| Mantaline Limited | Information & communication | 1988 |
| Mantra Academy Ltd | Education | 2023 |
| Mantra Healthcare Ltd | Health & social care | 2017 |
| Mantric Studio Ltd | Wholesale & retail | 2025 |
| Manzees Ltd | Wholesale & retail | 2022 |
| Maple (182) Limited | Households | 2002 |
| Maple (184) Limited | Households | 2003 |
| Maple (194) Limited | Households | 2003 |
| Maple (217) Limited | Households | 2004 |
| Maple (259) Limited | Households | 2005 |
| Maple (282) Limited | Households | 2006 |
| Maple (354) Limited | Households | 2009 |
| Maple C Management Limited | Real estate | 2025 |
| Mapledale Properties Limited | Households | 2025 |
| Mapledene Property Holdings Limited | Households | 1977 |
| Maplehurst Crawley (Resi) LLP | | 2016 |
| Maplen Limited | Construction | 2025 |
| Mapleton Construction Ltd | Construction | 2019 |
| Mapogos Capital Holdings Ltd | Professional & scientific | 2026 |
| Maps GKS Ltd | Real estate | 2013 |
| Mapu Properties 1 Ltd | Real estate | 2025 |
| MAQ Payments Ltd | Professional & scientific | 2025 |
| MAR Couture Limited | Wholesale & retail | 2023 |
| MAR Property Estates (UK) Limited | Real estate | 2025 |
| MAR Property Services (UK) Limited | Construction | 2016 |
| Mara Building Services Ltd | Construction | 2020 |
| Marabella Ltd | Wholesale & retail | 2017 |
| Maragh Enterprises | Administrative & support | 2020 |
| Marathon House Freehold Company Limited | Real estate | 2014 |
| Marathon House RTM Company Limited | Households | 2011 |
| Marble Hill Place RES. Assoc. (Twickenham) Limited | Households | 1994 |
| Marblequay Management Company Limited | Households | 2002 |
| Marbles Services Limited | Construction | 2022 |
| Marbus Ltd | Transport & logistics | 2023 |
| March House Management Company (Kingsley Park) Limited | Real estate | 2021 |
| March Sidings Management Company Limited | Households | 2003 |
| Marco Alimentari Ltd | Wholesale & retail | 2008 |
| Marcontano Ltd | Professional & scientific | 2018 |
| Marcos Vipets Ltd | Other services | 2021 |
| Marcus Gardens Ltd | Administrative & support | 2010 |
| Marcus Lawton Ltd | Administrative & support | 2021 |
| Marden Oak Limited | Real estate | 1995 |
| Mardiv Industrial & Commercial Services Ltd | Administrative & support | 2025 |
| Marechiaro FD Limited | Hospitality | 2025 |
| Marfo Fresh Foods Ltd | Wholesale & retail | 2024 |
| Margaret's Mental Health Consultancy Limited | Health & social care | 2023 |
| Margo Estates Ltd | Real estate | 2024 |
| Maria Malena Ltd | Wholesale & retail | 2014 |
| Maria's Boutique Ltd | Wholesale & retail | 2017 |
| Maria's Health & Beauty Ltd | Health & social care | 2021 |
| Marina Lyon Wellness Coaching Limited | Health & social care | 2026 |
| Marine Engineering Experts (MEE) Ltd | Professional & scientific | 2017 |
| Mario Marko Ltd | Hospitality | 2017 |
| Maritime Calendar Ltd | Information & communication | 2022 |
| Maritime Greenwich High Road Management Company Limited | Real estate | 2016 |
| Maritime Maxillofacial Surgery Ltd | Health & social care | 2025 |
| Mark Harnett Consulting Ltd | Professional & scientific | 2019 |
| Mark Made Work Limited | Construction | 2024 |
| Mark Mechanical Limited | Professional & scientific | 2010 |
| Mark Whyte Limited | Construction | 2014 |
| Mark's H Way Ltd | Construction | 2019 |
| Markellah Healthcare Ltd | Wholesale & retail | 2025 |
| Market Intelligentsia Ltd | Wholesale & retail | 2024 |
| Market Place Solutions UK Limited | Administrative & support | 2007 |
| MARKET23 Coffee Ltd | Hospitality | 2019 |
| Marketilio Ltd | Wholesale & retail | 2025 |
| Marketing in Maritime Limited | Professional & scientific | 2020 |
| Marketing Marvels Limited | Administrative & support | 2018 |
| Markhor Homes Ltd | Transport & logistics | 2024 |
| Marko Fish House Limited | Hospitality | 2019 |
| Marks Wholesale Limited | Wholesale & retail | 2003 |
| Marksons Ltd | Extraterritorial | 2007 |
| Marla 22 Ltd | Hospitality | 2022 |
| Marlborough Court (Thatcham) Management Company Limited | Households | 2012 |
| Marlborough Place (Loughborough) Management Company Limited | Households | 2003 |
| Marlens Line Ltd | Transport & logistics | 2019 |
| Marlin Birna Limited | Wholesale & retail | 2013 |
| Marlon Legacy Homes CIC | Real estate | 2025 |
| Marlow CR Ltd | Other services | 2024 |
| Marlpark 16 CR0 Ltd | Real estate | 2020 |
| Marlpark 17 CR0 Ltd | Real estate | 2024 |
| Marlpark 275 CR0 Ltd | Real estate | 2019 |
| Marlpark 2A CR0 Ltd | Real estate | 2020 |
| Marlpark 71 HA4 Limited | Real estate | 2020 |
| Marlpark 87 CR0 Ltd | Real estate | 2020 |
| Marlpark Homes Ltd | Real estate | 2016 |
| Marlpark Limited | Financial services | 1987 |
| Marlpark Property Management Ltd | Real estate | 2018 |
| Marmsells Ltd | Wholesale & retail | 2024 |
| Marnie LUX Limited | Wholesale & retail | 2025 |
| Maroc Healthcare Limited | Health & social care | 2023 |
| Marona Shoes Limited | Wholesale & retail | 2010 |
| Maroof Ltd | Information & communication | 2013 |
| Marpat Engineering Limited | Professional & scientific | 2016 |
| Marpex Chemicals Limited | Other services | 1983 |
| Marples Grange (Blackpool) Management Company Ltd | Households | 2018 |
| Marqetly Limited | Wholesale & retail | 2026 |
| Marqueqliniq Marketing and Advertising Limited | Professional & scientific | 2020 |
| Marquis Construction Limited | Construction | 2017 |
| Marrin UK Ltd | Construction | 2012 |