ltd | Manufacturing | 2026 |
| Mercer Lewin Ltd | Professional & scientific | 2014 |
| Merchants Place Residents Management Company Limited | Households | 2004 |
| Mercurio International Limited | Professional & scientific | 2014 |
| Mercyme Ltd | Health & social care | 2016 |
| Meredene Holdings Limited | Real estate | 2025 |
| Meredene Limited | Real estate | 2002 |
| Merewood Freehold Limited | Households | 2013 |
| Merewood Healthcare Services Limited | Health & social care | 2015 |
| Meriden (Boars Hill) Management Limited | Real estate | 2002 |
| Meridian Capital Investments Limited | Wholesale & retail | 2011 |
| Meridian Global Ventures Ltd | Hospitality | 2024 |
| Meridian Quay Management Company Limited | Real estate | 2006 |
| Meridian Smile Ltd | Health & social care | 2025 |
| Merindol Consulting Ltd | Professional & scientific | 2012 |
| Merit Brand Holdings Ltd | Professional & scientific | 2023 |
| Mermaid Gloucester Ltd | Hospitality | 2015 |
| Merrycroft Limited | Professional & scientific | 1989 |
| Merryfield Home Limited | Health & social care | 1988 |
| Merton College NO. 1 Limited | Real estate | 2020 |
| Merton Enterprises Limited | Real estate | 2000 |
| Metapop Star Ltd | Information & communication | 2023 |
| Metavisionaries.Incglobal Limited | Education | 2023 |
| Metavisionaryincglobal Limited | Education | 2025 |
| Methree Limited | Information & communication | 2023 |
| Metlase Limited | Manufacturing | 2015 |
| Metrichor Limited | Extraterritorial | 2013 |
| Metriqauk Ltd | Construction | 2020 |
| Metrogold Consultants Ltd | Other services | 2010 |
| Metrostationery Solutions Ltd | Manufacturing | 2025 |
| Metsims Limited | Professional & scientific | 2018 |
| Mettis Projects Limited | Extraterritorial | 2024 |
| Mewotec (UK) Limited | Wholesale & retail | 1992 |
| Mewstone Capital Ltd | Financial services | 2023 |
| Meydan Asset Management Limited | Professional & scientific | 2013 |
| Meyer Leboeuf Limited | Information & communication | 2013 |
| Mezbaan Property Management Limited | Real estate | 2025 |
| Mf-Electrical Oxford Ltd | Construction | 2022 |
| MFR Plastering Ltd | Construction | 2025 |
| MFZ Medical Services Limited | Professional & scientific | 2010 |
| MG Property Maintenance & Services Ltd | Construction | 2015 |
| MGP Ventures Ltd | Transport & logistics | 2026 |
| Mgqs Services Limited | Professional & scientific | 2020 |
| MGX Enterprises Limited | Financial services | 2025 |
| Mheaven Ltd | Construction | 2022 |