| MK Real Estate Limited | Real estate | 1999 |
| MKA1919 Limited | Wholesale & retail | 2018 |
| MLH Property Management Limited | Real estate | 2021 |
| Mnemosyne Limited | Extraterritorial | 2023 |
| MO & Mack Building and Electrical Ltd | Construction | 2026 |
| Mobile Munch UK Ltd | Wholesale & retail | 2020 |
| Mobile Ultrasound Limited | Health & social care | 2003 |
| Modern Landscapes and Driveways Ltd | Administrative & support | 2026 |
| Modifire Safety Ltd | Construction | 2017 |
| Moizy Ltd | Transport & logistics | 2025 |
| Mojo Clinical Ltd | Health & social care | 2019 |
| Mojo Residential Ltd | Real estate | 2022 |
| Moka Pharmaceuticals Limited | Wholesale & retail | 1998 |
| Moldsteel Limited | Real estate | 1980 |
| Molow Ltd | Information & communication | 2024 |
| Moltglow Limited | | 1977 |
| Moment Vision Construction Ltd | Construction | 2025 |
| Momentum Commodities Ltd | Wholesale & retail | 2020 |
| Momentvfx Limited | Professional & scientific | 2017 |
| Monc Design Ltd | Wholesale & retail | 2019 |
| Mondo Consulting Limited | Professional & scientific | 2005 |
| Mondolat Zindre Ltd | Hospitality | 2025 |
| Mondrich Limited | Information & communication | 2011 |
| Monitor Recruitment Limited | Extraterritorial | 2008 |
| Monolabs Ltd | Information & communication | 2016 |
| Monophonic Production Limited | Information & communication | 2013 |
| Montpelier Group Limited | Financial services | 2026 |
| Montreux Financial Ltd | Financial services | 2016 |
| Monty Ventures Limited | Information & communication | 2026 |
| Moodplus Ltd | Wholesale & retail | 2024 |
| Moore 23 Ltd | Arts & recreation | 2026 |
| Moorhouse Training Limited | Administrative & support | 2018 |
| More and More Ltd | Hospitality | 2021 |
| Moreton Joinery Ltd | Manufacturing | 2024 |
| Morgan AVN Ltd | Professional & scientific | 1983 |
| Morgan Langley Limited | Information & communication | 2005 |
| Morgan-Kostov Keys Ltd | Wholesale & retail | 2019 |
| Moritech Robot Technologies UK Ltd | Manufacturing | 2024 |
| Morroccansweeney Ltd | Other services | 2018 |
| Mother Apothecary Limited | Wholesale & retail | 2022 |
| Mothers Pride Limited | Information & communication | 2021 |
| Motimation Ltd | Information & communication | 2022 |
| Moto Retro Ltd | Wholesale & retail | 2023 |
| Mouseback Limited | Professional & scientific | 2011 |
| Mouv Limited | Other services | 2022 |
| Move Gym LDN Ltd | Arts & recreation | 2025 |
| Move Ontime Ltd | Transport & logistics | 2024 |
| Move Physio Ltd | Health & social care | 2018 |
| Movingheads Limited | Wholesale & retail | 2024 |
| MP Accountancy Support Limited | Administrative & support | 2025 |
| MPL Property Limited | Real estate | 2014 |
| MR Darcy’S Doggy Day Care and Services Ltd | Other services | 2025 |
| MR Singh Local Store Ltd | Wholesale & retail | 2018 |
| MS Greek Food Trading Ltd | Hospitality | 2026 |
| MSD IT Consulting Limited | Professional & scientific | 2024 |
| Mske Property LLP | | 2025 |
| Mske Property Management Ltd | Extraterritorial | 2025 |
| MT UK Solicitors Limited | Professional & scientific | 2017 |
| MTN Music Limited | Information & communication | 2013 |
| Mtvh Foundation Limited | Real estate | 2023 |
| Mugabi Limited | Health & social care | 2015 |
| Muj's Spice Fusion Limited | Hospitality | 2025 |
| Muja Construction Ltd | Construction | 2024 |
| Mukund Technologies Limited | Information & communication | 2013 |
| Mulberry Contracts Limited | | 1981 |
| Muller Consulting Ltd | Information & communication | 2023 |
| Multigroup Ltd | Construction | 2018 |
| Muralhas Mediterranean Ltd | Hospitality | 2025 |
| Murphy Clark Design Ltd | Information & communication | 2021 |
| Muse Hair Studio Ltd | Other services | 2025 |
| Museum Properties Limited | Real estate | 2017 |
| Muskaan Pizza Limited | Hospitality | 2026 |
| Musso Limited | Administrative & support | 2014 |
| Mutimer P & C Limited | Real estate | 2015 |
| Mwcr Limited | Administrative & support | 2025 |
| MX Group Ltd | Wholesale & retail | 2021 |
| My Brazilian Doctor Telemedicine Ltd | Professional & scientific | 2026 |
| My Courses Ltd | Information & communication | 2016 |
| My Day Method Ltd | Education | 2026 |
| My Gadgets Ltd | Wholesale & retail | 2024 |
| My Gadgets Retail Limited | Other services | 2026 |
| My Market Consumer Limited | Professional & scientific | 2013 |
| My Next ME Ltd | Information & communication | 2017 |
| My Services Limited | Professional & scientific | 2018 |
| Mydayout Limited | Information & communication | 2025 |
| Myelin Technologies Limited | Administrative & support | 2022 |
| Myhomey Property Ltd | Real estate | 2025 |
| Myhylian Limited | Wholesale & retail | 2025 |
| MYPROPERTY247 Limited | Real estate | 2024 |
| Mystery JAM Ltd | Arts & recreation | 2021 |
| Mystery Jets Live Limited | Arts & recreation | 2003 |
| Màzo London Ltd | Wholesale & retail | 2019 |
| N & D Launderette (Borehamwood) Ltd | Other services | 2024 |
| N Ozgul Accountancy Ltd | Professional & scientific | 2017 |
| N S Nternational Ltd | Real estate | 2024 |
| N-D Property Investments Limited | Real estate | 2018 |
| NA Cleaning Services Ltd | Administrative & support | 2019 |
| Naas Properties GB Limited | Real estate | 2024 |
| Nabigeta Ltd | Information & communication | 2019 |
| Nadeemone Ltd | Real estate | 2022 |