| MON35 Limited | Hospitality | 2017 |
| Monarch Building Solutions Ltd | Construction | 2018 |
| Monarch Energy Ltd | Energy | 2022 |
| Monazite Consulting Limited | Wholesale & retail | 2026 |
| Mondelez UK Finance Company Limited | Professional & scientific | 2016 |
| Mondelez UK Holdings & Services Limited | Manufacturing | 1897 |
| Mondelez UK Limited | Administrative & support | 1925 |
| Monetrix Consulting Limited | Professional & scientific | 2025 |
| Money Makes Money Limited | Wholesale & retail | 2020 |
| Monika Anton Associates Limited | Professional & scientific | 2016 |
| Monks & Maberly Limited | Manufacturing | 1979 |
| Monodose Ltd | Manufacturing | 2025 |
| Monsei Group Ltd | Professional & scientific | 2025 |
| Montage Homes Ltd | Manufacturing | 2025 |
| Montagu Saxby Limited | Real estate | 1952 |
| Montecristo (London) Limited | Households | 2024 |
| Montford Brothers & Co Ltd | Construction | 2026 |
| Montrex Global Limited | Wholesale & retail | 2026 |
| Monument Professional Solutions Limited | Professional & scientific | 2017 |
| Monumental Gardens Ltd | Administrative & support | 2022 |
| Monverogroup Ltd | Wholesale & retail | 2026 |
| Moonlight Textile and Clothing Ltd | Wholesale & retail | 2022 |
| Moonlight Unique Limited | Other services | 2025 |
| Moonwake Apparel Ltd | Wholesale & retail | 2025 |
| Moor Online Ltd | Wholesale & retail | 2025 |
| Moore Lighting Limited | Arts & recreation | 2014 |
| Moosavia Ltd | Wholesale & retail | 2025 |
| Mopidevi Group Ltd | Wholesale & retail | 2025 |
| Morasco Limited | Real estate | 1972 |
| Morcom Woodley Developments Limited | Construction | 2015 |
| Morcom Woodley Holdings Limited | Financial services | 2009 |
| Morearc Limited | Real estate | 2000 |
| Morent Ltd | Real estate | 2023 |
| Morgan Interiors Ltd | Construction | 2016 |
| Morgan Lifting Company Limited | Construction | 2016 |
| Moribus Estates Limited | Financial services | 2021 |
| Morii Events Ltd | Hospitality | 2024 |
| Morning View Capital Limited | Construction | 2022 |
| Moroty Limited | Hospitality | 2007 |
| Mortified Racing Limited | Wholesale & retail | 2021 |
| Moseley Business Holdings Ltd | Financial services | 2024 |
| Mostera Limited | Real estate | 2025 |
| Motla Enterprises Limited | Professional & scientific | 2026 |
| Motor 2 Go Limited | Wholesale & retail | 2014 |
| Motor Icon Limited | Wholesale & retail | 2022 |
| Motorcycle Madness Ltd | Wholesale & retail | 2024 |
| Motorcycle Transporter Limited | Wholesale & retail | 2025 |
| Mount Apollo Rentals Ltd | Real estate | 2024 |
| Mount Copper Properties Ltd | Real estate | 2026 |
| Mountbatten House Management Company Limited | Households | 2025 |
| Mountk Properties Limited | Real estate | 2021 |
| Mouslum Tea London Ltd | Wholesale & retail | 2025 |
| MOVE37 Capital Limited | Professional & scientific | 2023 |
| MOVE37 Capital Management LLP | | 2023 |
| Moventis Logistics Limited | Real estate | 2017 |
| Moviola Media Limited | Professional & scientific | 2020 |
| Moxcha Ltd | Wholesale & retail | 2020 |
| MPA Architecture Limited | Administrative & support | 2006 |
| MPM Technologies Limited | Other services | 2004 |
| MQS Designs Ltd | Professional & scientific | 2018 |
| MR B Contractors 1 Ltd | Construction | 2019 |
| MR Eddy's Barber Shop Ltd | Other services | 2020 |
| MR John Burrows Ltd | Extraterritorial | 2023 |
| MR Shawarma London Ltd | Hospitality | 2026 |
| MR. M EGG Ltd | Hospitality | 2023 |
| Mrcgp London Ltd | Education | 2019 |
| Mrees Consulting Ltd | Information & communication | 2025 |
| MRG (Denham) Holdings Limited | Financial services | 2025 |
| MS & RK Properties Ltd | Real estate | 2006 |
| MS Builder Construction Ltd | Manufacturing | 2025 |
| MS Carriers Ltd | Transport & logistics | 2017 |
| MS Construction (London) Ltd | Construction | 2022 |
| MS Fruit and VEG Limited | Wholesale & retail | 2015 |
| MS Joinery London Ltd | Manufacturing | 2015 |
| MS Mower Ltd | Professional & scientific | 2013 |
| MS Property London Ltd | Real estate | 2021 |
| MS Truck Services Ltd | Wholesale & retail | 2026 |
| MSC Cruise Management (UK) Limited | Transport & logistics | 2014 |
| MSH Consulting Ltd | Information & communication | 2026 |
| Msingi Group Ltd | Professional & scientific | 2025 |
| MSL Connections Ltd | Administrative & support | 2024 |
| Msma Ltd | Professional & scientific | 2025 |
| MSP Corporation Ltd | Wholesale & retail | 2024 |
| MSP Real Estate Investments Limited | Real estate | 2025 |
| MSP Research Academy Ltd | Professional & scientific | 2024 |
| MSR IT Ltd | Information & communication | 2003 |
| Msrj Ltd | Wholesale & retail | 2019 |
| MT Smart Tiling Ltd | Construction | 2019 |
| MTD Spreadsheet Limited | Information & communication | 2018 |
| MTG Property Investment Venture Ltd | Real estate | 2020 |
| MTG Venture Holdings Ltd | Financial services | 2026 |
| MTG Venture Ltd | Construction | 2010 |
| MTM Houses Limited | Real estate | 2025 |
| MTT Scientific Editing Ltd | Information & communication | 2013 |
| Mubrbirken Coffee Limited | Hospitality | 2023 |
| Mubrchester Coffee Limited | Hospitality | 2023 |
| Mubrtelford Coffee Ltd | Hospitality | 2025 |
| Mudan Building Contractors Ltd | Construction | 2014 |
| Mudu International Management Consultancy Limited | Professional & scientific | 2008 |
| Muka Brickwork Ltd | Construction | 2022 |