| Maple Engineering Services Limited | Professional & scientific | 2013 |
| Maple Wood Property Ltd | Real estate | 2020 |
| Maplestone Property Services Ltd | Administrative & support | 2025 |
| Mare SOC. Limited | Administrative & support | 2025 |
| Marek Medical Limited | Health & social care | 2024 |
| Marion Lyons Interiors Ltd | Professional & scientific | 2021 |
| Marius & Raluca Ltd | Transport & logistics | 2026 |
| Mark Ayres Holdings Limited | Real estate | 2024 |
| Mark Boscott Golf Ltd | Wholesale & retail | 2017 |
| Mark Jarrett Commercials Ltd | Wholesale & retail | 2022 |
| Mark Saunders Construction Ltd | Construction | 2015 |
| Market Corner JX Ltd | Hospitality | 2025 |
| Market Inn Expert Ltd | Administrative & support | 2019 |
| Market Square Media Limited | Professional & scientific | 1998 |
| Marketing Inside Limited | Administrative & support | 2003 |
| Marlow Developments Ltd | Construction | 2015 |
| Marquiss LA Masion Limited | Real estate | 2025 |
| Martar Consulting Limited | Wholesale & retail | 2013 |
| Martin NYE Limited | Professional & scientific | 2012 |
| Martin NYE Probate Limited | Professional & scientific | 2020 |
| Marvel Accounting Limited | Professional & scientific | 2018 |
| Marzipan Pigs Ltd | Real estate | 2020 |
| Massage Matters LLP | | 2022 |
| Matador Company Limited(The) | Manufacturing | 1984 |
| Matt Ottaway Contracting Ltd | Public administration | 2023 |
| Matter of Form Ltd | Information & communication | 2010 |
| Matthew Turnbull Limited | Financial services | 1946 |
| Maverick Europe Limited | Construction | 1998 |
| Mavush Ltd | Agriculture & fishing | 2023 |
| MAW Artist Ltd | Professional & scientific | 2023 |
| Mayes HR Consultancy Limited | Administrative & support | 2020 |
| MB Associates Limited | Professional & scientific | 2007 |
| MCJ Solutions Limited | Professional & scientific | 2020 |
| Mcmr Limited | Construction | 2012 |
| Meadbee Ltd | Manufacturing | 2024 |
| Meadow View Landscapes Ltd | Administrative & support | 2013 |
| Medi Investments Ltd | Real estate | 2023 |
| Medical Property Management Limited | Construction | 2016 |
| Medilend Limited | Extraterritorial | 2016 |
| Meera&M Limited | Information & communication | 2016 |
| Mega Caff Limited | Hospitality | 2017 |
| Megatrend Solutions Ltd | Information & communication | 2023 |
| Melbourne Luce Limited | Professional & scientific | 2018 |
| MEM Roofing Contracts Ltd | Construction | 2026 |
| Mendex Trading Limited | Other services | 2022 |
| Meridian Interiors Limited | Construction | 2001 |
| Meritaas Ltd | Professional & scientific | 2023 |
| Messygirl Ltd | Information & communication | 2024 |
| Metarisk Ltd | Professional & scientific | 2019 |
| Mevetec Ltd | Real estate | 2017 |
| MEY Buckingham Ltd | Hospitality | 2024 |
| Mhnewman Ltd | Other services | 2022 |
| MHS Landscapes Limited | Administrative & support | 2015 |
| Miccio Limited | Wholesale & retail | 2025 |
| Michael Anthony (Leighton Buzzard) Lettings Ltd | Real estate | 2023 |
| Michael Anthony (Leighton Buzzard) Ltd | Real estate | 2023 |
| Michael Anthony Lettings Ltd | Real estate | 2022 |
| Michael J O'Brien Carpet & Vinyl Fitter Ltd | Construction | 2018 |
| Michael Simon Property Limited | Real estate | 2025 |
| Micona (UK) Limited | Construction | 1974 |
| Microcopy (Midlands) Limited | Administrative & support | 2005 |
| Microcopy Systems Limited | Administrative & support | 2000 |
| Microgrid Developments Ltd | Professional & scientific | 2020 |
| Midon Properties Limited | Real estate | 1967 |
| Midwinter Property Developments Ltd | Real estate | 2014 |
| MIHAELA777 Ltd | Extraterritorial | 2012 |
| MIL Power Limited | Manufacturing | 1998 |
| Milestone Sustainability Limited | Professional & scientific | 2026 |
| Mill Close (Winslow) Management Co Ltd | Professional & scientific | 2005 |
| Milton Keynes Crescent Cricket Club CIC | Education | 2024 |
| Mindkind Families CIC | Education | 2026 |
| Miraiia Limited | Manufacturing | 2026 |
| MJ Land Ltd | Construction | 2024 |
| MJH Imports Ltd | Transport & logistics | 2026 |
| MJS Consultancy Ltd | Professional & scientific | 2021 |
| MK Business Support Services Ltd | Professional & scientific | 2022 |
| MK Cottage Limited | Hospitality | 2024 |
| MK18 Hub Ltd | Wholesale & retail | 2025 |
| MK18 Limited | Professional & scientific | 2018 |
| MK2 Computing Ltd | Other services | 2014 |
| MK2 Repair Limited | Other services | 2020 |
| MKC Vocational Training Ltd | Education | 2012 |
| Mkmation Limited | Professional & scientific | 2025 |
| Mkoss Limited | Wholesale & retail | 2002 |
| MM3 Design Limited | Professional & scientific | 2003 |
| MO Estates and Holdings Ltd | Real estate | 2026 |
| Mobile Kneadz Ltd | Other services | 2025 |
| Mobilere Ltd | Information & communication | 2012 |
| Modulas Woodworking Ltd | Professional & scientific | 2018 |
| Moev Ltd | Professional & scientific | 2021 |
| MOF Holdings Limited | Information & communication | 2018 |
| MOH Properties Limited | Real estate | 1994 |
| Mohammed Shoib Consultancy Ltd | Other services | 2025 |
| Monkombe Farm Management Company Limited | Real estate | 2020 |
| Monode Limited | Manufacturing | 1978 |
| Montague Pianos Limited | Administrative & support | 1997 |
| Montpellier Walk Interior Limited | Professional & scientific | 2024 |
| Moorhouse & Co. Ltd | Manufacturing | 2024 |
| Moorland Fisheries Limited | Arts & recreation | 2003 |
| More Joy Limited | Wholesale & retail | 2023 |