| Mark Davies Limited | Administrative & support | 2003 |
| Mark Hill Auctions Limited | Wholesale & retail | 2024 |
| Mark Richard Jones Limited | Extraterritorial | 2025 |
| Mark Watson Surgical Services Ltd | Health & social care | 2019 |
| Markerstudy (Affinity) Holdings Limited | Financial services | 2018 |
| Markerstudy Direct Limited | Financial services | 1996 |
| Markerstudy Group Holdings Limited | Administrative & support | 2020 |
| Markerstudy Group Investments Limited | Financial services | 2021 |
| Markerstudy Group Limited | Administrative & support | 2020 |
| Markerstudy Group Services Limited | Financial services | 2023 |
| Markerstudy Group Treasury Limited | Financial services | 2019 |
| Markerstudy Holdings (UK) Limited | Extraterritorial | 2013 |
| Markerstudy Insurance Services Limited | Financial services | 1987 |
| Markerstudy Limited | Financial services | 2018 |
| Markerstudy Property Holdings (NO.1) Limited | Financial services | 2021 |
| Markerstudy Property Holdings Limited | Financial services | 2021 |
| Market My Product Ltd | Professional & scientific | 2015 |
| Marlin Chemicals Limited | Financial services | 1982 |
| Marlin Productions Limited | Arts & recreation | 2021 |
| Marling Building Services Limited | Construction | 2009 |
| Marrow Healthcare Ltd | Professional & scientific | 2026 |
| Marsegu Ltd | Information & communication | 2023 |
| Martial Therapist Ltd | Other services | 2021 |
| Martins Developments Ltd | Construction | 2015 |
| Martyn-David Associates Limited | Professional & scientific | 2009 |
| Marvanova Ltd | Information & communication | 2026 |
| Mason Brennan Gleeson French Ltd | Professional & scientific | 2022 |
| Mason International Consulting Ltd | Professional & scientific | 2015 |
| Masters of Beckenham (2003) Limited | Extraterritorial | 1992 |
| Masters of Beckenham Limited | Wholesale & retail | 1952 |
| Masterwood GB Holdings Ltd | Financial services | 2018 |
| Mastrick Productions Limited | Information & communication | 2021 |
| Matchbox Motors Limited | Wholesale & retail | 2025 |
| Materia Limited | Financial services | 2013 |
| Mathlete.Io Ltd | Information & communication | 2024 |
| Maths Mastery Academy Ltd | Education | 2020 |
| Matrix Apparel Ltd | Wholesale & retail | 2024 |
| Matthew Cross Hair Limited | Other services | 2010 |
| Matthew Hill Coach Trimming Limited | Wholesale & retail | 2018 |
| Maule Properties Limited | Real estate | 2019 |
| Mauluka Limited | Wholesale & retail | 2018 |
| MAV Reality Limited | Wholesale & retail | 2021 |
| Mavericks IP Ltd | Professional & scientific | 2018 |
| Mawson Capital Limited | Extraterritorial | 2010 |
| MAX William Music Ltd | Information & communication | 2018 |
| Maxam Digital Ltd | Information & communication | 2024 |
| Maxatta Limited | Information & communication | 2017 |
| Maxguard Roofing Solutions Ltd | Construction | 2024 |
| Maxime Consulting Ltd | Administrative & support | 2019 |
| Maxxi Childcare Limited | Education | 2022 |
| Maxxi Holdings Limited | Financial services | 2022 |
| Maxxi Nurseries Limited | Education | 2022 |
| MAY Harris Limited | Extraterritorial | 2015 |
| MAY Harris Multi Services Ltd | Administrative & support | 2009 |
| Mayfair Global Management Limited | Professional & scientific | 2018 |
| Mayflower Transport Consultancy Ltd | Professional & scientific | 2025 |
| Maygreen Limited | Wholesale & retail | 2016 |
| Maylr DPO Ltd | Transport & logistics | 2021 |
| Maylr Ltd | Manufacturing | 2020 |
| Maysi Foods Ltd | Wholesale & retail | 2022 |
| Mazet Properties Ltd | Real estate | 2026 |
| MBI Healthcare Limited | Health & social care | 2011 |
| Mbip Ltd | Real estate | 1995 |
| MBM Investment Group Limited | Households | 2022 |
| Mbody Elite Ltd | Arts & recreation | 2023 |
| MBW (Apartment 9) Limited | Real estate | 2026 |
| MBW (IOW) Management Ltd | Households | 2026 |
| Mbxpress Transport Ltd | Transport & logistics | 2024 |
| MC Investments Holding Limited | Financial services | 2023 |
| MC Trading Limited | Wholesale & retail | 2008 |
| MCA Registrars Limited | Administrative & support | 1999 |
| Mcadam Family Limited | Real estate | 2022 |
| Mcai Consulting Ltd | Information & communication | 2020 |
| MCB Projects Ltd | Real estate | 2021 |
| MCC Property Consulting Services Ltd | Real estate | 2010 |
| Mccormick Editorial Services Limited | Information & communication | 2018 |
| Mccormick Group Ltd | Extraterritorial | 2023 |
| Mcdonnell Plastering & Decorating Limited | Construction | 2008 |
| Mcguire Consultancy Limited | Professional & scientific | 2010 |
| MCH Futures Ltd | Information & communication | 2026 |
| Mclachlan Developments Ltd | Real estate | 2022 |
| Mclay EHS Limited | Professional & scientific | 2012 |
| Mcmonagle Rock Limited | Wholesale & retail | 2026 |
| MCR Estates Limited | Financial services | 2013 |
| MCR Media Limited | Information & communication | 2001 |
| Mcritchie Group Limited | Financial services | 2024 |
| MD Advertising & Print Ltd | Manufacturing | 2023 |
| MD Agencies Ltd | Administrative & support | 2014 |
| MD and MZ Limited | Real estate | 2014 |
| MDA South East Limited | Wholesale & retail | 2022 |
| Mdam Services Ltd | Wholesale & retail | 2022 |
| Mdntech Ltd | Manufacturing | 2016 |
| MDS Scaffolding Services Ltd | Construction | 2024 |
| Me&You Creative Limited | Professional & scientific | 2010 |
| Meade Court Edenbridge Management Company Limited | Households | 2012 |
| Meadow Financial Holdings Limited | Professional & scientific | 2024 |
| Meadow Gate (Properties) Limited | Construction | 2000 |
| Meadow House Consulting Limited | Financial services | 2019 |
| Meadow International Ltd | Wholesale & retail | 2025 |
| Meadowstag Properties Limited | Real estate | 1974 |