| Mann Smith Holdings Limited | Financial services | 2018 |
| Mann Smith Limited | Professional & scientific | 2018 |
| Manni Ltd | Hospitality | 2018 |
| Manning Roofing Limited | Construction | 2025 |
| Manor Farm Cottages Management Co Limited | Households | 2004 |
| Manoukianpaedsortho Healthcare Ltd | Health & social care | 2023 |
| Mantal Limited | Real estate | 2016 |
| Mantle Healthcare Limited | Health & social care | 2016 |
| Manufacturing Technology (UK) Limited | Professional & scientific | 2008 |
| Maple Orthodontics Ltd | Health & social care | 2020 |
| Mapleblue Ltd | Information & communication | 2000 |
| Maplerock Properties Limited | Real estate | 2015 |
| Maples (NO.2) Maintenance Company (Hitchin) Limited(The) | Households | 1973 |
| MAR Cooling Solutions Limited | Manufacturing | 2020 |
| Marble Arch Dental Centre Ltd | Health & social care | 2007 |
| Marble Arch Medical Centre Limited | Health & social care | 1991 |
| Marcaudz Ltd | Real estate | 2025 |
| Marchfield Developments Limited | Extraterritorial | 2025 |
| Marchfield Group Limited | Extraterritorial | 2025 |
| Marchfield Homes Limited | Extraterritorial | 2025 |
| Marchfield Management Services LLP | | 2006 |
| Marchfield Properties Holdings Ltd | Financial services | 2016 |
| Marchfield Properties Limited | Real estate | 2004 |
| Marcos & Pusung Estate Ltd | Real estate | 2026 |
| Marcus Rowland Limited | Arts & recreation | 2002 |
| Mariana Moise Ltd | Health & social care | 2017 |
| Marigold Limited | Health & social care | 2020 |
| Marina Hughes Interiors Ltd | Other services | 2022 |
| Marina Luxury Lettings Limited | Real estate | 2023 |
| Mario Management Ltd | Construction | 2015 |
| Maritime & Offshore Consultants Limited | Professional & scientific | 2003 |
| Maritime Ltd | Professional & scientific | 2025 |
| Mark Chapman Consulting Limited | Professional & scientific | 2017 |
| Marketplace Dynamics Limited | Wholesale & retail | 2023 |
| Markets VOX Ltd | Information & communication | 2018 |
| Marky's Scaffolding & Rigging Services Ltd | Construction | 2021 |
| Marmi Design Ltd | Construction | 2012 |
| Marmite Catering Private Chef Ltd | Hospitality | 2025 |
| Marmite Fine Dining Catering Limited | Hospitality | 2018 |
| Marsden Acquisitions Ltd | Financial services | 2023 |
| Marsden Enterprises Limited | Professional & scientific | 1997 |
| Marsh Close Residents Company Limited | Households | 1976 |
| Marshgate Ltd | Financial services | 2018 |
| Marshmoor Bricks Limited | Wholesale & retail | 1989 |
| Marshmoor Holdings Ltd | Financial services | 2023 |
| Martin Perry Associates Limited | Administrative & support | 2012 |
| Martins Furniture Stevenage Ltd | Wholesale & retail | 2025 |
| Martogid Limited | Health & social care | 2019 |
| Marvelfairs Limited | Wholesale & retail | 1964 |
| Marylands Holdings Limited | Financial services | 2021 |
| Masala Group Ltd | Hospitality | 2019 |
| Mashandy Health Limited | Health & social care | 2013 |
| Mason Plastering & Drylining Limited | Construction | 2017 |
| Masoom Catering Ltd | Hospitality | 2025 |
| Masoom Tandoori Takeaway Ltd | Hospitality | 2026 |
| Masowe Gospel of GOD Church Ltd | Other services | 2013 |
| Masters BM Ltd | Construction | 2016 |
| Masterson Brothers Limited | Real estate | 2024 |
| MAT Track Ltd | Information & communication | 2025 |
| Mata London Limited | Construction | 2019 |
| Mata Property Group Ltd | Real estate | 2026 |
| Match VFX Limited | Other services | 2014 |
| Matei & Pricope Ltd | Transport & logistics | 2021 |
| Matendo Ltd | Health & social care | 2018 |
| Mathurika Ltd | Real estate | 2025 |
| Matilda Medical Limited | Health & social care | 2018 |
| Matloob Neuro Limited | Health & social care | 2025 |
| Mats Professional Services Ltd | Professional & scientific | 2010 |
| Matt Vosper Photography Ltd | Information & communication | 2013 |
| Matt Warren Holdings Ltd | Professional & scientific | 2025 |
| Matterhorn Investments Limited | Real estate | 2008 |
| Matthew Gill Transport Limited | Transport & logistics | 2017 |
| Matthew Hill Bespoke Ltd | Manufacturing | 2017 |
| Matthews Investments Ltd | Real estate | 2026 |
| Mattmall Property Ltd | Real estate | 2023 |
| Matty Mccabe Grips Ltd | Information & communication | 2025 |
| Mauglo Limited | Real estate | 2025 |
| Maven Bathrooms & Interiors Ltd | Construction | 2009 |
| Maven Consultants Limited | Administrative & support | 2019 |
| Maven E&L Ltd | Professional & scientific | 2019 |
| Maven Projects Limited | Professional & scientific | 2020 |
| Maven Tax Services Limited | Professional & scientific | 2026 |
| Maverick Magicians Limited | Arts & recreation | 2024 |
| Mavi Health Ltd | Health & social care | 2025 |
| Mavi Utopia Properties Ltd | Real estate | 2025 |
| MAX Blueman Group Limited | Construction | 2024 |
| MAX Rushden Limited | Information & communication | 2008 |
| Maxgti Education Limited | Education | 2026 |
| Maya Property Solutions Ltd | Households | 2024 |
| Maygroup Property Limited | Real estate | 2025 |
| Mayor Productions Limited | Professional & scientific | 2018 |
| Maytrix Construction Ltd | Construction | 2009 |
| MB Antiques Ltd | Other services | 2021 |
| MB Chemistry Consulting Ltd | Professional & scientific | 2019 |
| MB Mentoring Ltd | Health & social care | 2026 |
| MB Tiler Ltd | Construction | 2019 |
| MB Windows & Doors Limited | Construction | 2019 |
| Mbbm Private Ltd | Financial services | 2025 |
| MBC Studios Ltd | Information & communication | 2024 |
| Mbcm Ltd | Construction | 2020 |