| Maxwell Swim Club Limited | Arts & recreation | 2016 |
| MAY Hill Drive Management Limited | Real estate | 2021 |
| Maybury Court Freehold Company Limited | Households | 2003 |
| Mayer General Practice Ltd | Health & social care | 2017 |
| Mayflower Lets Limited | Real estate | 2015 |
| Mayge Limited | Households | 2025 |
| MAZ Accountants Ltd | Professional & scientific | 2023 |
| MAZ Administration Ltd | Professional & scientific | 2026 |
| MAZ Landscaping Limited | Construction | 2015 |
| MAZ Lean Consultant Ltd | Professional & scientific | 2023 |
| MAZ UK Investment Ltd | Real estate | 2026 |
| Mazilu Trading Limited | Wholesale & retail | 2025 |
| Mazz Courier Services Ltd | Transport & logistics | 2024 |
| Mazz FM Ltd | Administrative & support | 2023 |
| MB Impex Limited | Wholesale & retail | 2021 |
| MB Medical Care Ltd | Health & social care | 2026 |
| MBA Limited | Extraterritorial | 1976 |
| MBA Technology Solutions Ltd | Extraterritorial | 2022 |
| MBB Projects Limited | Construction | 2026 |
| MBD 2024 Limited | Construction | 2024 |
| Mbhhospitality Ltd | Hospitality | 2025 |
| MBK Housing Ltd | Real estate | 2024 |
| MBW Associates (Dorset) Limited | Professional & scientific | 2003 |
| MC Landfill Solutions Limited | Professional & scientific | 2026 |
| MC Writing Services Limited | Administrative & support | 2014 |
| Mcandrew Associates Limited | Administrative & support | 2008 |
| MCB Transport Limited | Transport & logistics | 2022 |
| Mcclymont Ltd | Health & social care | 2018 |
| Mccombie Partnership Ltd | Professional & scientific | 2018 |
| Mccormack Group Ltd | Wholesale & retail | 2025 |
| Mccormick (Littleborough) Limited | Real estate | 1991 |
| Mccormick Europe Limited | Financial services | 1995 |
| Mccormick Foods (U.K.) Limited | Professional & scientific | 1961 |
| Mccormick International Holdings | Financial services | 2000 |
| Mccormick Merchandising Services Limited | Other services | 2001 |
| Mccoys Wendover Limited | Wholesale & retail | 2014 |
| Mccurley & Hayden Limited | Other services | 2018 |
| MCD Facades Ltd | Construction | 2023 |
| Mcdonald Brickwork 2005 Limited | Administrative & support | 2005 |
| Mcdonald Brickwork Limited | Construction | 1997 |
| Mcdonnell Contracts Limited | Construction | 2010 |
| MCG Surveying Services Limited | Professional & scientific | 2025 |
| Mcgregg Property Limited | Real estate | 2025 |
| Mcgrumpy and Snuffles (Aylesbury) Ltd | Wholesale & retail | 2016 |
| Mcgrumpy and Snuffles Ltd | Wholesale & retail | 2016 |
| Mcintyre Enterprises Ltd | Professional & scientific | 2022 |
| Mcintyre Group Ltd | Financial services | 2024 |
| Mcintyre Property Investments Ltd | Real estate | 2020 |
| Mckenna Properties Limited | Construction | 2006 |
| Mckenzie Ross Services Ltd | Information & communication | 2026 |
| Mckinstery Ltd | Water & waste | 2026 |
| Mclarenbanks Ltd | Professional & scientific | 2019 |
| Mcnaughton Dynamics Limited | Manufacturing | 1987 |
| Mcoys Investments Limited | Real estate | 2024 |
| MCR Property Investment Solutions Ltd | Real estate | 2024 |
| MD Property Corp Ltd | Real estate | 2025 |
| MD Regulatory Consultants Ltd | Professional & scientific | 2022 |
| MD Smart Housing PVT Limited | Real estate | 2022 |
| MD Smart Solutions Limited | Information & communication | 2017 |
| MD Spark Services Ltd | Construction | 2022 |
| Mdat Ltd | Information & communication | 2023 |
| MDB Lubricants Ltd | Professional & scientific | 2023 |
| MDG Global Limited | Manufacturing | 2014 |
| MDG Media Limited | Professional & scientific | 2022 |
| MDH Assets Ltd | Wholesale & retail | 2020 |
| MDJ3 Group Ltd | Education | 2021 |
| MDL 88 Limited | Transport & logistics | 2023 |
| Mdoss Consulting Limited | Information & communication | 2024 |
| MDP Partners Limited | Real estate | 2021 |
| MDW Associates Ltd | Professional & scientific | 2020 |
| Mead Property Construction Ltd | Construction | 2017 |
| Meadow (Aylesbury) Management Company Limited | Households | 1986 |
| Meadowside Residential Care Home Limited | Administrative & support | 2012 |
| Mechanology Ltd | Professional & scientific | 2022 |
| Med-Eq (Europe) Limited | Health & social care | 2011 |
| Medaffairs Solutions Ltd | Professional & scientific | 2023 |
| Medecon Healthcare UK Limited | Wholesale & retail | 2008 |
| Media Bikes Limited | Professional & scientific | 2026 |
| Mediangels Career Solutions Ltd | Administrative & support | 2018 |
| Mediaport Solutions Ltd | Administrative & support | 2005 |
| Medic-Ear Limited | Wholesale & retail | 1993 |
| Medical Tax (UK) Limited | Professional & scientific | 1998 |
| Medikerr Ltd | Health & social care | 2021 |
| Medilink Healthcare Limited | Health & social care | 2020 |
| Medio Tiempo Limited | Wholesale & retail | 2018 |
| Medipulse Training Ltd | Education | 2022 |
| Medisense AI Ltd | Information & communication | 2025 |
| Mednovation Ltd | Other services | 2024 |
| Medscience Group Ltd | Education | 2017 |
| Meducair Consulting Ltd | Professional & scientific | 2022 |
| Mega Petroleum Limited | Wholesale & retail | 2010 |
| Megan Roberts Limited | Health & social care | 2013 |
| Meghna Plaza Ltd | Wholesale & retail | 2025 |
| Mehndi by Chandni Ltd | Arts & recreation | 2025 |
| Mehow Construction Ltd | Construction | 2012 |
| Mehrban Properties Limited | Real estate | 2023 |
| MEL Estates Limited | Real estate | 2016 |
| Mela AM Limited | Hospitality | 2025 |
| Melanie Morton Communications Limited | Professional & scientific | 2012 |
| Meliora Global Management Consultancy Ltd | Professional & scientific | 2023 |