| Magnum Investments Limited | Extraterritorial | 2000 |
| Mahek & ALI Ltd | Wholesale & retail | 2017 |
| Maher & Co Solicitors Limited | Professional & scientific | 2020 |
| Mahira.M Ltd | Information & communication | 2023 |
| Maid at Home Limited | Administrative & support | 2023 |
| Maida Vale Property Management Ltd | Real estate | 2025 |
| Maidenberry Healthcare Ltd | Health & social care | 2016 |
| Maidenhead & Bray Cricket Club (1996) Limited | Arts & recreation | 1996 |
| Maidenhead & Slough Tyre & Exhaust Company Limited | Wholesale & retail | 1989 |
| Maidenhead and District Chamber of Commerce Limited | Other services | 2013 |
| Maidenhead Bridge Limited | Information & communication | 2016 |
| Maidenhead Care | Administrative & support | 2009 |
| Maidenhead Community Book Festival CIC | Education | 2021 |
| Maidenhead Contracts Ltd | Professional & scientific | 2019 |
| Maidenhead Driving School Ltd | Education | 2025 |
| Maidenhead Electrical Ltd | Construction | 2015 |
| Maidenhead Engineering Ltd | Construction | 2024 |
| Maidenhead Express Ltd | Wholesale & retail | 2023 |
| Maidenhead Festival C.I.C. | Arts & recreation | 2016 |
| Maidenhead Fireplace and Stove Centre Ltd | Wholesale & retail | 2020 |
| Maidenhead Freehold Management Company Limited | Households | 1999 |
| Maidenhead Great Park CIC | Other services | 2022 |
| Maidenhead Lawn Tennis Club Limited | Arts & recreation | 2019 |
| Maidenhead Martial Arts Ltd | Arts & recreation | 2017 |
| Maidenhead Meats Ltd | Wholesale & retail | 2009 |
| Maidenhead Nails and Beauty Ltd | Other services | 2023 |
| Maidenhead Neuro Physio Limited | Health & social care | 2016 |
| Maidenhead Notary Limited | Professional & scientific | 2020 |
| Maidenhead PCN Ltd | Health & social care | 2023 |
| Maidenhead Pharmacy Limited | Wholesale & retail | 2025 |
| Maidenhead Plumbing Services Ltd | Construction | 2026 |
| Maidenhead Podiatry Limited | Health & social care | 2006 |
| Maidenhead Rowing Club Limited | Arts & recreation | 1997 |
| Maidenhead Security Limited | Administrative & support | 2016 |
| Maidenhead Shortstay Limited | Hospitality | 2017 |
| Maidenhead Skip Hire Ltd | Water & waste | 2017 |
| Maidenhead Superstore Ltd | Wholesale & retail | 2021 |
| Maidenhead Synagogue Limited | Education | 2005 |
| Maidenhead Tutorial College Limited | Education | 2023 |
| Maidenhead United FC Ltd | Arts & recreation | 2006 |
| Maidenhead Waterways Restoration Group | Other services | 2007 |
| Maidenhead Wine Company Limited | Wholesale & retail | 2002 |
| Maidenheadtherapy Ltd | Health & social care | 2022 |
| Maisie Tomlinson Marketing Services Limited | Professional & scientific | 2025 |
| MAJ Locums Ltd | Wholesale & retail | 2017 |
| Majestic Cars (UK) Limited | Transport & logistics | 2012 |
| Majestic Taxis Global Ltd | Transport & logistics | 2024 |
| Majestic Taxis Ltd | Transport & logistics | 2024 |
| Makeebo Students Limited | Administrative & support | 2006 |
| Makers Counsel Limited | Professional & scientific | 2026 |
| Making AI Work Limited | Hospitality | 2022 |
| Makway Consulting Ltd | Professional & scientific | 2026 |
| Malborough Healthcare Ltd | Health & social care | 2025 |
| Malhotra Housing Ltd | Real estate | 2024 |
| Mallards Reach (Taplow) Limited | Households | 2000 |
| Malling Keane LLP | | 2022 |
| Mamaloo's Ltd | Wholesale & retail | 2020 |
| Mamaya Tastes Limited | Wholesale & retail | 2024 |
| Mambu Tech Limited | Information & communication | 2016 |
| Mamichie Healthcare Limited | Health & social care | 2020 |
| Manacyibnomie Ltd | Construction | 2024 |
| Manchester Waste Recycling Limited | Real estate | 2004 |
| Mandau Marketing Ltd | Professional & scientific | 2004 |
| Mandolin Properties Limited | Real estate | 1999 |
| Manifold Investments Limited | Real estate | 2012 |
| Mann Management & Investments Limited | Real estate | 2015 |
| MANNA4AFRICA Ltd | Extraterritorial | 2008 |
| Manning Solutions Ltd | Administrative & support | 2000 |
| Manray Media Limited | Information & communication | 2008 |
| Manroland Goss Web Systems UK Limited | Administrative & support | 2012 |
| Manta Properties Ltd | Real estate | 2021 |
| Mantle & Llay Limited | Professional & scientific | 1983 |
| Mantra Property Group Limited | Real estate | 2021 |
| Manu Care Limited | Health & social care | 2022 |
| Manyana Enterprises Limited | Professional & scientific | 2024 |
| MAP VFX Productions Ltd | Professional & scientific | 2024 |
| Maple & Mcguire Media Ltd | Information & communication | 2026 |
| Maple Close Management Limited | Households | 1999 |
| Maplefink Ltd | Information & communication | 2014 |
| Maralb Construction Ltd | Construction | 2023 |
| Marbel Resources Limited | Professional & scientific | 2011 |
| Marble & Stone Renovation Limited | Construction | 2019 |
| Marbles Movement and Learning Limited | Education | 2014 |
| Marc Baxter Ltd | Extraterritorial | 2025 |
| Marc Daniels Specialist Recruitment Limited | Administrative & support | 2007 |
| Marcell Auto's Ltd | Wholesale & retail | 2023 |
| Marcin Musial Ltd | Hospitality | 2024 |
| Marcory Advisors Limited | Administrative & support | 2022 |
| Maria Flowers Ltd | Wholesale & retail | 2025 |
| Mariam H Ltd | Health & social care | 2014 |
| Mariinsky Limited | Financial services | 1996 |
| Marija Consulting Ltd | Administrative & support | 2024 |
| Mariners Residents Association Limited(The) | Households | 1983 |
| Mark Abbott Consultancy Limited | Professional & scientific | 2018 |
| Mark Alive Community Limited | Arts & recreation | 2017 |
| Mark Stephen Marengo International Limited | Wholesale & retail | 2005 |
| Markco Ltd | Transport & logistics | 2020 |
| Marketing Advisers (MA) Ltd | Administrative & support | 2021 |
| Marketing Business Limited | Extraterritorial | 1989 |
| Marketing DUE Diligence Limited | Extraterritorial | 2009 |