| Made in Pebmarsh Ltd | Wholesale & retail | 2018 |
| Made of Metl Ltd | Wholesale & retail | 2025 |
| Madecube Ltd | Construction | 2018 |
| Madeleine Gardens Management Company Limited | Households | 2024 |
| Madison Management (UK) Limited | Other services | 1998 |
| Madisons Hair and Beauty Ltd | Other services | 2024 |
| Mads Management Ltd | Construction | 2019 |
| Madson Air Conditioning Limited | Construction | 1999 |
| MAE Gardens Consultancy Limited | Administrative & support | 2026 |
| MAE Gardens Ltd | Administrative & support | 2022 |
| MAE Property Services Limited | Construction | 2023 |
| Magdalen Hall Company Limited | Real estate | 2002 |
| Magelan Limited | Construction | 2006 |
| Magic Car Wash and Valeting Ltd | Wholesale & retail | 2020 |
| Magicspacecleaning Ltd. | Administrative & support | 2025 |
| Magma Competitions Ltd | Wholesale & retail | 2025 |
| Magma Investment Limited | Wholesale & retail | 2007 |
| Magna Carpentry Ltd | Manufacturing | 2025 |
| Magnet Services Limited | Wholesale & retail | 1980 |
| Magnusport Limited | Arts & recreation | 2021 |
| Maguire Roofing Limited | Administrative & support | 2013 |
| Magura Cars Ltd | Wholesale & retail | 2025 |
| MAH Pipe Contractors Limited | Construction | 2017 |
| Maha Retail Limited | Wholesale & retail | 2015 |
| Mahala Sauna Limited | Wholesale & retail | 2025 |
| Maharani Indian Restaurant COL Ltd | Hospitality | 2022 |
| Maharani Millions Colchester Limited | Wholesale & retail | 2025 |
| Mahek Enterprice Limited | Health & social care | 2016 |
| Maia Developments Ltd. | Construction | 2020 |
| MAID2CLEAN (Colchester) Ltd | Administrative & support | 2012 |
| Mail Boxes ETC. Colchester Limited | Administrative & support | 2009 |
| Mainas Limited | Health & social care | 2016 |
| Mains 2 Power Electrical Limited | Construction | 2006 |
| Mainstage Productions Limited | Arts & recreation | 2017 |
| Mainstream Construction Limited | Construction | 2014 |
| Maintenance First Limited | Administrative & support | 2011 |
| Maison Care Ltd | Health & social care | 2012 |
| Maison Louvain Limited | Professional & scientific | 2024 |
| Maiti Homes Limited | Real estate | 2025 |
| Major Ninth Ltd | Professional & scientific | 2018 |
| MAK Engineering Services Limited | Professional & scientific | 2016 |
| Makao Investment Limited | Real estate | 2020 |
| Makarios Global Services Ltd | Construction | 2023 |
| Makarios Ventures Limited | Professional & scientific | 2023 |
| Make a Smile Lottery Ltd | Arts & recreation | 2017 |
| Make IT Happen Limited | Professional & scientific | 2021 |
| Make IT Special Essex Limited | Other services | 2026 |
| Make Thyme for Paws Limited | Wholesale & retail | 2023 |
| Makepeace Plumbing and Heating Ltd | Construction | 2023 |
| Makeright Financial Solutions Limited | Administrative & support | 2010 |
| Making Aces Limited | Arts & recreation | 2006 |
| Maks Incorporated Limited | Real estate | 2019 |
| Malaxmi PVT Ltd | Real estate | 2024 |
| Maldon Carpet Flooring Warehouse Limited | Construction | 2009 |
| Maldon Coffee Company Ltd | Wholesale & retail | 2024 |
| Maldon Coffee Shop Ltd | Hospitality | 2018 |
| Maldon Electric Securities,Limited | Financial services | 1932 |
| Maldon Heating Services Ltd | Construction | 2024 |
| Maldon Life Ltd | Extraterritorial | 2013 |
| Maldon Motel Limited | Other services | 2015 |
| Maldon Road Limited | Real estate | 2007 |
| Maldon Scaffolding Services Limited | Construction | 2018 |
| Maleek OYE Ltd | Arts & recreation | 2025 |
| Mallard Consolidated Limited | Financial services | 2014 |
| Mallard Leasing Limited | Financial services | 1992 |
| Mallott Telecom Limited | Information & communication | 2019 |
| Mallows Roofing Limited | Construction | 2001 |
| Malting Farm Ltd | Hospitality | 2020 |
| Maltron International Limited | Manufacturing | 1996 |
| Maltstore Management Company Limited | Households | 2005 |
| Malure Group Limited | Construction | 2026 |
| Malyon Plumbing & Heating Limited | Construction | 2024 |
| Mama Cook Thai Catering Ltd | Hospitality | 2025 |
| Mama Tee's Tasty Kitchen Ltd | Wholesale & retail | 2026 |
| Mama's Bistro Limited | Hospitality | 2026 |
| Mambjo Media Ltd | Professional & scientific | 2016 |
| Mamma MIA (Colchester) Ltd | Hospitality | 2016 |
| Mammal Conservation Trust Limited(The) | Professional & scientific | 1979 |
| MAN About Town Barbers Ltd | Other services | 2019 |
| Management Systems UK Limited | Information & communication | 1998 |
| Manam Foods Ltd | Administrative & support | 2025 |
| Manda Business Group Ltd | Professional & scientific | 2025 |
| Mandaz Productions Limited | Arts & recreation | 2006 |
| Mane Construction Solutions Ltd | Construction | 2024 |
| Manex Utility Services Limited | Manufacturing | 2003 |
| Manganga Productions Ltd | Professional & scientific | 2014 |
| Mango Hair Design Limited | Other services | 2014 |
| Mango Media Group Ltd | Professional & scientific | 2025 |
| Mango PIE Ltd | Administrative & support | 2007 |
| Mangopanda Ltd | Arts & recreation | 2025 |
| Mangos Hand Car Wash and Valeting Ltd | Manufacturing | 2020 |
| Mani Hospitality Ltd | Hospitality | 2026 |
| Manig Business Advice and Training Limited | Administrative & support | 2008 |
| Manimpex (Holdings) Limited | Professional & scientific | 2015 |
| Manimpex Management Limited | Manufacturing | 2001 |
| Manimpex Online Limited | Extraterritorial | 2015 |
| Manimpex Recruitment Limited | Extraterritorial | 2015 |
| Manimpex Trading Limited | Extraterritorial | 2015 |
| Manke Markets U.K. Limited | Hospitality | 2005 |
| Mann Dental Care Limited | Health & social care | 2012 |