| Mercer Conway Ltd | Professional & scientific | 2022 |
| Mercury Auto Refinishers Limited | Wholesale & retail | 2013 |
| Meredith Beauty Limited | Other services | 2025 |
| Meredith Clinic Ltd | Other services | 2022 |
| Meredith Medical Limited | Other services | 2016 |
| Meredith Training Ltd | Education | 2022 |
| Meridian BA Solutions Limited | Information & communication | 2010 |
| Meridian Kung FU LLP | | 2013 |
| Merk Construction Limited | Construction | 2024 |
| Merk Scaffolding Limited | Other services | 2010 |
| Merk Transport Services Ltd | Transport & logistics | 2016 |
| Merlindoc Limited | Administrative & support | 2024 |
| Merlinscan Ltd | Information & communication | 2025 |
| Merrett Solutions Ltd | Extraterritorial | 2017 |
| Merry by Name Ltd | Information & communication | 2011 |
| Merrygold Properties Limited | Real estate | 2025 |
| Merseyside Property Centre Ltd | Real estate | 2017 |
| Messkit Ltd | Manufacturing | 2005 |
| MET Concrete Supplies Ltd | Manufacturing | 2019 |
| MET Developments Ltd | Construction | 2013 |
| MET Logistics Ltd | Transport & logistics | 2021 |
| MET Resources LLP | | 2010 |
| Meta Consultancy Services Ltd | Information & communication | 2022 |
| Metal Coat Ltd | Manufacturing | 2020 |
| Metalmin & Co UK Limited | Wholesale & retail | 1974 |
| Metfab Essex Limited | Other services | 2010 |
| Mets (Covent Garden) Ltd | Construction | 2018 |
| Mews Trading Limited | Hospitality | 2013 |
| Meyer Properties Ltd | Real estate | 2013 |
| MF Holding Group Ltd | Real estate | 2024 |
| MFM Ventures Ltd | Financial services | 2026 |
| MFO MLG Properties Limited | Real estate | 2021 |
| MG SURVEY3D Ltd | Professional & scientific | 2019 |
| MGH Construction Ltd | Construction | 2007 |
| MGH Property Holdings Limited | Real estate | 2024 |
| MH Bedding Store Ltd | Wholesale & retail | 2021 |
| MH Health Benefits Limited | Professional & scientific | 2016 |
| Mhfed International Ltd | Extraterritorial | 2015 |
| MHM (M&E) Services Ltd | Professional & scientific | 2018 |
| MHM Abode Ltd | Real estate | 2025 |
| MHM Consulting (London) Limited | Professional & scientific | 2020 |
| MHT Investments Limited | Real estate | 2018 |
| MI Contracting Ltd. | Construction | 2015 |
| MIC Lawrence Limited | Construction | 2009 |
| Michael Brown Associates Limited | Professional & scientific | 1991 |
| Michael Cruise Coach Ltd | Other services | 2026 |
| Michael Linehan Property Services Limited | Extraterritorial | 2015 |
| Michael Rose Holdings Limited | Real estate | 2024 |
| Michelle James Properties Limited | Real estate | 2025 |
| Midrand Care Limited | Health & social care | 2013 |
| Midway Agency Ltd | Professional & scientific | 2024 |
| Mighty Agency Limited | Other services | 2001 |
| Mike Carpentry Limited | Construction | 2017 |
| Mike's Sports Therapy Limited | Arts & recreation | 2022 |
| Mikk Ltd | Financial services | 2019 |
| Mikuyu Tanzania | Administrative & support | 2007 |
| Milan & AVA Ltd | Hospitality | 2023 |
| Mildbury Limited | Information & communication | 2023 |
| Mildmay Park Management Company Limited | Households | 1996 |
| Mill View Residents Management Limited | Households | 2022 |
| Miller Leisure Limited | Arts & recreation | 2000 |
| Miller Restaurants Limited | Hospitality | 2012 |
| Millhead Limited | Professional & scientific | 2015 |
| Milli Cabs Ltd | Transport & logistics | 2026 |
| Millie Developments Limited | Construction | 2025 |
| Milner Property Developments Limited | Real estate | 2023 |
| Milo Fitness Limited | Arts & recreation | 2020 |
| Milton House (Westcliff) Ltd | Professional & scientific | 2020 |
| Minals Properties Ltd | Real estate | 2026 |
| Mindful Wealth Limited | Financial services | 2019 |
| Mindopsgroup Limited | Professional & scientific | 2025 |
| Mindsherpa Publishing House Ltd | Wholesale & retail | 2024 |
| Ming Property Solutions Ltd | Real estate | 2011 |
| Mini & ME Soft Play Limited | Arts & recreation | 2026 |
| Mini and ME Play Café Limited | Hospitality | 2025 |
| Mini Champs Ltd | Education | 2023 |
| Miricha Ltd | Real estate | 2023 |
| Mirror Scents Ltd | Wholesale & retail | 2025 |
| Miss Milburn's Tuition Ltd | Education | 2025 |
| Mitchell-Rose Ltd | Construction | 2021 |
| Mitty Property Holdings Limited | Real estate | 2022 |
| MJB Metal Group Ltd | Manufacturing | 2004 |
| Mjcm Limited | Financial services | 2019 |
| MJH Advisory Limited | Professional & scientific | 2025 |
| MJH Associates Ltd | Professional & scientific | 2026 |
| Mjordan Homes Limited | Construction | 2010 |
| MJW Services (Essex) Ltd | Construction | 2025 |
| MK Plant Hire Ltd | Water & waste | 2018 |
| MKF Andy Dennis Ltd | Arts & recreation | 2022 |
| MLA Building Services Limited | Construction | 2009 |
| MM Electrical Ltd | Construction | 2005 |
| MM Elite Ltd | Real estate | 2026 |
| Mmanigou Ltd | Real estate | 2026 |
| Mmch Properties Ltd | Real estate | 2024 |
| Mmps Salons Limited | Administrative & support | 2015 |
| MO H Solar Installations Ltd | Construction | 2025 |
| MO Leigh Enterprises Ltd | Hospitality | 2025 |
| MOB Installations Ltd | Construction | 2007 |
| Mobius Advisory Group Ltd | Professional & scientific | 2021 |
| Mobius Buildings Ltd | Real estate | 2026 |