| Manor Farms LLP | | 2007 |
| Manor Park Avenue (Princes Risborough) Management Limited | Real estate | 2010 |
| Manor Park Catering Ltd | Hospitality | 2016 |
| Manor Place (Baker Street) Management Company Limited | Households | 2002 |
| Mantle Care Ltd | Administrative & support | 2023 |
| Mantra Digital Magic Ltd | Information & communication | 2015 |
| Mapach Limited | Transport & logistics | 2017 |
| Mapasu Limited | Manufacturing | 2024 |
| Maple Homes Tiling Limited | Construction | 2019 |
| Maples (Aylesbury) Management Company Limited | Households | 1986 |
| Mapp (UK) Limited | Administrative & support | 1987 |
| Mapp Limited | Administrative & support | 2001 |
| Maqhan UK Ltd | Wholesale & retail | 2019 |
| Maraghnaya Solutions Limited | Information & communication | 2025 |
| Marand Court Freehold Ltd. | Construction | 2011 |
| Marcelo Limited | Financial services | 2019 |
| Marcin Winski Limited | Transport & logistics | 2013 |
| Marck Construction Ltd | Construction | 2017 |
| Marcusmarc Ltd | Public administration | 2023 |
| Marescal Ghent Limited | Wholesale & retail | 2015 |
| Margintrip Limited | Transport & logistics | 1986 |
| Mari's House and Garden Ltd | Construction | 2016 |
| Marilec Electrical Services Limited | Construction | 2011 |
| Marine Environmental Monitoring Solutions Ltd | Information & communication | 2016 |
| Marius Udrea Ltd | Transport & logistics | 2025 |
| Mariyah Ltd | Construction | 2024 |
| Mark Andrews Electrical Services Ltd | Energy | 2017 |
| Mark Birch Advisory Ltd | Professional & scientific | 2026 |
| Mark Bowers HR Consulting Ltd | Professional & scientific | 2025 |
| Mark Charman Haulage Ltd | Transport & logistics | 2025 |
| Mark Eaton HR Services Limited | Professional & scientific | 2021 |
| Mark Investments Limited | Real estate | 1985 |
| Mark Leslie Productions Ltd | Information & communication | 2003 |
| Mark Weighell Consulting Limited | Information & communication | 2016 |
| Markat Distribution Limited | Transport & logistics | 2016 |
| Market House Books Limited | Information & communication | 1981 |
| Marketcore Ltd | Wholesale & retail | 2022 |
| Markiewicz Martial Arts Ltd | Arts & recreation | 2024 |
| Markify Limited | Information & communication | 2019 |
| Marlborough Developments Limited | Construction | 1996 |
| Marley Holmes Taekwondo Ltd | Arts & recreation | 2025 |
| Marlin Consultancy Ltd | Professional & scientific | 2026 |
| Marlow Performance Cars Limited | Wholesale & retail | 2006 |
| Marlow Transporter Vans Limited | Wholesale & retail | 2021 |
| Marmaduke Estates Limited | Real estate | 2005 |
| Marquees & Pavilions Limited | Administrative & support | 2012 |
| Marrian Ltd | Construction | 2016 |
| Mars Software Solutions Limited | Information & communication | 2007 |
| Mars-Hill (Aylesbury) Limited | Health & social care | 2010 |
| Marsh Court Flat Management (Moreton) Limited | Households | 1976 |
| Marsh Hill Farm Limited | Agriculture & fishing | 1973 |
| Martell Arts and Publications Limited | Information & communication | 2005 |
| Martin Godfrey Electrical Limited | Construction | 2008 |
| Martin Langley Driving School Ltd | Education | 2025 |
| Martin Paul Limited | Real estate | 1987 |
| Martin Skinner Professional Coaching Limited | Education | 2024 |
| Martin Software Ltd | Other services | 2019 |
| Martindale Electrical Limited | Construction | 2021 |
| Martindale Maintenance Limited | Construction | 2026 |
| Martinez Properties Ltd | Real estate | 2023 |
| Marvel Electrics Ltd | Energy | 2018 |
| Mary Lois Ltd | Health & social care | 2014 |
| MAS Earthworks Ltd | Construction | 2022 |
| Masawi Limited | Health & social care | 2016 |
| Mashworks Automotive Ltd | Wholesale & retail | 2025 |
| Mason Agricultural Limited | Financial services | 2016 |
| Mason Plumbing and Heating Limited | Construction | 2015 |
| Masoneet & Co Property Ltd | Households | 2025 |
| Masspecs Scientific Ltd | Wholesale & retail | 2019 |
| Massupplements Limited | Wholesale & retail | 2024 |
| Master Transportation Services Ltd | Transport & logistics | 2025 |
| Masterdriver Limited | Wholesale & retail | 2006 |
| Mastertek Services Ltd | Manufacturing | 2019 |
| Matcha Wholesale Ltd | Wholesale & retail | 2025 |
| Matera Property Investments Ltd | Construction | 2017 |
| Matey Clothing Ltd | Wholesale & retail | 2022 |
| Mathewlynn Consultancy Limited | Professional & scientific | 2026 |
| Mathias Brick and Flint Limited | Construction | 2009 |
| Mathsci Education Centre LLP | | 2024 |
| Mathsci Education Centre PVT Ltd | Education | 2017 |
| Matilda's Cafe Ltd | Hospitality | 2024 |
| Matilda’S Group Ltd | Hospitality | 2026 |
| Matina Curtis Ltd | Health & social care | 2022 |
| Matrix Fire & Security Limited | Administrative & support | 2003 |
| Matrix Fire & Security Systems Ltd | Other services | 2017 |
| Matrix FM Ltd | Administrative & support | 2026 |
| Matt Raden Podiatry Ltd | Health & social care | 2024 |
| Matt Towell Management Ltd | Arts & recreation | 2007 |
| Matthew Freeman Joinery Limited | Manufacturing | 2017 |
| Matthew Ringland Creative Limited | Professional & scientific | 2013 |
| Matthew Russell Homes Ltd | Hospitality | 2016 |
| Mature Care Limited | Health & social care | 2024 |
| Maudsley Associates Ltd | Professional & scientific | 2015 |
| MAW ICT Solutions Limited | Information & communication | 2012 |
| Mawle Court Management Company Ltd | Households | 2017 |
| MAX Secure Services Limited | Administrative & support | 2019 |
| MAX Williams Ltd. | Information & communication | 2017 |
| Maximum Estates Limited | Real estate | 2025 |
| Maximum Technologies Ltd | Information & communication | 2021 |
| Maxtekx Limited | Information & communication | 2024 |