| Mercedes-Benz Retail Group UK Limited | Wholesale & retail | 1946 |
| Mercedes-Benz UK Limited | Wholesale & retail | 1989 |
| Mercedes-Benz UK Share Trustee Limited | Professional & scientific | 2001 |
| Mercedes-Benz UK Trustees Limited | Financial services | 1982 |
| Mercedes-Benz Vans UK Limited | Wholesale & retail | 2016 |
| Merchant Mart Ltd | Wholesale & retail | 2021 |
| Merchants Place Bolton Limited | Real estate | 2020 |
| Merciless Media Limited | Information & communication | 2022 |
| Merco Healthcare Holdings Limited | Financial services | 2021 |
| Merco Medical Holdings Ltd | Financial services | 2011 |
| Merco Medical Staffing Limited | Administrative & support | 2002 |
| Mercol Group Limited | Financial services | 2020 |
| Mercurius IT Limited | Information & communication | 2005 |
| Mercury Estates (MK) Ltd | Real estate | 2016 |
| Mercury Estates LLP | | 2010 |
| Mercury Heat Solutions Limited | Construction | 2011 |
| Mercy Sparkle Services Limited | Administrative & support | 2024 |
| Meridian Projects Limited | Professional & scientific | 2026 |
| Meridianserv Ltd | Professional & scientific | 2018 |
| Meridies Consulting Ltd | Professional & scientific | 2015 |
| Merino Court Freehold Limited | Households | 2017 |
| Merinwell (Aberdeen) Limited | Real estate | 2025 |
| Merinwell (Dudley) Limited | Real estate | 2024 |
| Merinwell Limited | Construction | 1957 |
| Merinwell NO.1 Limited | Professional & scientific | 2024 |
| Merit Li-Lin UK Limited | Administrative & support | 1998 |
| Meritum Homecare Limited | Health & social care | 2020 |
| Merkur Bingo UK Limited | Professional & scientific | 1987 |
| Merkur Casino Entertainment UK Limited | Arts & recreation | 2023 |
| Merkur Casino Holdings UK Limited | Financial services | 2011 |
| Merkur Casino UK Ltd | Financial services | 2012 |
| Merkur Slots UK Limited | Arts & recreation | 1972 |
| Merkur Technical Support Limited | Professional & scientific | 2006 |
| Merlin Branding Ltd | Professional & scientific | 2021 |
| Merlin Cloud Consultancy Limited | Administrative & support | 2025 |
| Merrien Consultancy Ltd | Information & communication | 2023 |
| Merrifield Alpacas Limited | Agriculture & fishing | 2009 |
| Merritt Services Limited | Professional & scientific | 2004 |
| Mesabusa Limited | Hospitality | 2025 |
| Meshel Limited | Health & social care | 2023 |
| Meslec Ltd | Construction | 2015 |
| Meso Estetic Ltd | Health & social care | 2016 |
| Messagingmo Ltd | Manufacturing | 2010 |
| Messenger Newspapers Limited | Information & communication | 2019 |
| MET Commodities London Limited | Extraterritorial | 2013 |
| Meta Learn Limited | Professional & scientific | 2012 |
| Meta Storage Systems UK Limited | Construction | 2008 |
| Metabolic Health Clinic Ltd | Health & social care | 2024 |
| Metacoders AI Ltd | Information & communication | 2019 |
| Metadata Labs Ltd | Information & communication | 2022 |
| Metadata Matters Limited | Information & communication | 2006 |
| Metal Revive Limited | Manufacturing | 2025 |
| Metal Work Pneumatic UK Ltd | Wholesale & retail | 1985 |
| METALBOX77 Ltd | Wholesale & retail | 2022 |
| Metaltex (UK) Ltd. | Wholesale & retail | 1949 |
| Metalusa UK Limited | Manufacturing | 2012 |
| Metamorph Services Limited | Professional & scientific | 2024 |
| Metani Ltd | Professional & scientific | 2021 |
| Metatek-Group Ltd | Professional & scientific | 2022 |
| Method Tower Solutions Limited | Information & communication | 2023 |
| Method Wellbeing Limited | Health & social care | 2022 |
| Metrevive Ltd | Other services | 2023 |
| Metric Point Limited | Manufacturing | 2018 |
| Metrici Limited | Information & communication | 2005 |
| Metro Nest Limited | Real estate | 2024 |
| Metrocorp Investments Ltd | Real estate | 2017 |
| Metromerchandise Ltd | Wholesale & retail | 2021 |
| Metropole Search Partners Limited | Administrative & support | 2012 |
| Metropolitan Qualifications Ltd | Education | 2017 |
| Metropolitan-Cammell-Weymann Motor Bodies Ltd | Manufacturing | 2022 |
| Mettris Computeque Limited | Information & communication | 2018 |
| Meva Group Ltd | Professional & scientific | 2015 |
| MEW Style Ltd | Wholesale & retail | 2025 |
| MEZ Limited | Wholesale & retail | 2026 |
| Mezue Capital Ltd | Other services | 2016 |
| MFB Clothing and Sports Limited | Wholesale & retail | 2024 |
| MFE Consulting Solutions Limited | Information & communication | 2017 |
| Mfhouse Ltd | Real estate | 2024 |
| Mforte Limited | Hospitality | 2016 |
| MFS Reprographics Ltd | Administrative & support | 2009 |
| MG Audio & Visuals Limited | Information & communication | 2018 |
| MG Green Properties Ltd | Real estate | 2022 |
| MG Live-In Care Services Limited | Health & social care | 2024 |
| Mg&I Limited | Transport & logistics | 2021 |
| MGA Entertainment (UK) Limited | Wholesale & retail | 2005 |
| MGB Developments MK Ltd | Construction | 2021 |
| MGC Auto Works Ltd | Wholesale & retail | 2025 |
| MGK Services Ltd | Construction | 2015 |
| MGL Solution Limited | Administrative & support | 2025 |
| MGM (Guilden Morden) Limited | Construction | 2014 |
| MGM (HGP) Limited | Construction | 2019 |
| MGM (Hitchin) Limited | Construction | 2016 |
| MGM (Little Hadham) Limited | Construction | 2016 |
| MGM (Maulden) Limited | Construction | 2020 |
| MGM Holdings Limited | Financial services | 2016 |
| MGM Ickleford Limited | Construction | 2026 |
| Mgnana Limited | Health & social care | 2019 |
| Mgnh Associates Limited | Professional & scientific | 2023 |
| MGR 2016 Limited | Transport & logistics | 2016 |
| MGS IT Solutions Ltd | Information & communication | 2023 |