| Mentmore Park Farms Limited | Agriculture & fishing | 1991 |
| Mentmore Properties Ltd | Real estate | 2024 |
| Merantus Ltd | Administrative & support | 2017 |
| Mercypoint Ltd | Wholesale & retail | 2024 |
| Mere Court Management Limited | Households | 1999 |
| Merit Order Advisory Ltd | Professional & scientific | 2026 |
| Meritics Limited | Professional & scientific | 2006 |
| Merrison Commercial Ltd | Wholesale & retail | 2025 |
| Merrygomind Limited | Arts & recreation | 2023 |
| Metadata Consultants Ltd | Information & communication | 2023 |
| Metanoia Leadership Ltd | Professional & scientific | 2017 |
| Meteor Spark Ltd | Information & communication | 2025 |
| Metime Property Ltd | Real estate | 2018 |
| Metro Court Residents Management Company Limited | Households | 2006 |
| Mfgc Limited | Administrative & support | 2024 |
| MG Distribution Ltd | Wholesale & retail | 2023 |
| MG Elite Ltd | Real estate | 2025 |
| MG Motorsport Limited | Wholesale & retail | 2012 |
| MG Step Forward Ltd | Health & social care | 2026 |
| MGA Manufacturing Limited | Manufacturing | 2022 |
| MGR IT Consulting Ltd | Information & communication | 2019 |
| MH Cater Ltd | Hospitality | 2024 |
| Mh&G Limited | Wholesale & retail | 2023 |
| Miami Logistics Ltd | Transport & logistics | 2015 |
| Miami Property Management Ltd | Real estate | 2026 |
| Michael Boyce Limited | Wholesale & retail | 2011 |
| Michael Wellesley Young Limited | Information & communication | 2023 |
| Michael Wilkes Consulting Limited | Administrative & support | 2009 |
| Mick Box Limited | Other services | 2015 |
| Micklefield Road (High Wycombe) Management Company Limited | Real estate | 1985 |
| Microbetter Limited | | 1987 |
| Microken Limited | Information & communication | 2022 |
| Midsummer Place (LB) Management Limited | Households | 2004 |
| Mikal Healthcare Ltd | Health & social care | 2024 |
| Mikiyama Consulting Ltd | Professional & scientific | 2022 |
| Milestone Management Company (Ledgers Road) Limited | Households | 2016 |
| Milestones Holdings Ltd | Professional & scientific | 2021 |
| Millau Business Limited | Professional & scientific | 2015 |
| Millers Building Services Ltd | Construction | 2017 |
| Millers Consultancy (Land and Development Solutions) Limited | Real estate | 2015 |
| Milliners Court Management Company (St.Albans) Limited | Households | 1998 |
| Milliners Place Management Company Limited | Households | 2010 |
| Milpip Consulting Limited | Information & communication | 2023 |
| Milton Business Consultancy Limited | Professional & scientific | 2008 |
| Milton Keynes Land Limited | Professional & scientific | 2014 |
| Milton Keynes Sailing Club Limited | Arts & recreation | 2001 |
| Milton Keynes Transport Consultancy Limited | Transport & logistics | 2009 |
| Milton Keynes Veterinary Properties Limited | Real estate | 2001 |
| Mimic Business Suite Ltd | Real estate | 2023 |
| Mimic Gifts Ltd | Wholesale & retail | 2021 |
| Mind and Body Collective Ltd | Arts & recreation | 2026 |
| Mind's EYE Associates Limited | Professional & scientific | 2000 |
| Mini Clipper Limited | Transport & logistics | 1987 |
| Mini Clipper Property Limited | Real estate | 2012 |
| Mint PEA Ltd | Professional & scientific | 2024 |
| Mintys Marketplace Ltd | Wholesale & retail | 2026 |
| Miss Magpie Fashion SPY Limited | Other services | 2011 |
| Misticbiz Limited | Administrative & support | 2003 |
| Mitch Mitchell Estate Ltd | Information & communication | 2021 |
| Miter Data Consulting Ltd | Information & communication | 2026 |
| Mitre Court (Freehold) Limited | Households | 2005 |
| Mitre Court Management Limited | Households | 1989 |
| Miyla Apartments Freehold Limited | Households | 2022 |
| MJ LIM Consulting Limited | Information & communication | 2024 |
| MJ Wine Cellars Limited | Wholesale & retail | 2019 |
| MJA Consulting Limited | Professional & scientific | 2024 |
| MJG Internal Controls Ltd | Professional & scientific | 2026 |
| MJM Accountancy Limited | Professional & scientific | 2019 |
| MJS Maintenance Ltd | Other services | 2010 |
| Mjsb Consulting Ltd | Professional & scientific | 2014 |
| MJW Bookkeeping & Accountancy Services Limited | Professional & scientific | 2012 |
| MK Cooling Limited | Construction | 2018 |
| MK Feet Limited | Extraterritorial | 2019 |
| MK Feet Podiatry Clinic Limited | Health & social care | 2019 |
| MK Prestige Carz Ltd | Wholesale & retail | 2026 |
| MK Shotokan Karate Academy Limited | Arts & recreation | 2025 |
| ML Leisure Limited | Administrative & support | 2016 |
| MLC Consults Ltd | Information & communication | 2025 |
| Mlotshwa Healthcare Services Ltd | Health & social care | 2013 |
| MM Forktrucks Ltd | Manufacturing | 2019 |
| MM II Limited | Financial services | 2013 |
| MMV WS Ltd | Manufacturing | 2014 |
| MNJ Windows Ltd | Construction | 2021 |
| Mobile Solutions (AY) Limited | Other services | 2019 |
| MODE24 Collective Ltd | Information & communication | 2024 |
| Modular Engine Limited | Information & communication | 2023 |
| Mojo Design & Animation Studio Limited | Professional & scientific | 2012 |
| Momentum Sports Analytics Ltd | Arts & recreation | 2019 |
| Momentus Music Limited | Information & communication | 1985 |
| Momo Interiors Limited | Wholesale & retail | 2021 |
| Mondaysquares Ltd | Professional & scientific | 2021 |
| Mondego Consulting Ltd | Information & communication | 2022 |
| Montpelier Projects Ltd | Extraterritorial | 2015 |
| Moodles Limited | Information & communication | 2007 |
| Moore Business Consulting Services Limited | Professional & scientific | 2015 |
| Moorhen Court Residents Limited | Households | 1993 |
| Mopping Mommas Limited | Households | 2025 |
| Mora Rentals Ltd | Administrative & support | 2025 |
| Moralle Electronics Limited | Manufacturing | 2012 |
| Mordey Property Consulting Limited | Real estate | 2021 |