| Mackenzie Financial Limited | Financial services | 2026 |
| Mackenzies Gym Ltd | Arts & recreation | 2017 |
| Mackoz Ltd | Transport & logistics | 2026 |
| Macro Carpets Limited | Wholesale & retail | 2017 |
| Macro Edge Ltd | Wholesale & retail | 2025 |
| Macwoolf Mortgages Ltd | Financial services | 2020 |
| MAD Mortgages Ltd | Financial services | 2026 |
| MAD River Limited | Administrative & support | 2001 |
| MAD River Management Ltd | Administrative & support | 2020 |
| Madden Real Estate & Investments Ltd | Real estate | 2021 |
| Made by Physios Ltd | Wholesale & retail | 2023 |
| Madeesa Limited | Wholesale & retail | 2025 |
| Madegen Poole Limited | Hospitality | 2026 |
| Madeleines Marketing Ltd | Professional & scientific | 2026 |
| Madewo Ltd | Manufacturing | 2019 |
| Madina Motors Ltd | Wholesale & retail | 2025 |
| Madjax PUB Co Ltd | Hospitality | 2025 |
| Madjen Services Ltd | Health & social care | 2023 |
| Madmar Media Ltd | Administrative & support | 2023 |
| Maedev Limited | Wholesale & retail | 2021 |
| Mafia (Dorset) Limited | Extraterritorial | 2017 |
| Mafia Holdings Ltd | Financial services | 2023 |
| MAG Composite Ltd | Manufacturing | 2015 |
| Magaton Ltd | Professional & scientific | 2013 |
| Magb Finance Limited | Professional & scientific | 2014 |
| Magdalena Owen Limited | Health & social care | 2016 |
| Magenta Court RTM Company Ltd | Households | 2013 |
| Magenta Group Investments Limited | Financial services | 2022 |
| Magenta I Limited | Financial services | 2021 |
| Magic Cleaning Services Limited | Administrative & support | 2017 |
| Magic Little Giants Limited | Professional & scientific | 2021 |
| Magicsell Ltd | Information & communication | 2026 |
| Magna Blueflame Ltd | Construction | 2011 |
| Magna Motor Company (Christchurch) Limited | Wholesale & retail | 1999 |
| Magna Motor Company Limited | Wholesale & retail | 1982 |
| Magnax Ltd | Real estate | 2021 |
| Magni Telescopic Handlers UK Limited | Wholesale & retail | 2017 |
| Magnolia House Care Home Limited | Health & social care | 2009 |
| Magnus Estates Limited | Real estate | 1998 |
| Mahamaya Limited | Professional & scientific | 2026 |
| Mahir Korkmaz Ltd | Manufacturing | 2021 |
| Mahm Limited | Manufacturing | 2023 |
| Maia Aesthetics Limited | Other services | 2024 |
| Maia Marine Ltd | Extraterritorial | 2026 |
| Maia Properties Limited | Real estate | 2016 |
| Maid in Poole Ltd | Administrative & support | 2020 |
| MAID2CLEAN Central Manchester Ltd | Administrative & support | 2019 |
| MAID2CLEAN South Devon Limited | Administrative & support | 2025 |
| MAID2CLEAN West Cornwall Ltd | Administrative & support | 2019 |
| Maiden View Ltd | Households | 2025 |
| Maidman Enterprises (Hamworthy) Ltd | Administrative & support | 2022 |
| Maidman Enterprises Limited | Extraterritorial | 2022 |
| Mailchannels UK Ltd | Information & communication | 2013 |
| Mailstar Ltd | Professional & scientific | 1997 |
| Mainplay Limited | Administrative & support | 2012 |
| Mainsail Properties Limited | Real estate | 2021 |
| Mainspring Financial Planning Limited | Financial services | 2025 |
| Maintain UK Drains Limited | Administrative & support | 2006 |
| Mair Estate Ltd | Real estate | 2021 |
| Maison Fragrant Ltd | Wholesale & retail | 2025 |
| Maison Francaise Nannies Ltd | Administrative & support | 2026 |
| Maison Lamée Ltd | Construction | 2020 |
| Maison Sansar Limited | Professional & scientific | 2026 |
| Maison U Ltd | Real estate | 2024 |
| Maison X Consultancy Ltd | Professional & scientific | 2024 |
| Maisonelanco Ltd | Wholesale & retail | 2025 |
| Maitland Farmers Limited | Financial services | 2006 |
| Maiva Freehold Ltd | Households | 2024 |
| Maiva Ltd | Real estate | 2020 |
| Maiva Projects Limited | Construction | 2026 |
| Majal Properties Ltd | Real estate | 2022 |
| Majehoro Ltd | Information & communication | 2025 |
| Majestic ERA Ltd | Wholesale & retail | 2025 |
| Majestic One Limited | Information & communication | 2017 |
| Major PR Ltd | Professional & scientific | 2022 |
| MAK Global Holdings Limited | Financial services | 2025 |
| Maka Care Limited | Health & social care | 2020 |
| Make-More Rentals Ltd | Hospitality | 2024 |
| Maker Media Business Ltd | Information & communication | 2025 |
| Makingmedicine Ltd | Education | 2025 |
| Makisu Ltd | Hospitality | 2021 |
| Makkah Foods Ltd | Wholesale & retail | 2019 |
| Makkah Oriental Food Stores Limited | Wholesale & retail | 2014 |
| Makpit Limited | Professional & scientific | 2012 |
| Malan's Auto Services Ltd | Manufacturing | 2023 |
| Malcolm Bullock Ltd | Information & communication | 2024 |
| Maliksheikhtraders Ltd | Wholesale & retail | 2024 |
| Maliu Limited | Wholesale & retail | 2015 |
| Maliza Productions Ltd. | Information & communication | 2016 |
| Mallard Software Ltd | Information & communication | 2021 |
| Mallorcantonic Ltd | Administrative & support | 2015 |
| Mallwood Roofing Limited | Construction | 2009 |
| Malmesbury Estates Limited | Real estate | 2008 |
| Malo Collective Limited | Real estate | 2025 |
| Maloric Digital Ltd | Information & communication | 2021 |
| Maluzo Ltd | Information & communication | 2018 |
| Malyon Home Improvements Ltd | Construction | 2020 |
| MAM Blok Ltd | Wholesale & retail | 2025 |
| Mama's Boobie Box Ltd | Manufacturing | 2024 |
| Mamma MIA Bournemouth Ltd | Hospitality | 2023 |