| Masseuse Oasis Limited | Other services | 2025 |
| Massey Street RTM Company Limited | Households | 2013 |
| Massi YM Co., Ltd | Manufacturing | 2019 |
| Massimo Figarazzi Ltd | Construction | 2021 |
| Massive Chemical Technology Limited | Extraterritorial | 2024 |
| Mast Holdings Limited | Administrative & support | 2018 |
| Master Auto Parts Co., Ltd | Wholesale & retail | 2019 |
| Master Data Consultants Ltd | Professional & scientific | 2018 |
| Master Film Production Company Ltd | Information & communication | 2024 |
| Master Smith Building & Carpentry Ltd | Construction | 2025 |
| Master Your Business Ltd | Education | 2026 |
| Masthead Biosciences Limited | Professional & scientific | 2016 |
| Masum Limited | Hospitality | 2013 |
| Matahari 196 Limited | Professional & scientific | 1989 |
| MATEO2020 Ltd | Manufacturing | 2026 |
| Material Harvest Ltd | Extraterritorial | 2023 |
| Materials Nexus Limited | Professional & scientific | 2020 |
| Mathsfit Ltd | Education | 2022 |
| Mathsome Limited | Education | 2021 |
| Mathumagil Trading Ltd | Hospitality | 2024 |
| Matimba Ltd | Health & social care | 2019 |
| Matri Coaching Ltd | Administrative & support | 2024 |
| Matriqx Data Limited | Information & communication | 2025 |
| Matriqx Group Limited | Professional & scientific | 2025 |
| Matriqx Intelligence Limited | Information & communication | 2025 |
| Matriqx Investments Limited | Financial services | 2025 |
| Matriqx Life Sciences Limited | Professional & scientific | 2025 |
| Matriqx Limited | Information & communication | 2025 |
| Matriqx Services Limited | Professional & scientific | 2025 |
| Matrix Property Assets Limited | Real estate | 2021 |
| Matsolve Limited | Professional & scientific | 2020 |
| Matss Holdings Ltd | Financial services | 2026 |
| Matt Day Hair Limited | Other services | 2023 |
| Matt Evans Heating Limited | Construction | 2019 |
| Matt Harris Photography Ltd | Professional & scientific | 2011 |
| Matt Lawrence Building Contracts Limited | Construction | 2021 |
| Matt Willatt Design Ltd | Professional & scientific | 2014 |
| Matterwise Services Ltd | Wholesale & retail | 2002 |
| Matthew Gaunt Scientific Consultancy Limited | Professional & scientific | 2022 |
| Matthew Lewis Limited | Other services | 2010 |
| Maude Bros.(Contractors)Limited | Real estate | 1942 |
| MAV Technologies Ltd | Information & communication | 2012 |
| MAV9 Technologies Ltd | Information & communication | 2026 |
| Maven Garment Limited | Extraterritorial | 2011 |
| Mavenir IPA UK Limited | Professional & scientific | 1997 |
| Maverick ML Ltd | Information & communication | 2020 |
| Mavinci Dynamics Limited | Manufacturing | 2024 |
| Mavinci Limited | Wholesale & retail | 2019 |
| MAX Armstrong Design Works Ltd | Professional & scientific | 2021 |
| MAX Qautec Import and Export Co., Limited | Professional & scientific | 2023 |
| MAX Sather Ltd | Professional & scientific | 2023 |
| Maxapiens Limited | Professional & scientific | 2022 |
| Maxben Consulting Limited | Information & communication | 2009 |
| Maxgate Limited | Professional & scientific | 2021 |
| Maxibuild Management Limited | Professional & scientific | 2020 |
| Maxim Composites Ltd | Manufacturing | 2018 |
| Maxwell Sourcing Co., Ltd | Wholesale & retail | 2024 |
| MAY Construct Ltd | Construction | 2025 |
| MAY Twin Media Limited | Information & communication | 2011 |
| Maya Capital Investments Limited | Real estate | 2019 |
| Maya Constructions Limited | Administrative & support | 2003 |
| Mayfair Court (Cambridge) Residents Association Limited | Professional & scientific | 1983 |
| Mayfifteen Communications Ltd | Professional & scientific | 2011 |
| Mayfiy Co. Ltd | Manufacturing | 2025 |
| Mayflower Manhattan Limited | Construction | 1980 |
| Mayflower Takeaway Ltd | Hospitality | 2014 |
| Maynet Crossborder Limited | Manufacturing | 2025 |
| Mayway Electronics Co., Ltd | Manufacturing | 2020 |
| MAZ Road Limited | Transport & logistics | 2015 |
| Maza Hospitality Ltd | Hospitality | 2025 |
| Maze Green Ltd | Manufacturing | 2023 |
| Maze Theory Development Ltd | Information & communication | 2018 |
| Maze Theory Games Studio Ltd | Information & communication | 2026 |
| Mazzoza Limited | Financial services | 2015 |
| MB Asset Holdings Limited | Construction | 2026 |
| MB Clinical Limited | Professional & scientific | 2022 |
| MB Holdings 1 Limited | Financial services | 2026 |
| MB Tech Group Ltd | Information & communication | 2025 |
| MB2005 NO 1 Limited | Real estate | 2005 |
| MB6 Consulting Ltd | Wholesale & retail | 2026 |
| MBB Pubs Limited | Hospitality | 2020 |
| MBC Central Limited | Wholesale & retail | 2025 |
| Mbee Consultancy Ltd | Information & communication | 2013 |
| Mbio Limited | Professional & scientific | 2019 |
| MBM Produce Limited | Transport & logistics | 1947 |
| MBM Waffles Limited | Hospitality | 2025 |
| MBN Medical Ltd | Health & social care | 2026 |
| Mbrichardson Consulting Ltd | Professional & scientific | 2023 |
| Mbroker Ltd | Financial services | 2022 |
| MBS Import & Export Co., Ltd | Wholesale & retail | 2025 |
| MBT Block Communication Limited | Information & communication | 2024 |
| MBZ Consulting Limited | Professional & scientific | 2016 |
| MC Cleaning (Herts & Cambs) Limited | Administrative & support | 2014 |
| MC Groundcare Ltd | Administrative & support | 2025 |
| MC Lodges Limited | Hospitality | 2024 |
| MC Research Limited | Information & communication | 1993 |
| MC Residences Ltd | Real estate | 2025 |
| MC Tiling & Interiors Ltd | Construction | 2025 |
| Mc-Avionic Ltd | Manufacturing | 2023 |
| MC8 Solutions Ltd | Information & communication | 2024 |