| Matsuba Ltd | Other services | 2024 |
| Matthew Grant Hairdressing Ltd | Other services | 2018 |
| Matthews Environmental Services Limited | Water & waste | 2021 |
| Mave (UK) Ltd | Real estate | 2013 |
| Maverick Pubs and Restaurants Ltd | Hospitality | 2013 |
| Maverish Ltd | Professional & scientific | 2013 |
| MAW Commercial Cleaning and Maintenance Ltd | Households | 2026 |
| MAX Capital Management Limited | Administrative & support | 2018 |
| Maxi Freshco Ltd | Wholesale & retail | 2020 |
| Maxi-Press DRM Ltd | Wholesale & retail | 2025 |
| Maxrefix Ltd | Wholesale & retail | 2025 |
| Maxtom Ltd | Professional & scientific | 2007 |
| Maxwells Property Services Limited | Real estate | 2022 |
| Maxx Tech Limited | Wholesale & retail | 2023 |
| Maya MAY Limited | Wholesale & retail | 2024 |
| Mayan Hairdressing Limited | Other services | 2017 |
| Mayco UK Ltd | Professional & scientific | 2017 |
| Maydim's Ltd | Administrative & support | 2025 |
| Mayfair Hotels Ltd | Hospitality | 2022 |
| Mayflower Education Consultants Ltd | Education | 2011 |
| Mayfly Investments Limited | Real estate | 2011 |
| MB Cleanworks Limited | Administrative & support | 2025 |
| MC Car Sales Ltd | Wholesale & retail | 2023 |
| MC Sports and Social C.I.C. | Hospitality | 2026 |
| Mccc Limited | Financial services | 2017 |
| Mcchall Investments Limited | Administrative & support | 2019 |
| Mccombes I.T. Consultancy Limited | Information & communication | 2010 |
| Mccreary Investments Ltd | Financial services | 2026 |
| Mcgettigans Holdings Limited | Financial services | 2025 |
| Mcghie's Plumbing & Heating Limited | Construction | 2016 |
| MCJ International Ltd | Professional & scientific | 2022 |
| Mcleans Private Ltd | Health & social care | 2017 |
| MCM (Oundle) Ltd | Construction | 2022 |
| Mcmanus Executive Development Ltd | Professional & scientific | 2024 |
| Mcmillan Hayward Limited | Professional & scientific | 1999 |
| Mcneill's Fine Food and Rose Industries Limited | Manufacturing | 1983 |
| Mcpa Software Limited | Information & communication | 2003 |
| Mcrobieadams Limited | Financial services | 2016 |
| Mcvier Ltd | Real estate | 2023 |
| MD Healthcare Professionals Ltd | Health & social care | 2026 |
| MDF Mouldings Limited | Administrative & support | 2016 |
| MDF Store Holdings Limited | Administrative & support | 2022 |
| MDF Store Limited | Manufacturing | 2014 |
| MDN Collective Limited | Information & communication | 2019 |
| Me-Fix Auto Ltd | Wholesale & retail | 2024 |
| Meaas Ltd. | Information & communication | 2007 |
| Mead Associates Limited | Real estate | 1993 |
| Mead Farm Trading Limited | Agriculture & fishing | 2019 |
| Meadow and Bay Limited | Administrative & support | 2021 |
| Meadow View (Arncott) Management Company Limited | Households | 2020 |
| Meaningful Lives Limited | Health & social care | 2015 |
| Meatology Limited | Hospitality | 2012 |
| Medibridge Healthtech Ltd | Manufacturing | 2025 |
| Medic Assist International | Health & social care | 2003 |
| Medical Writing Solutions Ltd | Professional & scientific | 2023 |
| Medkab Unique Fashion Ltd | Wholesale & retail | 2026 |
| Meet & Greet Security Limited | Administrative & support | 2024 |
| Mega Merchandise Limited | Professional & scientific | 2020 |
| Mega Nutrition Ltd | Wholesale & retail | 2017 |
| Mega Tyre Store Buckingham Limited | Wholesale & retail | 2017 |
| Mega Tyre Store Limited | Wholesale & retail | 2007 |
| Megastruct Ltd | Construction | 2025 |
| Megha UK Limited | Wholesale & retail | 2003 |
| Megsrus Ltd | Wholesale & retail | 2025 |
| Meikle Farming Limited | Agriculture & fishing | 2015 |
| Meilleure Décor Ltd | Wholesale & retail | 2025 |
| Meliora Technologies Ltd | Administrative & support | 2022 |
| Melody in Mind Ltd | Health & social care | 2018 |
| Melodys VR Ltd | Extraterritorial | 2021 |
| Menagerie Investments Limited | Financial services | 2018 |
| Mental Mastery Ltd | Education | 2023 |
| Menura Limited | Wholesale & retail | 2026 |
| Mercross (Electrical) Limited | Wholesale & retail | 1972 |
| Mercury Expedia Ltd | Transport & logistics | 2018 |
| Merivale Design Group Ltd | Professional & scientific | 2019 |
| Merritt Tate Ltd | Other services | 2023 |
| Merrygorounduk Limited | Wholesale & retail | 2018 |
| Merson Enterprises Ltd | Information & communication | 2016 |
| Merton Street (Banbury) Management Company Limited | Real estate | 1988 |
| Metag UK Limited | Financial services | 2019 |
| Mettex Electric Company Limited | Manufacturing | 1973 |
| Meyler Coaching Limited | Professional & scientific | 2004 |
| Meztek Ltd | Information & communication | 2020 |
| MF Enterprises Limited | Financial services | 1999 |
| MGL Ventures Limited | Extraterritorial | 2012 |
| MH Growth Limited | Information & communication | 2025 |
| MH Rentals Ltd | Real estate | 2017 |
| MHI ENG Ltd | Professional & scientific | 2014 |
| MI8 Holdings Ltd | Financial services | 2025 |
| Michael Housley Associates Limited | Professional & scientific | 2016 |
| Michael W.W. Kidd Limited | Professional & scientific | 2006 |
| Michco 1701 | Financial services | 2017 |
| Michelle Wood Design Ltd | Administrative & support | 2012 |
| Mick Mckenna Limited | Administrative & support | 2015 |
| Mid-England Barrow Ltd | Other services | 2018 |
| Midas Kitchens & Bathrooms Ltd | Wholesale & retail | 2023 |
| Midas Light Films Limited | Information & communication | 2013 |
| Midas Property Ltd | Construction | 2015 |
| Middle Aston Ltd | Construction | 2018 |
| Middlehurst Consulting Limited | Professional & scientific | 2026 |