| Miller Fluid Heads (Europe) Limited | Wholesale & retail | 1998 |
| Millers Close (Walton-On-Thames) Management Company Limited | Households | 2011 |
| Millfield (Hungerford) Management Company Limited | Households | 1986 |
| Millfield Property Investments Limited | Professional & scientific | 1941 |
| Millgate Court Management Company Limited | Households | 1988 |
| Mind Body Touch Training Ltd | Wholesale & retail | 2023 |
| Mind Body Wild Ltd | Information & communication | 2019 |
| Mint Performance Ltd | Professional & scientific | 2008 |
| Miradorus Ltd | Professional & scientific | 2011 |
| Miratech Europe Limited | Other services | 2012 |
| Mirror Originals Limited | Wholesale & retail | 2022 |
| Miscellanea Hotels and Leisure Limited | Hospitality | 1994 |
| Mitchell Back Office Support Ltd | Professional & scientific | 2022 |
| Mjeaton Property Limited | Real estate | 2023 |
| MJF & Associates Ltd | Professional & scientific | 2019 |
| MJH Architects Limited | Professional & scientific | 2020 |
| MJI Foods Limited | Hospitality | 2014 |
| MJL73 Limited | Financial services | 2018 |
| Mjma Consulting Limited | Information & communication | 2005 |
| MJP Plumbing & Heating Limited | Construction | 2006 |
| MJR Builders Ltd | Construction | 2022 |
| MJS Landscapes Limited | Administrative & support | 2025 |
| MK Admiral Ltd | Construction | 2025 |
| MK Builders PVT Ltd | Construction | 2026 |
| MK7 Construction Ltd | Construction | 2026 |
| MKL South Limited | Financial services | 2022 |
| Mkvn Business Support Services Ltd | Professional & scientific | 2024 |
| ML Solutions Limited | Other services | 2016 |
| MLH Financial Services Limited | Professional & scientific | 2013 |
| MLS Construction Team Limited | Construction | 2026 |
| MMO Amber Consultancy Limited | Professional & scientific | 2011 |
| Mmpi Manufacturing Limited | Manufacturing | 2014 |
| MNH Associates Limited | Professional & scientific | 2014 |
| MNH Traders Limited | Hospitality | 2025 |
| Model "T" Ford Register(The) | Other services | 1986 |
| Modern International Group Ltd | Wholesale & retail | 2026 |
| Modus Laboratories Limited | Professional & scientific | 2009 |
| Moid Law Ltd | Professional & scientific | 2022 |
| Moissanite Couture Ltd | Manufacturing | 2024 |
| Mojo I.T. Limited | Information & communication | 2003 |
| Mojo Inc Ltd | Professional & scientific | 2019 |
| Molan Consulting Limited | Professional & scientific | 2018 |
| Molecular Medical Ltd | Professional & scientific | 2021 |
| Momentum Sports Ltd | Arts & recreation | 2000 |
| Monaghan Mews Ltd | Real estate | 2022 |
| Money to Go Ltd | Professional & scientific | 2004 |
| Moniss Limited | Extraterritorial | 2003 |
| Monkhaven Ltd | Manufacturing | 2016 |
| Monkwell Associates Limited | Professional & scientific | 2025 |
| Monkwell Investments Limited | Real estate | 2025 |
| Montagu Land Limited | Real estate | 1991 |
| Monteagle Construction Ltd | Construction | 2024 |
| Montgomery Court Residents Limited | Households | 2014 |
| Monty Pope Ltd | Real estate | 2025 |
| Mooncoin Solutions Limited | Professional & scientific | 2026 |
| Moonlight Ridge Stables Ltd | Agriculture & fishing | 2015 |
| Moor Park House Estate Management Limited | Real estate | 2015 |
| Moorcroft Associates Ltd | Professional & scientific | 2008 |
| Moore Sparks Electrical Limited | Construction | 2022 |
| Moorlands Close Management Company Limited | Households | 2008 |
| Mooskin Limited | Wholesale & retail | 2021 |
| Moovies Limited | Professional & scientific | 2013 |
| Mopod Limited | Manufacturing | 2014 |
| Moran Roofing Specialists Limited | Construction | 2012 |
| Morbrooke Developments Ltd | Real estate | 2012 |
| Morbrooke Ltd | Real estate | 2012 |
| Morchard Bishop Limited | Extraterritorial | 2003 |
| Moremango Ltd | Administrative & support | 2022 |
| Morgan Wright Precision Engineering Limited | Manufacturing | 1997 |
| Morganti Golf Limited | Arts & recreation | 2014 |
| Morris & Welford UK Ltd | Extraterritorial | 2011 |
| Morse Labs Limited | Information & communication | 2020 |
| Morton Thomas Consulting Limited | Professional & scientific | 2017 |
| Mortonsfield Limited | Professional & scientific | 2016 |
| Morvelle Ltd | Manufacturing | 2025 |
| Mossa Studios Limited | Arts & recreation | 2009 |
| Mothership Software Limited | Information & communication | 2010 |
| Motional Ltd | Information & communication | 2015 |
| Motivated Results Limited | Administrative & support | 2014 |
| Motor Action 360 Ltd | Manufacturing | 2026 |
| Motorhomeco Ltd | Professional & scientific | 2023 |
| Mount Pleasant (Kidlington) Residents Management Company Limited | Households | 2021 |
| Mountain Top Holdings Ltd | Financial services | 2018 |
| Movedin Limited | Construction | 2018 |
| Movies to Go Ltd | Professional & scientific | 2004 |
| Moxcorp Limited | Professional & scientific | 2024 |
| Moxion Limited | Professional & scientific | 2025 |
| MPR Technology Limited | Information & communication | 1996 |
| MR a W Davidson Ltd | Health & social care | 2012 |
| MR BEN Maintenance Limited | Construction | 2023 |
| MR Gray Branding Ltd | Information & communication | 2017 |
| MR Homemaster Limited | Construction | 2017 |
| MR Scan Limited | Professional & scientific | 2008 |
| MRC Capital Ltd | Real estate | 2019 |
| MRD Associates Ltd | Financial services | 2019 |
| MRH Walmsley Ltd | Information & communication | 2013 |
| MRJ Investment Consultants Limited | Professional & scientific | 2014 |
| MS Mayfair Property Limited | Real estate | 2023 |
| MS Prestige Cars Ltd | Transport & logistics | 2024 |
| MS Rentals Limited | Arts & recreation | 2019 |