| Millbrook Building Solutions Ltd | Construction | 2010 |
| Millennium Environmental Services Ltd | Professional & scientific | 2022 |
| Miller & Curtis Ltd | Construction | 2022 |
| Miller Property Lettings Ltd | Real estate | 2019 |
| Millgate & Harris Homes Ltd | Real estate | 2023 |
| Millgate and Harris Ltd | Manufacturing | 2023 |
| Millwood Products Ltd | Wholesale & retail | 2013 |
| Milly's Nursery School Limited | Education | 2016 |
| Milon Distrib Ltd | Transport & logistics | 2026 |
| Milsec Limited | Information & communication | 2017 |
| Mimi & Misek Ltd | Real estate | 2022 |
| Mina Nail Huong D Nguyen Ltd | Other services | 2022 |
| Mindbodyconnect Limited | Information & communication | 2023 |
| Mindful Expeditions Ltd | Administrative & support | 2024 |
| Mindful Footsteps CIC | Other services | 2025 |
| Mindle Holdings Limited | Administrative & support | 2022 |
| Mindset Sport CIC | Wholesale & retail | 2021 |
| Mindspace Foundation CIC | Other services | 2019 |
| Mindspace Therapy-Studio Limited | Health & social care | 2018 |
| Mindstrade Ltd | Wholesale & retail | 2023 |
| Mindzone Media Ltd | Health & social care | 2019 |
| Minerva Digital Solutions Limited | Information & communication | 2014 |
| Minerva Talking Therapies Ltd | Health & social care | 2023 |
| Minitec UK Limited | Manufacturing | 2005 |
| Minster Court Management Company Limited | Real estate | 1997 |
| MIP Logistic Ltd | Transport & logistics | 2019 |
| Mira-Ivo Limited | Health & social care | 2020 |
| Mirai International Ltd | Wholesale & retail | 2024 |
| Miranova House Limited | Information & communication | 2026 |
| Miriyala Assets Management Limited | Financial services | 2021 |
| Misam Ltd | Transport & logistics | 2024 |
| Misholt Properties Limited | Real estate | 2006 |
| Miso Creative Ltd | Professional & scientific | 2018 |
| Miss Aneta Polish Food Ltd | Wholesale & retail | 2015 |
| Mission Control Consultancy Limited | Wholesale & retail | 1998 |
| Mitford Fulham LLP | | 2007 |
| Mito Properties Limited | Construction | 2004 |
| MJ Dooley (Dental Surgeon) Limited | Health & social care | 2009 |
| MJ Facility Plus Limited | Administrative & support | 2019 |
| MJ Robinson Properties Limited | Real estate | 2016 |
| MJB Bathrooms Ltd | Construction | 2021 |
| Mjec Resource Limited | Administrative & support | 2019 |
| MJG Planning Limited | Professional & scientific | 2025 |
| MJR Copy and Content Ltd | Information & communication | 2016 |
| MJT Photo Limited | Professional & scientific | 2021 |
| MJT Video Limited | Information & communication | 2026 |
| MK Link Services Limited | Health & social care | 2015 |
| MK Wojtas Limited | Administrative & support | 2021 |
| MKA Basingstoke Ltd | Real estate | 2024 |
| Mkey Houses Ltd | Construction | 2020 |
| MLB Innovation Ltd | Manufacturing | 2019 |
| Mlcr Ltd | Real estate | 2025 |
| MLE Tax and Accounting Ltd | Professional & scientific | 2013 |
| Mleaccounting Ltd | Professional & scientific | 2008 |
| MLM Trans Ltd | Transport & logistics | 2023 |
| MLS Data Limited | Information & communication | 2017 |
| MLT Consultants Group Limited | Information & communication | 2026 |
| MM Fuel Group Ltd | Wholesale & retail | 2025 |
| MM1 Filling Stations Ltd | Wholesale & retail | 2020 |
| MM2 Filling Stations Ltd | Wholesale & retail | 2020 |
| MM3 Filling Stations Ltd | Wholesale & retail | 2020 |
| Mmarinus Properties Ltd | Real estate | 2023 |
| MMB Construction and Decoration Ltd | Construction | 2015 |
| MMW Properties Limited | Real estate | 2017 |
| Mobile Development Limited | Information & communication | 2014 |
| Mobile Masters (London) Limited | Wholesale & retail | 2009 |
| Mobilenous Limited | Information & communication | 2013 |
| Mobrage Ltd | Wholesale & retail | 2021 |
| Mochi Property Group Ltd | Construction | 2026 |
| Mockleford Limited | Financial services | 2020 |
| MOD Showjumpers Limited | Agriculture & fishing | 2026 |
| Modern Moulds Associates Limited | Manufacturing | 1988 |
| Modern Moulds Limited | Manufacturing | 1983 |
| MOF Empire Ltd | Hospitality | 2025 |
| Mogs Logistics Ltd | Transport & logistics | 2020 |
| Mojolak Properties Ltd | Real estate | 2016 |
| Molin Limited | Construction | 2009 |
| Molver Developments Limited | Construction | 2025 |
| Monick Ltd | Health & social care | 2019 |
| Monks Financial Services Ltd | Professional & scientific | 2013 |
| Monkton Ltd | Professional & scientific | 2022 |
| Monolith SEO Limited | Information & communication | 2014 |
| Mont Holdings Limited | Real estate | 2025 |
| Montrose Kelly Ltd | Administrative & support | 2009 |
| Moo-Moo Belle Vintage Ice Cream Company Limited | Hospitality | 2015 |
| Moon Communications Ltd | Professional & scientific | 2019 |
| Moongazy Publishing Ltd | Information & communication | 2007 |
| Moongrey Ltd | Real estate | 2022 |
| Moore SSJ Land Limited | Households | 2021 |
| Mooreco Italy Limited | Administrative & support | 2021 |
| Mooreco Limited | Administrative & support | 2018 |
| Moorelands Limited | Wholesale & retail | 2008 |
| Mooshmedia Marketing Ltd | Professional & scientific | 2007 |
| Moraira Property Limited | Hospitality | 2009 |
| Morestead Solutions Limited | Information & communication | 2024 |
| Morgan Plumbing Limited | Construction | 2019 |
| Morng Solutions Ltd | Professional & scientific | 2011 |
| Morris Ashby Limited | Construction | 2006 |
| Morris Gordon Engineering Ltd | Extraterritorial | 2020 |
| Mortimer Cars Ltd | Wholesale & retail | 2020 |