| Middlesex Heating & Plumbing Services Limited | Construction | 2021 |
| Middlesex Mobile Tyres Limited | Wholesale & retail | 2018 |
| Middlesex Plant Hire Ltd | Construction | 2023 |
| Middlesex Recycling Limited | Water & waste | 2014 |
| Middlesex Roof Repairs Ltd | Construction | 2013 |
| Middlesex Waste Management Limited | Water & waste | 2017 |
| Midiasolutions Limited | Health & social care | 2015 |
| Midland NN Properties Limited | Construction | 2025 |
| MIFEED1 Limited | Professional & scientific | 2023 |
| MIG27 Services Limited | Manufacturing | 2023 |
| MII Consulting Limited | Professional & scientific | 2023 |
| Mikaworks Studio Ltd | Professional & scientific | 2025 |
| Mike Francis Art Ltd | Arts & recreation | 2023 |
| Mike Massey Associates LLP | | 2015 |
| Mikjul Developments Limited | Agriculture & fishing | 2022 |
| Milan Spedition Ltd | Construction | 2025 |
| Milcol Plumbing and Heating Limited | Construction | 2017 |
| Milestone Constructions Limited | Construction | 1998 |
| Milkwood Furniture Ltd | Manufacturing | 2021 |
| Mill Lane Freehold Limited | Real estate | 2023 |
| Millcroft Wealth Management Limited | Professional & scientific | 2011 |
| Miller and Miller Properties Ltd | Real estate | 2024 |
| Millhouse Landscape Design and Build Limited | Administrative & support | 2018 |
| Millhouse Leasing Limited | Financial services | 2004 |
| Millie Moses London Ltd | Wholesale & retail | 2025 |
| Millionaires' Mentor Ltd | Professional & scientific | 2018 |
| Millstone Meadow Limited | Construction | 2021 |
| Milo Couture Limited | Wholesale & retail | 2019 |
| Min-E-Moke Ltd | Wholesale & retail | 2018 |
| Minas Productions Limited | Information & communication | 2010 |
| Mind Drive Ltd | Health & social care | 2025 |
| Mind Muscle Clinic Ltd | Other services | 2021 |
| Mind Muscle Fitness Ltd | Arts & recreation | 2023 |
| Mindstream Digital Limited | Wholesale & retail | 2025 |
| Minervapro Limited | Professional & scientific | 2011 |
| Mingle & Munch Ltd | Hospitality | 2024 |
| Minnetta Ltd | Other services | 2019 |
| Mint Sauce LDN Ltd | Wholesale & retail | 2020 |
| Mira Beauty Lounge Ltd | Other services | 2026 |
| Miracle Farming Ltd | Wholesale & retail | 2019 |
| Mirage Manor Properties Ltd | Real estate | 2024 |
| Mirai Karate Dojo Ltd | Arts & recreation | 2022 |
| Miraj Beers & Wines Limited | Wholesale & retail | 2013 |
| Mirus Management Services Limited | Professional & scientific | 2015 |
| Mission Appliances Limited | Construction | 2019 |
| Mission Aviation Fellowship International | Transport & logistics | 1996 |
| Mission Glazing Ltd | Construction | 2020 |
| Mission Repair Limited | Construction | 2019 |
| Mister BLY Limited | Other services | 2010 |
| Mitanium Group Holdings Ltd | Professional & scientific | 2024 |
| Mitanium Group Services Ltd | Administrative & support | 2024 |
| Mitanium Ltd | Manufacturing | 2020 |
| Mitanium Manufacturing Ltd | Manufacturing | 2024 |
| Mitanium Rental Ltd | Administrative & support | 2024 |
| Mitford Ltd | Professional & scientific | 2021 |
| Mitras Global Limited | Extraterritorial | 2023 |
| Mittsu Sushi Ltd | Hospitality | 2024 |
| Mittsu Ventures Holdings Ltd | Financial services | 2025 |
| Mitzpah Investments Limited | Financial services | 2012 |
| MJ Kent Enterprises Limited | Real estate | 2024 |
| MJ Monaco Ltd | Wholesale & retail | 2020 |
| MJD Bars Limited | Hospitality | 2025 |
| MJD Building and Landscaping Ltd | Construction | 2021 |
| MJD Properties UK Limited | Real estate | 2018 |
| MJD Property Limited | Real estate | 2025 |
| MJD Trading Limited | Financial services | 2012 |
| MJD Wealth Limited | Financial services | 2019 |
| Mjfs Holdings Ltd | Financial services | 2026 |
| MJH Consulting Services Limited | Administrative & support | 2021 |
| MJI Traders Ltd | Transport & logistics | 2026 |
| MJJ Jewellery Limited | Wholesale & retail | 2025 |
| MJM Forestry and Land Clearance Limited | Administrative & support | 1999 |
| MJN Gardening Limited | Administrative & support | 2012 |
| MJO Controls Limited | Professional & scientific | 2016 |
| MJS Housing Private Company Ltd | Real estate | 2024 |
| MJS Plant Service & Repair Limited | Manufacturing | 2015 |
| Mjsb Ltd | Information & communication | 2026 |
| MJV Properties Ltd | Real estate | 2014 |
| MK Decorators Ltd | Construction | 2007 |
| MK Portland Ltd | Education | 2023 |
| MK Sparkling Carwash Ltd | Administrative & support | 2024 |
| MK Window Cleaning Services Ltd | Administrative & support | 2020 |
| MK Wire Ltd | Construction | 2019 |
| MKG Hospitality Ltd | Administrative & support | 2005 |
| MKK Consultancy Limited | Information & communication | 2016 |
| Mkmfb Ltd | Construction | 2019 |
| MKO Limited | Health & social care | 2023 |
| MKS Electrical Limited | Construction | 2015 |
| ML Brickwork Limited | Construction | 2019 |
| ML Cleaning and Maintenance Services Limited | Administrative & support | 2022 |
| ML Flooring Solutions Limited | Construction | 2025 |
| ML Safety Management Limited | Administrative & support | 2022 |
| MLE (Ashford) Limited | Arts & recreation | 2012 |
| Mlia Investments Limited | Real estate | 2025 |
| MM Cash & Carry Ltd | Hospitality | 2019 |
| MM Consult Group Limited | Information & communication | 2026 |
| MM Halal Meat Limited | Wholesale & retail | 2026 |
| MM Mixologie Ltd | Hospitality | 2026 |
| MM Payments Ltd | Financial services | 2024 |
| MM Plumbing Heating & Electrical Services Ltd | Construction | 2018 |