| Marcus Neiman Limited | Construction | 2019 |
| Mardulvio Ltd | Information & communication | 2019 |
| Mare to Groom Ltd | Wholesale & retail | 2022 |
| Mareb Limited | Construction | 2018 |
| Margaret House Care Home Ltd | Health & social care | 2014 |
| Margaret Logistics Ltd | Transport & logistics | 2025 |
| Margaret Solutions Limited | Information & communication | 2010 |
| Margaret SPV Ltd | Real estate | 2021 |
| Margiana Ltd | Wholesale & retail | 2023 |
| Margsd Limited | Health & social care | 2018 |
| Maria & Simona Sweets Ltd | Manufacturing | 2023 |
| Maria Jacinta Phillip Limited | Hospitality | 2024 |
| Maria's Market Cafe Ltd | Hospitality | 2003 |
| Maria's Market Square Limited | Hospitality | 2025 |
| Marian -Dani Construction Ltd | Construction | 2022 |
| Marian Tudorache Limited | Construction | 2007 |
| Marianne Chipango Limited | Health & social care | 2015 |
| Marie Kaps Ltd | Real estate | 2025 |
| Mariendiawar Care UK Ltd | Health & social care | 2023 |
| Marigold Hire Services Ltd | Administrative & support | 2024 |
| Marika Services Limited | Wholesale & retail | 2019 |
| Marine Fishing Limited | Agriculture & fishing | 2025 |
| Mario B Developments Ltd | Construction | 2019 |
| Mario Fire Ltd | Construction | 2011 |
| Marisola Parlour Ltd | Manufacturing | 2020 |
| Marium’S Optics Limited | Wholesale & retail | 2025 |
| Mariya Cleaning Ltd | Administrative & support | 2015 |
| Mark & Construct Ltd | Construction | 2023 |
| Mark & Mark Construction Ltd | Construction | 2023 |
| Mark Davies Seeds Ltd | Wholesale & retail | 2014 |
| Mark Hudson Roofing Limited | Construction | 1997 |
| Mark's Contractors Ltd | Construction | 2020 |
| Markanche IT Ltd | Information & communication | 2025 |
| Market Heaven Limited | Wholesale & retail | 2026 |
| Market House (Harlow) Limited | Households | 2025 |
| Market Place Romford Management Company Limited | Real estate | 2004 |
| Marketing Reach Ltd | Professional & scientific | 2025 |
| Markets Media Europe Ltd | Information & communication | 2012 |
| Markets Media Publishing Limited | Information & communication | 2013 |
| Markhor Security Services Ltd | Hospitality | 2018 |
| Marks Gate Groceries Limited | Wholesale & retail | 2019 |
| Marks Gate Muslim Community | Professional & scientific | 2025 |
| Marlee Developments Ltd | Real estate | 2016 |
| Marleybeau Estates Ltd. | Financial services | 2023 |
| Marnew Limited | Professional & scientific | 2026 |
| Marnie Dickens Limited | Arts & recreation | 2016 |
| Marola Expert Services Ltd | Construction | 2021 |
| MAROOT2 Ltd | Wholesale & retail | 2024 |
| Marpri Holdings Limited | Financial services | 2014 |
| Marr Group Ltd | Construction | 2015 |
| Marrkobuild Cratus Ltd | Construction | 2020 |
| Mars Horizons Ltd | Real estate | 2025 |
| Marshal Property Ltd | Households | 2025 |
| Marshalls Park Plumbing Ltd | Construction | 2021 |
| Marsham Plumbing & Heating Ltd | Construction | 2018 |
| Marsland Commercial Ltd | Professional & scientific | 2025 |
| Mart Car Parts Ltd | Wholesale & retail | 2021 |
| Martello AI Services Ltd | Information & communication | 2026 |
| Martello Manor Hythe Ltd | Health & social care | 2025 |
| Martflow Ltd | Wholesale & retail | 2024 |
| Martha’S LAB Ltd | Manufacturing | 2025 |
| Martin Homes Ltd | Real estate | 2016 |
| Martin Mone Transport Ltd | Manufacturing | 2021 |
| Martindale Constructions & Interiors Ltd | Professional & scientific | 2020 |
| Martindale Pharmaceuticals Limited | Professional & scientific | 1972 |
| Martine Wright Limited | Arts & recreation | 2013 |
| Martingold Homes Limited | Real estate | 2012 |
| Martin’S Moblie Tyres Ltd | Wholesale & retail | 2025 |
| Marufos 1 Limited | Real estate | 2026 |
| Marvel Security Ltd | Construction | 2018 |
| Marvey Property Limited | Real estate | 2023 |
| Marvick Property Investments Limited | Real estate | 2024 |
| Marvin Developments Limited | Construction | 2020 |
| Marvin Recruitment Limited | Administrative & support | 2026 |
| Marvling Bros Limited | Wholesale & retail | 2013 |
| Marwaha Construction Ltd | Construction | 2023 |
| Mary Ugbeikwu Enterprises Ltd | Health & social care | 2023 |
| Maryland. Creative Quarters Ltd | Arts & recreation | 2023 |
| Marylebone Properties Limited | Real estate | 2004 |
| Marzal PVT Ltd | Information & communication | 2017 |
| MAS Direct Services Limited | Wholesale & retail | 2022 |
| Masdek Ltd | Health & social care | 2023 |
| Mash Projects Ltd | Professional & scientific | 2023 |
| Mashb Ltd | Other services | 2018 |
| Mashinze Consulting Limited | Information & communication | 2016 |
| Mashinze Limited | Real estate | 2023 |
| Mashy 34 Ltd | Real estate | 2019 |
| Masjid Noor-E-Khatame Nabuwwat Ltd | Education | 2024 |
| Mask Build Ltd | Administrative & support | 2023 |
| Mason Corporation Properties Limited | Real estate | 2014 |
| Masons Law LLP | | 2018 |
| Mass Builders (London) Ltd | Construction | 2022 |
| Mass Works Capital Ltd | Real estate | 2025 |
| Mass Works Ltd | Professional & scientific | 2024 |
| Master Alrend Ltd | Construction | 2025 |
| Master Case Display Limited | Manufacturing | 2025 |
| Master Heating Ltd | Construction | 2017 |
| Master Plumbing Ltd | Construction | 2021 |
| Master UP Limited | Other services | 2025 |
| Master Vape 24 Ltd | Wholesale & retail | 2026 |