| Medimab Biotherapeutics Ltd | Professional & scientific | 2020 |
| Medis Health Limited | Wholesale & retail | 2011 |
| Medyagalaxy Ltd | Wholesale & retail | 2025 |
| Meecon Ltd | Professional & scientific | 2022 |
| Megan Nicholls Ltd | Information & communication | 2023 |
| Megla Limited | Professional & scientific | 2014 |
| Melfort Estates Limited | Extraterritorial | 2015 |
| Menaz UK Limited | Administrative & support | 2025 |
| Mental Health Natters CIC | Education | 2022 |
| Meon View Estates Limited | Real estate | 2000 |
| Mera Social Payment Ltd | Wholesale & retail | 2026 |
| Mercavia Ltd | Wholesale & retail | 2025 |
| Merlin a V Limited | Construction | 2023 |
| Merralls Motors Ltd | Wholesale & retail | 2022 |
| Mescla Limited | Arts & recreation | 2012 |
| Messy Church Limited | Extraterritorial | 2012 |
| Metaltest UK Limited | Professional & scientific | 2016 |
| Metro United Properties Limited | Real estate | 2024 |
| Metweld Sheet Metal & Laser Limited | Manufacturing | 2023 |
| MEWS86 Limited | Households | 2013 |
| Mezzeh House Ltd | Hospitality | 2015 |
| MF Decorating Oxford Limited | Construction | 2018 |
| MF Newco Limited | Real estate | 2023 |
| MFB Properties Oxford Ltd | Construction | 2025 |
| MFM Design Limited | Professional & scientific | 2023 |
| MFV Healthcare & Consulting (UK) Ltd | Health & social care | 1998 |
| Mgryaz Limited | Other services | 2026 |
| MH Holdings Transport UK Limited | Professional & scientific | 2006 |
| MHB Intellectual Property Holdings Limited | Extraterritorial | 2015 |
| Mhbg Management Limited | Real estate | 2002 |
| Mhlsales Ltd | Wholesale & retail | 2023 |
| MHT Forwarding Limited | Extraterritorial | 2019 |
| MI20 Ltd | Wholesale & retail | 2022 |
| Michael a Jennings Associates Limited | Administrative & support | 2002 |
| Michael Flakes Limited | Information & communication | 2020 |
| Michaelsson Contractors Limited | Construction | 2011 |
| Michel Hurel Transport U.K. Limited | Transport & logistics | 1986 |
| Mick Foden Commercials Ltd | Wholesale & retail | 2021 |
| Microlife Health Management Limited | Wholesale & retail | 2002 |
| Microview Limited | Information & communication | 2026 |
| Miebach Consulting Limited | Professional & scientific | 2017 |
| Miele Company Limited | Wholesale & retail | 1963 |
| Mike Hampshire Ltd | Wholesale & retail | 2003 |
| Mikko's Cleaning Limited | Administrative & support | 2022 |
| Miles Away Touring Limited | Arts & recreation | 2012 |
| Miles D. Webster Limited | Professional & scientific | 2010 |
| Milestone Education Services Limited | Administrative & support | 2016 |
| Milini Ltd | Real estate | 2024 |
| Millhill Tools Limited | Extraterritorial | 1973 |
| Millport Transport Ltd | Transport & logistics | 2017 |
| Millyday Limited | Information & communication | 2016 |
| Milton Branch Ltd | Transport & logistics | 2018 |
| Milton Garden Machinery Ltd | Other services | 2019 |
| Milton Heights Residents Limited | Real estate | 1992 |
| Milton Keynes Mobility Limited | Wholesale & retail | 2003 |
| Milton Road (Sutton Courtenay) Management Company Limited | Households | 2014 |
| Mimio Labs Limited | Information & communication | 2025 |
| Ministeps Ltd | Education | 2019 |
| Minotaur Synergies Ltd | Professional & scientific | 2015 |
| Mirai Bidco Limited | Financial services | 2023 |
| Mirai Holdco Limited | Financial services | 2023 |
| Mirai Midco Limited | Financial services | 2023 |
| Mirhox Global Ltd | Professional & scientific | 2025 |
| Mirmar Design and Construction Limited | Construction | 2019 |
| Miroslaw Bielecki Transport Ltd | Transport & logistics | 2022 |
| Mirror Free LLP | | 2022 |
| Mison & Mison Limited | Administrative & support | 2018 |
| Mission Integrated Systems Limited | Extraterritorial | 2001 |
| Mission: Purple Ltd | Professional & scientific | 2026 |
| Mitchpixx Ltd | Information & communication | 2006 |
| Mitochondria Limited | Real estate | 2024 |
| Miu’S Beauty Limited | Other services | 2017 |
| MIX 14 IP Limited | Administrative & support | 2018 |
| MIX 14 Ltd | Manufacturing | 2013 |
| MJ Beauty and Brows Ltd | Other services | 2026 |
| MJ Car Valet Detailing Ltd | Other services | 2022 |
| MJ Motor Repairs Ltd | Wholesale & retail | 2024 |
| MJM Distribution Ltd | Wholesale & retail | 2022 |
| MK Autos Servicing and Repairs Limited | Wholesale & retail | 2023 |
| MK Rigs Limited | Wholesale & retail | 2025 |
| Modern Living Homes Limited | Construction | 2017 |
| Mododuo Limited | Information & communication | 2017 |
| Modus Coaching & Events Limited | Professional & scientific | 2019 |
| Molecule 2 Medicine Limited | Professional & scientific | 2022 |
| Molly Bloom Limited | Information & communication | 2023 |
| Moloney Sporthorses Ltd | Agriculture & fishing | 2024 |
| Molyneux Dental Limited | Health & social care | 2017 |
| Monaghan Mechanical Ltd | Construction | 2026 |
| Moneywise Wealth Management Limited | Financial services | 2002 |
| Monkhouse Architect Ltd | Professional & scientific | 2018 |
| Monti&Me Limited | Wholesale & retail | 2024 |
| Moodbros Ltd | Arts & recreation | 2024 |
| Moon Dream Photography Ltd | Professional & scientific | 2022 |
| Moon-Age Engineering Limited | Manufacturing | 2011 |
| Moonlight Publishing Limited | Information & communication | 1980 |
| Moony LL Limited | Manufacturing | 2022 |
| Mootle UK Limited | Arts & recreation | 2023 |
| Moretex Ltd | Transport & logistics | 2022 |
| Moreton Building & Construction Ltd | Construction | 2018 |
| Morijo Properties Limited | Real estate | 2022 |