| Maverazula Ltd | Wholesale & retail | 2025 |
| MAX DAN Engineering Ltd | Professional & scientific | 2013 |
| MAX Fellows Consultancy Ltd | Professional & scientific | 2021 |
| Max-Electrical Surrey Ltd | Construction | 2018 |
| Maximai.Cx Ltd | Information & communication | 2025 |
| Maximus Life Limited | Wholesale & retail | 2014 |
| Maxinn Holdings Limited | Construction | 2016 |
| Maxwheel Motors Limited | Wholesale & retail | 2017 |
| Maxy Epsom Ltd | Wholesale & retail | 2023 |
| MAY Mortgages Ltd | Financial services | 2021 |
| Maya Blue Limited | Professional & scientific | 2010 |
| Mayander Ltd | Real estate | 2025 |
| Maybridge Consultancy Limited | Real estate | 2012 |
| Mayer Building Developments Limited | Construction | 2024 |
| Mayfair Property and Estates LLP | | 2009 |
| Mayfair Trading London Ltd | Information & communication | 2025 |
| Mayfield International Ltd | Professional & scientific | 2010 |
| Mayfield Lavender Limited | Agriculture & fishing | 2006 |
| Mayfields Property Management Limited | Households | 1993 |
| Mayfly Kiwi Estates Ltd | Real estate | 2025 |
| Maysante Consultancy Ltd | Professional & scientific | 2016 |
| Mazen Ghannoum Ltd | Professional & scientific | 2026 |
| Mazm Services Limited | Transport & logistics | 2019 |
| Mazyl & Ibrahim Ltd | Hospitality | 2022 |
| MB Advisory Limited | Administrative & support | 2020 |
| MB Outfitters Ltd | Hospitality | 2026 |
| MBL (Holding) Ltd | Financial services | 2022 |
| MBS Property Holdings Ltd | Real estate | 2026 |
| MBW Limited | Other services | 2025 |
| Mbzjt Ltd | Transport & logistics | 2023 |
| MC Change Consulting Limited | Professional & scientific | 2015 |
| Mccaffreys Limited | Other services | 2008 |
| Mccarter Consulting Limited | Information & communication | 2018 |
| Mcdermott SF Consulting Limited | Administrative & support | 2013 |
| MCG Tradex Ltd | Wholesale & retail | 2024 |
| Mcgarry Blinds Limited | Manufacturing | 2009 |
| Mcgee Ductwork Limited | Manufacturing | 2010 |
| MCH Professional Services Limited | Professional & scientific | 2012 |
| Mcilwham Music Ltd | Professional & scientific | 2008 |
| Mckenna Properties UK Limited | Construction | 1996 |
| MCM Procurement Ltd | Professional & scientific | 2009 |
| MCW Global Consulting Ltd | Professional & scientific | 2023 |
| MDB Rail Ltd | Transport & logistics | 2025 |
| Mdbargainhub Limited | Wholesale & retail | 2024 |
| MDK13 Ltd | Wholesale & retail | 2022 |
| ME Group International PLC | Other services | 1962 |
| Meadow Court (East) Residents Co. (Walton) Limited | Real estate | 1993 |
| Meadow Court (Walton) Residents Co. Limited | Real estate | 1993 |
| Meadow Court (West) Residents Co. (Walton) Limited | Real estate | 1993 |
| Meadow Gate Solutions Ltd | Professional & scientific | 2024 |
| Meadowbridge Court RTM Company Limited | Real estate | 2010 |
| Meads Tido Limited | Wholesale & retail | 2018 |
| Mecatherm UK Ltd | Professional & scientific | 2025 |
| Mechials Holding Limited | Financial services | 2024 |
| MED - LEC Electrical Contractors Ltd | Construction | 2008 |
| MED Sync Solutions Limited | Administrative & support | 2025 |
| Med-Lec Group Holdings Ltd | Financial services | 2021 |
| Medally Ltd | Health & social care | 2024 |
| Medi Labs Ltd | Health & social care | 2024 |
| Media Boxx Ltd | Professional & scientific | 2021 |
| Media Hire Solutions Limited | Construction | 2025 |
| Medical AI Limited | Information & communication | 2023 |
| Meditation Mountain Ltd | Information & communication | 2023 |
| Medium Rare Catering Co. Limited | Real estate | 1978 |
| Medtech Media Limited | Information & communication | 2021 |
| Megalist Limited | Administrative & support | 2012 |
| Megan Alldridge Productions Limited | Information & communication | 2024 |
| Megs Decorating Limited | Construction | 2017 |
| Megstar Ltd | Extraterritorial | 2012 |
| Melbourne Court (Surbiton) Residents Association Limited | Households | 1971 |
| Melgrove Limited | Professional & scientific | 2019 |
| Melt for Health Limited | Health & social care | 2018 |
| Melvyn William Holdings Limited | Real estate | 2021 |
| Memphis Belles Ltd | Other services | 2017 |
| Menomatters Ltd | Professional & scientific | 2022 |
| Meor Global Ltd | Wholesale & retail | 2025 |
| Meraki Studios (Pilates) Ltd | Arts & recreation | 2026 |
| Merco Consultancy Ltd | Information & communication | 2021 |
| Mercury FOX Limited | Information & communication | 2022 |
| Merland Consultants Limited | Information & communication | 2007 |
| Merrie England Limited | Real estate | 2015 |
| Merrow Scientific Limited | Wholesale & retail | 2004 |
| Mesa Trade Ltd | Wholesale & retail | 2025 |
| Message Homes Limited | Real estate | 2024 |
| Messiah.& Co Limited | Health & social care | 2013 |
| Metcalfe Ventures Ltd | Information & communication | 2018 |
| Metrel UK Limited | Manufacturing | 1997 |
| MEW Electrical Installations Ltd | Construction | 2012 |
| Meyler Campbell Holdings Limited | Financial services | 2021 |
| Meyler Campbell Limited | Professional & scientific | 1999 |
| Mezmar Ltd | Hospitality | 2025 |
| MF Solutions Ltd | Professional & scientific | 2020 |
| Mfdf Company Ltd | Hospitality | 2026 |
| MG Apartment Management Limited | Real estate | 2017 |
| MG PMS Ltd | Professional & scientific | 2023 |
| MGB Petit Management Ltd | Households | 2017 |
| Mgeorghiou Plastering Ltd | Construction | 2025 |
| MGF Carpentry Ltd | Manufacturing | 2021 |
| MHS Schneidetechnik Ltd | Professional & scientific | 2025 |
| MI Decor Ltd | Construction | 2024 |