| Martlett House Management Company Limited | Households | 2019 |
| Massimo Health Limited | Health & social care | 2024 |
| Matt Riggall Carpentry & Construction Ltd | Construction | 2019 |
| Matteo DEL Nero Ltd | Information & communication | 2016 |
| Matthew Collings Limited | Information & communication | 2002 |
| Matthew Foods Limited | Manufacturing | 2009 |
| Matthew James Davis Limited | Professional & scientific | 2014 |
| Maven Recruitment Ltd | Professional & scientific | 2019 |
| Mawa Health Ltd | Information & communication | 2025 |
| MAX Papagno Limited | Wholesale & retail | 2026 |
| MBS Property Maintenance Ltd | Transport & logistics | 2003 |
| Mcdonnell Homes Ltd | Construction | 2025 |
| MCM Global Limited | Transport & logistics | 2015 |
| Mcparker & Co Limited | Real estate | 2024 |
| Mcsmith IT Services Limited | Information & communication | 2002 |
| MDL Recycling Ltd | Administrative & support | 2013 |
| Medi Aesthetics Skin Clinic Ltd | Health & social care | 2018 |
| Media for Education Ltd | Professional & scientific | 2023 |
| Medic-Lead Limited | Manufacturing | 2016 |
| Medios IT Skills for Healthcare Professionals Ltd | Information & communication | 2019 |
| Mednus UK Limited | Administrative & support | 2022 |
| Medway Solutions Limited | Real estate | 2018 |
| Memphis Belle Sandwich Shop Limited | Administrative & support | 2011 |
| MEP Bureau Ltd | Professional & scientific | 2014 |
| Mercantile Data Bureau Limited | Administrative & support | 1984 |
| Mercury Project Services Ltd | Manufacturing | 2015 |
| Meridian Property Limited | Real estate | 2018 |
| Meridien Campus Insights Limited | Administrative & support | 2025 |
| Merton Construction Ltd | Construction | 2025 |
| Metadent (UK) Ltd | Health & social care | 2012 |
| Metcalf Wealth Managers Ltd | Other services | 2020 |
| Meteor Creative Ltd | Arts & recreation | 2016 |
| Meyjer Associates Limited | Professional & scientific | 2001 |
| MF Brokers Limited | Financial services | 2007 |
| MFB Limited | Financial services | 2005 |
| Mgwm Consultancy Limited | Information & communication | 2011 |
| Michael Francis Limited | Transport & logistics | 2024 |
| Michael Sebti Design Limited | Administrative & support | 2013 |
| Mico Holding Ltd | Financial services | 2020 |
| Midnight Sun Translations Ltd | Professional & scientific | 2012 |
| Millers Place (Hinckley) Management Company Limited | Households | 2026 |
| Milletts Electrical Ltd | Construction | 2010 |
| Milletts Renewables Ltd | Construction | 2025 |
| Millstone Park Management Company Limited | Households | 2025 |
| Millwright Place, Tovil (Vistry) Management Company Limited | Households | 2026 |
| Milo Technologies Ltd | Information & communication | 2025 |
| Milton Avenue Limited | Real estate | 2025 |
| Mindful Bricks Ltd | Other services | 2025 |
| Mindful Psychotherapy UK Ltd | Health & social care | 2017 |
| Mindsphere Limited | Information & communication | 2022 |
| Mini Drivers Ltd | Arts & recreation | 2018 |
| Miss MPS Ltd | Administrative & support | 2014 |
| Mitek Mezzanine Systems Limited | Construction | 1991 |
| Mivvy Creative Ltd | Administrative & support | 2017 |
| MJ Berry Building Contractors Ltd | Construction | 2014 |
| MJ Harling & Sons Ltd | Real estate | 2023 |
| Mjknowles Limited | Health & social care | 2019 |
| MJM Building & Investigations Limited | Construction | 2024 |
| MJM Groundworks and Building Services Limited | Construction | 2023 |
| MJW Communications Consulting Limited | Administrative & support | 2015 |
| ML Autos and Recovery Ltd | Wholesale & retail | 2022 |
| Mlae Ltd | Financial services | 2022 |
| MLB Cabling Ltd. | Construction | 2023 |
| MMK Holdings Limited | Transport & logistics | 2004 |
| MMK Solutions Limited | Transport & logistics | 2002 |
| Mmouts Ventures Ltd | Professional & scientific | 2023 |
| MOA Horsemanship Ltd | Agriculture & fishing | 2024 |
| Mode Letting (Franchising) Ltd | Real estate | 2024 |
| Mode Letting Limited | Real estate | 2010 |
| Mode Property Management Ltd | Real estate | 2021 |
| Mode Systems Ltd | Information & communication | 2005 |
| Model Matters Limited | Arts & recreation | 2021 |
| MOL Fiber Limited | Wholesale & retail | 2009 |
| Momentum Property Consulting Ltd | Professional & scientific | 2026 |
| Money Tree Investments (London) Limited | Construction | 2015 |
| Montie Associates Limited | Professional & scientific | 2013 |
| Moomba Productions Limited | Arts & recreation | 2016 |
| Moorfoot Limited | Real estate | 1998 |
| More Storage Limited | Manufacturing | 2004 |
| Mortgage Bazaar Limited | Financial services | 2025 |
| Mortgage Finance Brokers Limited | Financial services | 1990 |
| Mortgages for Business Limited | Financial services | 2007 |
| Mortgages for Landlords Ltd | Financial services | 1984 |
| Motioncrews Limited | Information & communication | 2017 |
| Mould Maker Specialist Ltd | Manufacturing | 2025 |
| Mountsorrel JV LLP | | 2017 |
| Movmenta Limited | Information & communication | 2022 |
| Mozambique Quarry Partners LLP | | 2015 |
| Mozinvest LLP | | 2014 |
| MQ Roofing and Building Ltd | Construction | 2026 |
| MSM Financial Consultancy Limited | Financial services | 2003 |
| Msquare Group Ltd | Construction | 2023 |
| MT66 Ventures Ltd | Financial services | 2026 |
| MTB Direct Limited | Wholesale & retail | 2013 |
| MTB Events Limited | Administrative & support | 2019 |
| Mulberry Developments (Maidstone) 2 Ltd | Construction | 2021 |
| Multiplast Leybourne Limited | Manufacturing | 2016 |
| Munhoun Limited | Information & communication | 2026 |
| Murrani&Co Ltd | Information & communication | 2025 |
| Music at Malling Ltd | Arts & recreation | 2012 |