| Milby Meadows LLP | | 2023 |
| Milcombe Homes Ltd | Construction | 2013 |
| Milestone Taxation Consultants Limited | Professional & scientific | 2009 |
| Mili Fiddlers Hamlet Ltd | Arts & recreation | 2021 |
| Millers Granolithic Contractors Limited | Construction | 1997 |
| Millfields (Hall Green) Management Company Limited | Households | 2022 |
| Millharbour Energy Limited | Construction | 2016 |
| Millharbour FM Ltd | Construction | 2016 |
| Millharbour Group Ltd | Construction | 2015 |
| Millharbour MEP Ltd | Construction | 2016 |
| Millharbour Sprinklers Limited | Construction | 2015 |
| Million Dreams Investment Company Limited | Financial services | 2025 |
| Millstar Plant Limited | Administrative & support | 2017 |
| Millwest Construction Ltd | Construction | 2024 |
| Milsons Fintech Ltd | Information & communication | 2018 |
| Milton Johnson Ltd | Households | 2022 |
| Mimi & Flori Ltd | Wholesale & retail | 2024 |
| Mimi Ltd | Hospitality | 2023 |
| Mindas Building Services Ltd | Construction | 2017 |
| Mindful Mindset Ltd | Administrative & support | 2012 |
| Mindlogics Ltd | Professional & scientific | 2013 |
| Mindset Health Ltd | Professional & scientific | 2023 |
| Minella Weddings Ltd | Extraterritorial | 2022 |
| Mini Peas Ltd | Arts & recreation | 2022 |
| Mink Consulting Limited | Professional & scientific | 2004 |
| Minstral Management Limited | Professional & scientific | 2012 |
| Mint Beauty Ltd | Other services | 2019 |
| Mint Properties (London) Limited | Hospitality | 2004 |
| Minted Group Ltd | Financial services | 2025 |
| Miracle Homes Limited | Construction | 2018 |
| Mission Community Ltd | Professional & scientific | 2022 |
| Mistr. (Borehamwood) Limited | Wholesale & retail | 2020 |
| Mistr. Holdings Limited | Wholesale & retail | 2020 |
| Mitch Haul Ltd | Transport & logistics | 2023 |
| Mitchell Investments Ltd | Real estate | 2024 |
| Mitchell Stephenson Holdings Limited | Financial services | 2024 |
| Mitchell Stephenson Limited | Administrative & support | 2001 |
| Mitho Energy Limited | Manufacturing | 2026 |
| Mitigateops Ltd | Information & communication | 2026 |
| Mivida Wealth Limited | Professional & scientific | 2017 |
| Mizu CM Limited | Hospitality | 2025 |
| MJ Deed Installations Ltd | Construction | 2019 |
| MJ Results Group Limited | Professional & scientific | 2020 |
| MJ Results Limited | Extraterritorial | 2024 |
| MJ Venture Group Ltd | Real estate | 2025 |
| MJB Build Ltd | Construction | 2017 |
| MJB Venture Ltd | Real estate | 2017 |
| MJD Consultancy Services Limited | Professional & scientific | 2016 |
| MJD Electrical Limited | Construction | 2013 |
| MJG London Limited | Construction | 2017 |
| MJH Mortgage Services Limited | Financial services | 2014 |
| Mjhd Homes Ltd | Real estate | 2026 |
| MJS Financial Planning Ltd | Professional & scientific | 2021 |
| MJW Promotions Ltd | Arts & recreation | 2018 |
| MK Digital Notebook Limited | Professional & scientific | 2025 |
| MK Electritech Limited | Construction | 2025 |
| MK Grooming Ltd | Other services | 2025 |
| MKB Accountancy Limited | Professional & scientific | 1999 |
| MKB Property Limited | Real estate | 2018 |
| MKD Plumbing Ltd | Construction | 2019 |
| MKP Admin Limited | Information & communication | 1996 |
| MKT Sourcing Limited | Financial services | 2009 |
| MLD Home Support Services Ltd | Administrative & support | 2023 |
| MLG Designs Ltd | Professional & scientific | 2023 |
| MLM Fitness Ltd | Wholesale & retail | 2025 |
| Mlrtech Limited | Information & communication | 2025 |
| MLS International Holdings Ltd | Real estate | 2023 |
| MM Dental and Aesthetics Limited | Health & social care | 2025 |
| MM Nistrean Limited | Construction | 2024 |
| Mmam Properties Ltd | Real estate | 2023 |
| Mmch Ltd | Administrative & support | 2012 |
| MMM Culture Consultants Ltd | Professional & scientific | 2018 |
| Mmshi Consulting Limited | Financial services | 2015 |
| MNS Trading Ltd | Wholesale & retail | 2017 |
| MNV Property Ltd | Real estate | 2019 |
| Mo-Sys Engineering Limited | Manufacturing | 2012 |
| Mo-Sys Holding Ltd | Financial services | 2019 |
| Mo-Yan Engineering Services Ltd | Professional & scientific | 2019 |
| Moat Farm Management Company Limited | Households | 2021 |
| Moat House Farm Ltd | Administrative & support | 2024 |
| Mobility Guys Capital Ltd | Professional & scientific | 2023 |
| Mode Management Ltd | Administrative & support | 2016 |
| Model Catering Limited | Hospitality | 2019 |
| Modern Connect Limited | Other services | 2021 |
| Modeset Limited | | 1987 |
| Modus Partnerships Limited | Construction | 2019 |
| Moimpex Ltd | Wholesale & retail | 2026 |
| MON AMI Andy Limited | Administrative & support | 2010 |
| Moneymaking Industries Limited | Extraterritorial | 2010 |
| Monolux Worktops Ltd | Manufacturing | 2026 |
| Montana Polo Ltd | Arts & recreation | 2005 |
| Montcalder Holdings Limited | Professional & scientific | 2026 |
| Montglass Ltd | Construction | 2022 |
| Montpellier Resourcing Ltd | Administrative & support | 2010 |
| Montra Service Limited | Other services | 2024 |
| Moody International (Holdings) Limited | Administrative & support | 2003 |
| Moody Residential Holdings Ltd | Real estate | 2022 |
| Moonstays Ltd | Real estate | 2024 |
| Moonstone Property Investments Limited | Real estate | 2016 |
| Moore Flooring Limited | Construction | 2022 |