| Memfy Trading Ltd | Professional & scientific | 2017 |
| Menastar Limited | Information & communication | 1981 |
| Menmai Systems Ltd | Information & communication | 2025 |
| Mentana Properties Limited | Real estate | 2019 |
| Mercers Freehold Ltd | Extraterritorial | 2020 |
| Merchandise Branded Ltd | Professional & scientific | 2019 |
| Merchant Financial Services (UK) Ltd | Financial services | 2001 |
| Mercury Beech Ltd | Real estate | 2017 |
| Mercury Financials Limited | Professional & scientific | 2021 |
| Meredey Holdings Limited | Financial services | 2020 |
| Meridian Oncology Limited | Health & social care | 2026 |
| Merlin Analytics Limited | Information & communication | 2023 |
| Merlins Court (South Harrow) RTM Company Limited | Real estate | 2012 |
| Merrygood Ltd. | Wholesale & retail | 2007 |
| Mesfield Limited | Health & social care | 2022 |
| Mesogios Investments Limited | Administrative & support | 2003 |
| Meta App Ltd | Information & communication | 2022 |
| Metalin UK Limited | Administrative & support | 2002 |
| Metamerge UN Limited | Administrative & support | 2009 |
| Metcalfe Lancaster Limited | Professional & scientific | 2020 |
| Meticulous Solutions Limited | Information & communication | 2014 |
| Metonomy Ltd | Information & communication | 2020 |
| Metrics Management Limited | Administrative & support | 2012 |
| Metropoint Limited | Real estate | 2017 |
| Metropolitan Neurology Limited | Health & social care | 2023 |
| Meyers House Ltd | Real estate | 2024 |
| MEZ Construction (UK) Ltd | Construction | 2015 |
| MEZ Construction South Developments 2 Limited | Real estate | 2025 |
| MEZ Construction South Developments Ltd | Real estate | 2020 |
| MEZ Construction South Division Ltd | Construction | 2018 |
| MEZ Erections Ltd | Construction | 2026 |
| MEZ Waste Management Limited | Water & waste | 2020 |
| MFK Capital Limited | Real estate | 2024 |
| MFK Group Limited | Financial services | 2024 |
| MFR Online Ltd | Wholesale & retail | 2022 |
| MG Orthopaedics Ltd | Health & social care | 2015 |
| MGL VIP Chauffeurs Limited | Transport & logistics | 2015 |
| Mhfs Trading Limited | Professional & scientific | 2021 |
| MHS Transport Limited | Transport & logistics | 2021 |
| Michael Brady Commercial Limited | Construction | 2008 |
| Michael Brady Construction Limited | Construction | 2025 |
| Michael Brady London Limited | Construction | 2008 |
| Michael Brady Ltd. | Construction | 1992 |
| Michael Brady Residential Limited | Construction | 2025 |
| Michael Franklin(Chemists)Limited | Wholesale & retail | 1962 |
| Michael Goedhuis Limited | Wholesale & retail | 1980 |
| Michael Naik & Co Management Limited | Real estate | 1997 |
| Michael Naik and Co. Limited | Administrative & support | 1985 |
| Michael Quinn Contractors Limited | Construction | 2003 |
| Michaels Ross & Cole (U.K.) Limited | Information & communication | 1994 |
| Michele Hope by Design Limited | Financial services | 2019 |
| Micoach Limited | Education | 2019 |
| Micro Thermal Energy Limited | Professional & scientific | 2022 |
| Microdent Limited | Health & social care | 2011 |
| Midata Consulting Ltd | Information & communication | 2014 |
| Middlesex Radio Cars Ltd | Transport & logistics | 2026 |
| Mighty Cleaning & Maintenance Ltd | Administrative & support | 2015 |
| Mihaan Impex Ltd | Manufacturing | 2022 |
| Mike Marsland Photos Limited | Professional & scientific | 2012 |
| Miksbg Ltd | Other services | 2012 |
| Milenk Limited | Construction | 2007 |
| Miles Fuel Limited | Wholesale & retail | 2017 |
| Mili Solutions Limited | Information & communication | 2007 |
| Mill at Sonning (Theatre) Limited(The) | Hospitality | 1978 |
| Milton Care Limited | Health & social care | 2022 |
| Milverton Care Ltd | Health & social care | 2024 |
| Mim-Mithu Ltd | Other services | 2022 |
| Mims Trading Ltd | Wholesale & retail | 2021 |
| Mind Action Ltd | Education | 2009 |
| Mind Body Herbals Limited | Other services | 2017 |
| Mind the Lawn Limited | Wholesale & retail | 2024 |
| Mindful Consulting Ltd | Information & communication | 2017 |
| Mindruta Ltd | Construction | 2014 |
| Mindtree Technology Ltd | Information & communication | 2019 |
| Minerva Clinical Services Limited | Wholesale & retail | 2020 |
| Mini Cones Limited | Manufacturing | 2025 |
| Mint Craft Holdings Ltd | Financial services | 2025 |
| Mintlake Limited | Wholesale & retail | 2022 |
| Miny Ltd | Real estate | 2021 |
| Miram Capital Ltd | Professional & scientific | 2023 |
| Mirash 20 Ltd | Real estate | 2020 |
| Miraz Barbers Ltd | Other services | 2025 |
| Mirchris Ltd | Wholesale & retail | 2003 |
| Mirror Mirror Couture Limited | Manufacturing | 1989 |
| MIS Consultancy Services Ltd | Information & communication | 2003 |
| Mission Technologies Limited | Extraterritorial | 2003 |
| Mistry Sales & Marketing Ltd. | Wholesale & retail | 2019 |
| Miswell Operations Limited | Households | 2006 |
| Mita Samani Advisory Limited | Professional & scientific | 2023 |
| Mitahara Ltd | Hospitality | 2023 |
| Mitcham Healthcare Limited | Wholesale & retail | 2022 |
| Mitfair Limited | Wholesale & retail | 2016 |
| Mits Limited | Wholesale & retail | 2007 |
| Mitti and Mortar Ltd | Real estate | 2025 |
| Mitz Limited | Wholesale & retail | 2010 |
| MJ Capp Limited | Arts & recreation | 2013 |
| MJ Mobile Motor's Limited | Wholesale & retail | 2010 |
| MJ Product Solutions Limited | Professional & scientific | 2025 |
| MJ Rowlands Limited | Financial services | 2021 |
| MJB Platinum Ltd | Health & social care | 2016 |