| Mackays of Cambridge Holdings Limited | Construction | 2009 |
| Mackwes Ltd | Real estate | 2020 |
| Maclin Consultancy Ltd | Real estate | 2018 |
| Macondo Ltd | Financial services | 2011 |
| Macpost Limited | | 1984 |
| Macsmith Property Holdings Ltd | Construction | 2021 |
| Mactavish Health Assessments Limited | Health & social care | 2019 |
| Madair Ltd | Manufacturing | 2026 |
| Madara Cosmetics Ltd | Wholesale & retail | 2024 |
| Maddison Consulting Limited | Professional & scientific | 2012 |
| Maddocks Healthcare Ltd | Health & social care | 2012 |
| Maddox House Freehold Limited | Households | 2019 |
| Made Headway Limited | Information & communication | 2008 |
| Made in Great Britain Campaign Ltd | Other services | 2013 |
| Made Victorian Ltd | Manufacturing | 2022 |
| Made YOU Look Beautiful Limited | Other services | 2020 |
| MADE4NET Ltd | Wholesale & retail | 2020 |
| Madina Fresh Foods Ltd | Wholesale & retail | 2026 |
| Madingley Developments Ltd | Construction | 2015 |
| Madison Decor Limited | Construction | 2006 |
| Madknight Games Studios Ltd | Professional & scientific | 2025 |
| Madras Restaurant Limited | Extraterritorial | 2019 |
| Madsan Homes Ltd | Real estate | 2023 |
| Maedoran Limited | Other services | 2013 |
| Maersk East Limited | Transport & logistics | 2025 |
| Mafinica Electrical Ltd | Construction | 2021 |
| Mafuslam Ltd | Manufacturing | 2026 |
| MAG (UK) Services Cambridge Ltd | Other services | 2022 |
| MAG Edtech Limited | Information & communication | 2024 |
| Magenti Methodologies Ltd | Professional & scientific | 2026 |
| Maggie's Farm Shop Limited | Wholesale & retail | 2020 |
| Magic 2 Media Limited | Information & communication | 2015 |
| Magic Maker Group Corp., Ltd | Wholesale & retail | 2016 |
| Magic Monkey Limited | Administrative & support | 2010 |
| Magic Spiral Limited | Wholesale & retail | 2024 |
| Magical Trading and Technology Limited | Wholesale & retail | 2025 |
| Magma Communications Ltd | Information & communication | 2022 |
| Magmore Marine Limited | Manufacturing | 2024 |
| Magna Bottling Limited | Manufacturing | 2004 |
| Magna Brewery Limited | Manufacturing | 2004 |
| Magna Frequency Components Limited | Wholesale & retail | 1988 |
| Magnus Burt Property Limited | Real estate | 2025 |
| Magog Farm Limited | Agriculture & fishing | 1959 |
| Magog Farm Management Limited | Administrative & support | 2000 |
| Magpicians Limited | Information & communication | 2011 |
| Magus Management Limited | Construction | 2018 |
| MAH AST1 Ltd | Real estate | 2022 |
| MAH Bloodstock Ltd | Agriculture & fishing | 2022 |
| Mahana Limited | Professional & scientific | 2008 |
| Mahrin Limited | Professional & scientific | 2024 |
| MAI Communications Ltd | Administrative & support | 2024 |
| MAI Corporation Ltd | Construction | 2024 |
| Main Electrical & Appliance Services Ltd | Manufacturing | 2019 |
| Mairol GmbH Co., Ltd | Extraterritorial | 2021 |
| Maison Bengal Limited | Wholesale & retail | 2004 |
| Maison Caniche Ltd | Wholesale & retail | 2025 |
| Maison Clement Bakery & Patisserie Limited | Hospitality | 2014 |
| Maison Clement Bakery&Patisserie Newnham Limited | Hospitality | 2019 |
| Maison Gomm Ltd | Construction | 2021 |
| Maison Invest Ltd | Real estate | 2015 |
| Maison Rental Ltd | Real estate | 2023 |
| Majek EYE Limited | Professional & scientific | 2023 |
| Majestique Properties Ltd | Hospitality | 2013 |
| Majico Ltd | Water & waste | 2019 |
| Major Bench Limited | Real estate | 2025 |
| Major Kane Ltd | Wholesale & retail | 2025 |
| Major Seventh Limited | Information & communication | 2007 |
| Majorflight Ltd | Manufacturing | 2025 |
| MAK Agri Ltd | Professional & scientific | 2025 |
| Mak-Hannah Projects Ltd | Information & communication | 2024 |
| Makani Cambridge CIC | Professional & scientific | 2024 |
| Makao LLP | | 2020 |
| Make Trade Ltd | Wholesale & retail | 2025 |
| Make, DO and Mend | Health & social care | 2011 |
| Makely Software Ltd | Information & communication | 2019 |
| Makespace Cambridge Limited | Professional & scientific | 2010 |
| Makethrough Ltd | Arts & recreation | 2021 |
| Makkah International Trading Co., Ltd | Extraterritorial | 2015 |
| Maktaba Ltd | Information & communication | 2019 |
| Mala World Ltd. | Hospitality | 2024 |
| Malabar Fresh Foods Limited | Wholesale & retail | 2025 |
| Malco Services Limited | Administrative & support | 2010 |
| Malcolm Close RTM Company Limited | Real estate | 2010 |
| Malcolm Reed Construction Limited | Construction | 2002 |
| Malebox Health Ltd | Information & communication | 2019 |
| Males Property Limited | Real estate | 2022 |
| Mallard Place Management Company Limited | Households | 2007 |
| Malley Medical Ltd | Health & social care | 2023 |
| Mallory House Estate Management Company Limited | Households | 2015 |
| Malta Aircraft Engineering Services Ltd | Manufacturing | 2024 |
| Maltings Fish & Chips (Baldock) Ltd | Hospitality | 2017 |
| Malvern View Properties Ltd | Real estate | 2024 |
| Malvic Construction Ltd | Construction | 2025 |
| Mamade Ltd | Wholesale & retail | 2020 |
| Mamas WHO Brunch Ltd | Administrative & support | 2026 |
| Mambery Limited | Wholesale & retail | 2019 |
| Mamelok Papercraft Limited | Manufacturing | 2009 |
| Mami on Mami Ltd | Manufacturing | 2021 |
| MAN Farming Limited Partnership | | 2026 |
| MAN N Van and Furniture Limited | Transport & logistics | 2026 |