| MA Abingdon Ltd | Hospitality | 2022 |
| Maan's FIX & Maintenance Services Ltd | Construction | 2025 |
| Maankulu Food & Wine (UK) Ltd | Wholesale & retail | 2015 |
| MAB Management Limited | Administrative & support | 2006 |
| MAB Partners LLP | | 2003 |
| Mabik Fabrication Ltd | Construction | 2025 |
| Mabus Consultancy Limited | Professional & scientific | 2011 |
| MAC Fisheries Atlantic Fish Cubes Limited | Hospitality | 2021 |
| MAC Traffic Solutions Limited | Other services | 2021 |
| MAC UK Logistics Limited | Transport & logistics | 2015 |
| Macauley Vehicle Solutions Limited | Wholesale & retail | 2018 |
| Macbon Consulting Ltd | Professional & scientific | 2023 |
| Maciej Contractors Ltd | Administrative & support | 2017 |
| Mackenzie HR Limited | Extraterritorial | 2024 |
| Mackenzie Stuart Consulting Ltd | Professional & scientific | 2026 |
| Maddison Ball Creative Ltd | Arts & recreation | 2024 |
| Madge Security Systems Ltd | Administrative & support | 2025 |
| Madison Management Services Ltd | Hospitality | 2017 |
| Madley Ltd | Real estate | 2018 |
| Madraí Reatha Ltd | Information & communication | 2022 |
| Maejam Ltd | Financial services | 2025 |
| Magee Equine Ltd | Agriculture & fishing | 2020 |
| Magnolia Homes Limited | Construction | 2017 |
| Magpie IP Limited | Professional & scientific | 2026 |
| Magpie Windows Ltd | Construction | 2019 |
| Maha's Studio Ltd | Wholesale & retail | 2023 |
| Mahood Tutoring Services Ltd. | Education | 2018 |
| MAJ Fresh VEG Ltd | Wholesale & retail | 2024 |
| Make the Breakthrough Ltd | Professional & scientific | 2021 |
| Maker Unleashed Limited | Information & communication | 2025 |
| Making Families Count C.I.C. | Other services | 2019 |
| Manandtruck Ltd | Transport & logistics | 2024 |
| Manchester MET IC Limited | Education | 2023 |
| Manntec Limited | Professional & scientific | 2008 |
| Manor Farms (Steventon) Limited | Agriculture & fishing | 2005 |
| Mansbridge & Murray Development Limited | Construction | 2014 |
| Mansbridge Developments (UK) Limited | Construction | 2012 |
| Mansbridge Homes Ltd | Construction | 2018 |
| Manus Homes Limited | Real estate | 2026 |
| Manuto Ltd | Construction | 2022 |
| Marcham Community Group | Other services | 2010 |
| Marcham Community Trading Ltd | Administrative & support | 2021 |
| Marcham Road (Abingdon) Limited | Administrative & support | 1972 |
| Marco Polo Oxford Limited | Education | 2008 |
| Marek Uryga Trans Ltd | Transport & logistics | 2018 |
| Mark Burdett Coaching and Consultancy Limited | Professional & scientific | 2024 |
| Mark Humphris Refrigeration & Air Conditioning Limited | Construction | 2009 |
| Mark O'Hara Financial Limited | Financial services | 2005 |
| Market Square Analytics Ltd | Professional & scientific | 2011 |
| Market Town Properties Limited | Real estate | 2021 |
| Marquand Properties Limited | Real estate | 2020 |
| Marron Group UK Holdings Limited | Financial services | 2019 |
| Marsaxlokk Capital Ltd | Financial services | 2024 |
| Marshnet Services Limited | Administrative & support | 2025 |
| Martin Gilbert Motor Repairs Limited | Wholesale & retail | 1987 |
| Marton Construction Ltd | Construction | 2023 |
| Maryam Properties (Oxfordshire) Ltd | Real estate | 2024 |
| Marynczak Limited | Construction | 2026 |
| MAS Electronics (UK) Limited | Manufacturing | 1999 |
| Masonberry Limited | Financial services | 1998 |
| Massey Construction Ltd | Construction | 2012 |
| Master Cleaning Oxford Ltd | Other services | 2021 |
| Master Thatching Limited | Construction | 2014 |
| Matoke Pharma Limited | Other services | 2018 |
| Matrix Arts Centre | Education | 1992 |
| Maus Yazilim Ltd | Wholesale & retail | 2024 |
| Maxed OUT Training Limited | Other services | 2026 |
| Max’S Meat Limited | Agriculture & fishing | 2026 |
| MAY Lease Group Limited | Other services | 2025 |
| Maybree Clinic Limited | Health & social care | 2023 |
| Mayotts Road Flats Management Limited | Administrative & support | 1977 |
| Mays Properties Limited | Real estate | 2004 |
| Mayzee International Limited | Arts & recreation | 2025 |
| Mazdi Ltd | Wholesale & retail | 2025 |
| MC Electrical Services (Long Wittenham) Limited | Construction | 2018 |
| MCA Travel Ltd | Administrative & support | 2020 |
| Mcadden Productions LLP | | 2026 |
| Mcalbyrne Limited | Information & communication | 2025 |
| Mcdonald Farm Services Limited | Agriculture & fishing | 2011 |
| Mcerturk Ltd | Administrative & support | 2024 |
| Mchugh & Mchugh Limited | Real estate | 2012 |
| Mcintyre Heating Services Limited | Construction | 2022 |
| MCJ Living Ltd | Real estate | 2020 |
| Mckenzie Repairs Ltd | Wholesale & retail | 2021 |
| Mclarty Languages Limited | Education | 2002 |
| Mclernon Equine Limited | Agriculture & fishing | 2024 |
| Mcnn Consulting Ltd | Information & communication | 2011 |
| MCS & JS Heritage Limited | Construction | 2003 |
| MCS NOW Limited | Administrative & support | 2023 |
| Mcsh Construction Limited | Construction | 2006 |
| MD & NP Services Ltd | Administrative & support | 2012 |
| MD Dntl Excellence Limited | Financial services | 2024 |
| MDB Bioconsulting Ltd | Professional & scientific | 2025 |
| MDH Construction Ltd | Construction | 2024 |
| MDK Suho Limited | Wholesale & retail | 2021 |
| ME and That MAN Limited | Other services | 2017 |
| Medallion (Design and Build) Limited | Construction | 2019 |
| Medcaptain UK Limited | Financial services | 2021 |
| Medco Solutions Ltd | Manufacturing | 2020 |
| Medilink Logistics Ltd | Transport & logistics | 2026 |