| Montandon Holdings Limited | Financial services | 2025 |
| Moonlight Partnership Limited | Professional & scientific | 2023 |
| Moore's Estates (EP) Ltd | Real estate | 2021 |
| Moore’S Group Limited | Financial services | 2022 |
| Moorings Close Management Company Ltd | Households | 2026 |
| Moortown Capital LLP | | 2002 |
| Mora Oxford Ltd | Construction | 2023 |
| More Homes DFC Ltd | Construction | 2021 |
| Moresurefdn C.I.C. | Education | 2020 |
| Moreton Dental Limited | Health & social care | 2023 |
| Morgan and Carver Property Services Limited | Real estate | 2026 |
| Morgan Bentley Consultants Limited | Professional & scientific | 2020 |
| Morgan Oxford Education Limited | Education | 2013 |
| Morgan Oxford Limited | Construction | 2003 |
| Morild Holdings Limited | Real estate | 2021 |
| Moritz Capital Limited | Professional & scientific | 2025 |
| Morley's Property Limited | Real estate | 2024 |
| Morphotech Limited | Information & communication | 2018 |
| Morrell Avenue Services Ltd | Administrative & support | 2022 |
| Morrell Grounds Ltd | Real estate | 2021 |
| Morris Builders (Aylesbury) Limited | Financial services | 1954 |
| Morris Cleaners Limited | Administrative & support | 2003 |
| Mortgage Advance Limited | Financial services | 1997 |
| Mortgages Inc. Ltd | Financial services | 2004 |
| Mortimer & MAY Consulting Ltd | Professional & scientific | 2018 |
| Mortimer Fields Management Company Limited | Households | 2018 |
| Mortons Limited | Hospitality | 1989 |
| Mosaic Contour Grinders Limited | Manufacturing | 2003 |
| Moshi Limited | Health & social care | 2013 |
| Mosiac Consulting Ltd | Information & communication | 2026 |
| Moss Number One Limited | Wholesale & retail | 1966 |
| Mossinator Ltd | Administrative & support | 2021 |
| Mothers 4 Justice Ubuntu CIC | Education | 2025 |
| Motion Vehicle Solutions Limited | Administrative & support | 2026 |
| Motive Fuels Limited | Wholesale & retail | 2021 |
| Motive Technologies Ltd | Professional & scientific | 2013 |
| Moto Cycle Ltd | Wholesale & retail | 2020 |
| Motorspotting Ltd | Wholesale & retail | 2024 |
| Motrium Ltd | Information & communication | 2020 |
| Mouldlife Limited | Wholesale & retail | 2004 |
| Mount Prosupport Services Ltd | Health & social care | 2022 |
| Mountain Horse UK Limited | Wholesale & retail | 2015 |
| MOUNTS2GO Limited | Manufacturing | 2011 |
| Mountstuart Limited | Construction | 2015 |
| Mouse News Letter Limited | Professional & scientific | 1987 |
| Mouthguards Direct Limited | Professional & scientific | 1993 |
| Move Design Ltd | Professional & scientific | 2016 |
| Move IT MAX Limited | Transport & logistics | 2017 |
| Moving Maps Ltd. | Information & communication | 2017 |
| Moving Picture Travel Ltd | Administrative & support | 2017 |
| Moving Target Films Ltd | Information & communication | 2012 |
| Movo Projects Ltd | Professional & scientific | 2012 |
| MOX Consultants Limited | Professional & scientific | 2017 |
| Moxham Basham Interior Design Limited | Professional & scientific | 2021 |
| Mozaik Technology Ventures Limited | Administrative & support | 1992 |
| MP VIP Services Ltd | Wholesale & retail | 2023 |
| MPN Plumbing & Heating Services Limited | Construction | 2013 |
| MQF Corporate Services Limited | Professional & scientific | 2002 |
| MR Fulfillers Limited | Wholesale & retail | 2025 |
| MR LAI Limited | Real estate | 2025 |
| MR Watson's Cafe Limited | Hospitality | 2022 |
| MR. 8 Ball Ltd | Arts & recreation | 2026 |
| MR. Light Limited | Wholesale & retail | 2012 |
| MRC Management Ltd | Hospitality | 2024 |
| MRF Solutions Limited | Real estate | 2014 |
| MRF Window Cleaning Services Limited | Administrative & support | 2016 |
| MRM (Oxford) Limited | Real estate | 2022 |
| MS Embedded Ltd | Information & communication | 2022 |
| MS Interiors & Design Limited | Professional & scientific | 2004 |
| MS JJJ Limited | Health & social care | 2020 |
| MSA Education & Consultancy Ltd | Professional & scientific | 2023 |
| Msampa Mining Ltd | Mining & quarrying | 2016 |
| MSK Decorating Limited | Construction | 2023 |
| Msquared Holdings Limited | Real estate | 2019 |
| Msquared Oxford Limited | Real estate | 2021 |
| MT Promedt Consulting Ltd | Professional & scientific | 2020 |
| Mtdb Ltd | Information & communication | 2017 |
| MTN Consultants Limited | Administrative & support | 1998 |
| Mtreeyne Ltd | Wholesale & retail | 2025 |
| MUBEENMAZHAR87 Ltd | Wholesale & retail | 2026 |
| Mugwump.Net Ltd | Information & communication | 2024 |
| Muhammad Salman Ltd | Other services | 2025 |
| Muji & Son’S Ltd | Wholesale & retail | 2018 |
| Mujtaba & Salman Ltd | Hospitality | 2020 |
| Mukja Ltd | Hospitality | 2023 |
| Mulberry House Oxford Management Company Ltd | Real estate | 2024 |
| Mullender's Limited | Education | 2014 |
| Multilingua Consulting Limited | Information & communication | 2025 |
| Multimodality Medicines Limited | Professional & scientific | 2021 |
| Mums the Word Nanny Agency Limited | Other services | 2009 |
| Mundus Pro Ltd | Real estate | 2025 |
| Munteanu IT Ltd | Information & communication | 2025 |
| Muox Microwave Technologies Ltd | Professional & scientific | 2026 |
| Muoxmt Ltd | Professional & scientific | 2025 |
| Murphy Hospitality Ltd | Hospitality | 2023 |
| Murray Asset Management UK Limited | Financial services | 2015 |
| Murray Asset Nominees UK Limited | Extraterritorial | 2014 |
| Murrez Holdings Ltd | Financial services | 2023 |
| Murrumba Limited | Financial services | 2025 |
| Musaco Limited | Wholesale & retail | 2025 |