| M & P Finishes Limited | Construction | 2022 |
| M a M Project Consultants Limited | Professional & scientific | 2010 |
| M Associates Limited | Administrative & support | 2025 |
| M Barnes Contracts Ltd | Construction | 2017 |
| M Bennett Consulting Ltd | Professional & scientific | 2019 |
| M C Carpentry & Construction Services Limited | Construction | 2019 |
| M C Consulting South East Ltd | Professional & scientific | 2026 |
| M G Farriery Limited | Agriculture & fishing | 2008 |
| M I Consultancy Limited | Administrative & support | 2015 |
| M J Curtis Limited | Construction | 2014 |
| M J Wood Limited | Real estate | 1976 |
| M Kalsi T/A Aquila Ltd | Wholesale & retail | 2026 |
| M Leftwich Ltd | Construction | 2017 |
| M R Mortgage Services Limited | Financial services | 2023 |
| M&L Comms Limited | Information & communication | 2014 |
| M&R Property Rentals Ltd | Real estate | 2021 |
| M.A.N Assets Limited | Extraterritorial | 2013 |
| M.B.F Plumbing and Property Maintenance Ltd | Construction | 2026 |
| M.D. Collings Limited | Other services | 2014 |
| M.J.W.P. Ltd | Construction | 2004 |
| M.T. Mitchell Limited | Construction | 2014 |
| M.Y Collective Co Limited | Hospitality | 2025 |
| M.Z. Lofts Ltd | Construction | 2016 |
| M4 Production Music Library Limited | Information & communication | 2019 |
| M6 Recovery Services Ltd | Transport & logistics | 2021 |
| Ma-Maison Home & Garden Limited | Wholesale & retail | 2023 |
| Mabel Property Investments Ltd | Real estate | 2026 |
| MAC Trading 66 Ltd | Wholesale & retail | 2021 |
| Macanna Ltd | Professional & scientific | 2025 |
| Macclesfield House Limited | Real estate | 2025 |
| Macfinn Limited | Professional & scientific | 2013 |
| Mach 1 Sales Ltd | Wholesale & retail | 2021 |
| Machina Data Ltd | Information & communication | 2025 |
| Mackay Events Ltd | Professional & scientific | 2023 |
| Macleanj Limited | Health & social care | 2018 |
| Maddox Constructions Ltd | Construction | 2016 |
| Made From the Heart Limited | Arts & recreation | 2012 |
| Madena Consulting Ltd | Financial services | 2025 |
| Magdalene Farms Limited | Construction | 2016 |
| Magix UK Limited | Wholesale & retail | 2019 |
| Magma Coatings Ltd | Construction | 2025 |
| Mahalasa Ltd | Health & social care | 2009 |
| Maimor Company Limited | Extraterritorial | 2020 |
| Maintain IT Systems Ltd | Information & communication | 2012 |
| Majestic Motor Homes Ltd | Wholesale & retail | 2017 |
| Make Waves Music Ltd | Professional & scientific | 2026 |
| Malby Architects Ltd | Professional & scientific | 2009 |
| Maldon Thermal Ltd | Construction | 2021 |
| Malika Holdings Limited | Administrative & support | 2017 |
| Malo Hair Limited | Other services | 2008 |
| Malyon Executive Search Limited | Administrative & support | 2019 |
| MAN Like Robbie Ltd | Information & communication | 2017 |
| Mandeng Associates Limited | Professional & scientific | 2021 |
| Mandy Oakley Designs Limited | Wholesale & retail | 2015 |
| MANGO-5 Contract Services Limited | Professional & scientific | 2012 |
| MANGO-5 Management Ltd | Professional & scientific | 2017 |
| Manor Farm Stables Developments Ltd | Construction | 2022 |
| Mansard Building Services Limited | Administrative & support | 1996 |
| Mansard Limited | Administrative & support | 1996 |
| Manta RAY Property Limited | Real estate | 2025 |
| Manyi Health Ltd | Health & social care | 2019 |
| Manymarketingsolutions Ltd | Professional & scientific | 2025 |
| Mapledean Works Management Limited | Professional & scientific | 2007 |
| Maplestead Land Limited | Real estate | 2026 |
| Maralexa Services Ltd | Other services | 2015 |
| Marbill Investments Limited | Financial services | 2020 |
| Marchlink Limited | Construction | 1993 |
| Margolis Limited | Extraterritorial | 2012 |
| Margot Properties Ltd | Real estate | 2024 |
| Marian's Holdings Limited | Administrative & support | 2017 |
| Marina Filippelli Limited | Hospitality | 2012 |
| Marine Services Transport Boat Charters Limited | Manufacturing | 2022 |
| Mark MAY Limited | Information & communication | 2020 |
| Mark Parker Rail Limited | Administrative & support | 2015 |
| Mark Readings Limited | Professional & scientific | 2020 |
| Mark Rudderham Consulting Ltd | Professional & scientific | 2018 |
| Marq Andrews Limited | Wholesale & retail | 2012 |
| Martinos Catering Limited | Wholesale & retail | 2016 |
| Marts & Sparks Ltd | Construction | 2016 |
| Marwood Services Ltd | Construction | 2019 |
| Masc Construction Ltd | Construction | 2016 |
| MASON59 Holdings Limited | Households | 2020 |
| Master the Game Ltd | Education | 2024 |
| Masters @ Work Roofing Ltd | Construction | 2024 |
| Masters of Corruption Ltd | Professional & scientific | 2022 |
| Matt James Properties Limited | Real estate | 2022 |
| Mayer Building Services Ltd | Construction | 2017 |
| Mayer Property Solutions Ltd | Real estate | 2018 |
| Mayfair Plumbing and Drainage Ltd | Water & waste | 2024 |
| Mayflower Decor Ltd | Construction | 2019 |
| Mayflower Healthcare Alliance Ltd. | Health & social care | 2011 |
| Mayflower High School | Education | 2011 |
| Mayflower IT Limited | Construction | 2010 |
| Maytree Design Limited | Professional & scientific | 2013 |
| MB Gardens Limited | Administrative & support | 2017 |
| MBA Business Consultancy Services Limited | Information & communication | 2011 |
| MBG Companies Ltd | Other services | 2020 |
| MC Construction Management Ltd | Construction | 2026 |
| Mcallister Electrical Services Limited | Construction | 2015 |
| Mccarthy Oldham Business Developments Limited | Information & communication | 2017 |