| MET Haulage Ltd | Transport & logistics | 2025 |
| Metal Craft Holdings Limited | Financial services | 2024 |
| Metal Craft Industries UK Ltd | Manufacturing | 1973 |
| Metal Fabrications (Northampton) Ltd | Professional & scientific | 1998 |
| Meter MIX Holdings Limited | Financial services | 2014 |
| Mexor Trading Limited | Construction | 2011 |
| MEZ Management Ltd | Real estate | 2020 |
| Mfombi Limited | Transport & logistics | 2021 |
| MG Group Estates Limited | Agriculture & fishing | 1974 |
| MG Operations UK Limited | Administrative & support | 2026 |
| MGA Construction Ltd | Construction | 2023 |
| MGE Services (Northants) Ltd | Construction | 2023 |
| MGK Technical Limited | Professional & scientific | 2014 |
| MGL Couriers Ltd | Transport & logistics | 2017 |
| Mgna Trans Ltd | Transport & logistics | 2023 |
| MH Media Group Ltd | Arts & recreation | 2024 |
| Mh&A Healthcare Ltd | Health & social care | 2022 |
| MIA Capital Partners Ltd | Professional & scientific | 2025 |
| Miamildn Luxury Ltd | Wholesale & retail | 2019 |
| Michael Stamper Ltd | Professional & scientific | 2024 |
| Mick George Cladding Ltd | Construction | 2026 |
| Mick's Decorating Services Limited | Construction | 2018 |
| Microdot Ltd | Construction | 2015 |
| Midas Installations Limited | Construction | 2007 |
| Midland Shire Hotels Limited | Hospitality | 2004 |
| Midland Training Services Ltd | Transport & logistics | 2016 |
| Midlands Insulated Conservatory Ltd | Construction | 2019 |
| Midshires Land Surveys Limited | Professional & scientific | 2013 |
| Midshires Property Management Limited | Real estate | 2011 |
| Mig-Tig Hire Limited | Professional & scientific | 1972 |
| Mightygod Property Investment Limited | Real estate | 2025 |
| Mike’S Driving Services Ltd | Transport & logistics | 2024 |
| Milan 88 Ltd | Transport & logistics | 2022 |
| Milani Limited | Financial services | 2022 |
| Milavi Limited | Real estate | 2016 |
| Milesia Ltd | Wholesale & retail | 2017 |
| Milestones Consulting Ltd | Administrative & support | 2013 |
| Militaryyard Ltd | Other services | 2023 |
| Mill Road General Stores Ltd | Hospitality | 2017 |
| Millennium Pizza and Grill Ltd | Hospitality | 2025 |
| Millie's Cafe Limited | Hospitality | 2005 |
| Millward Interim Ltd | Professional & scientific | 2025 |
| Milpet - M Ltd | Transport & logistics | 2014 |
| Mina Care Services Ltd | Administrative & support | 2019 |
| Mind Tree Solutions Ltd | Professional & scientific | 1999 |
| Mindcard Gaming Ltd | Information & communication | 2025 |
| Mindif AI Ltd | Information & communication | 2020 |
| Mini Monkeys Messy Play Ltd | Education | 2024 |
| Minimax Travel Ltd | Administrative & support | 2008 |
| Miniruby Ltd | Wholesale & retail | 2023 |
| Minninnooka Ltd | Agriculture & fishing | 2015 |
| Minninnooka Polo & Riding School Ltd | Education | 2024 |
| Minotaur Systems Limited | Professional & scientific | 2026 |
| Mioo Limited | Health & social care | 2020 |
| Miratom Ltd | Construction | 2016 |
| Mirka Peronska Beauty & Laser Ltd | Other services | 2021 |
| Mirus Interiors Limited | Manufacturing | 2025 |
| MISHA2FASHION Ltd | Wholesale & retail | 2025 |
| Mission Wellbeing C.I.C. | Other services | 2024 |
| Mister Gere Ltd | Information & communication | 2026 |
| Mistral Baits Limited | Other services | 1998 |
| Mita Trans Ltd | Transport & logistics | 2021 |
| Mitaro Ltd | Information & communication | 2014 |
| Mitchell Access Control Systems Limited | Manufacturing | 1997 |
| Mithras Ventures Ltd | Professional & scientific | 2024 |
| MIX Flow Systems Limited | Manufacturing | 2007 |
| Mixed Construction Ltd | Construction | 2025 |
| MJ Tsco Services Limited | Administrative & support | 2010 |
| MJ Bross Ltd | Wholesale & retail | 2020 |
| Mj's Taste and Treats Ltd | Manufacturing | 2026 |
| Mjgbulkservices Limited | Transport & logistics | 2022 |
| MJM Consultants and Business Services Limited | Professional & scientific | 2018 |
| MJM Investments Limited | Real estate | 2019 |
| MJT Comms Limited | Information & communication | 2019 |
| MJT Construction Ltd | Administrative & support | 2025 |
| MK Electronics Ltd | Information & communication | 2001 |
| MK Hydro Dipping Ltd | Construction | 2019 |
| MK Oils Limited | Transport & logistics | 2013 |
| MK Packaging Engineering Ltd | Professional & scientific | 2018 |
| MKH Landscaping Ltd | Construction | 2022 |
| MLA Architecture Limited | Construction | 2017 |
| MLA Land & Development Ltd | Real estate | 2021 |
| Mlnj Ltd | Extraterritorial | 2024 |
| Mmagic Services Ltd | Transport & logistics | 2016 |
| Mmap Pathways CIC | Administrative & support | 2024 |
| MMI Music Management Limited | Arts & recreation | 2012 |
| MMM Property Management Ltd | Real estate | 2022 |
| Mmmlicious Limited | Hospitality | 2015 |
| MMS Technology Ltd | Information & communication | 2023 |
| Mo's Flavour Limited | Hospitality | 2024 |
| Model Estates Ltd | Real estate | 2019 |
| Model Railway Events Limited | Administrative & support | 2025 |
| Model Railway Express Ltd | Extraterritorial | 2015 |
| Model Transport Ltd | Transport & logistics | 2015 |
| Modi Investments Ltd | Hospitality | 2026 |
| Modnvape Ltd | Wholesale & retail | 2023 |
| Moisac Limited | Construction | 2025 |
| Moldman Systems Ltd | Manufacturing | 2014 |
| Momai Limited | Construction | 2009 |
| Momentum Lean Consulting Ltd | Professional & scientific | 2025 |