| Mahkah Montessori and Early Years Consultancy & Training Ltd | Wholesale & retail | 2026 |
| Mahks Cares Ltd | Information & communication | 2020 |
| Maids in Essex Ltd | Administrative & support | 2022 |
| Maigmike Consulting Limited | Information & communication | 2013 |
| Main Function Ltd | Information & communication | 2017 |
| Main Street Property Solutions Limited | Administrative & support | 2011 |
| Maintenance Care Consultancy Services Ltd | Professional & scientific | 2024 |
| Mairise Ltd | Professional & scientific | 2018 |
| Maisal Ltd | Health & social care | 2022 |
| Maison Rami Ltd | Hospitality | 2025 |
| Maisonify Holdings Ltd | Real estate | 2025 |
| Majilabs Ltd | Information & communication | 2022 |
| Majitha Trading Ltd | Wholesale & retail | 2025 |
| Majo Services Ltd | Construction | 2023 |
| MAK London Group Ltd | Professional & scientific | 2025 |
| Maka Property Group Ltd | Real estate | 2025 |
| Makaeno Consultancy Limited | Health & social care | 2021 |
| Makeup Box Studio Limited | Other services | 2019 |
| Makeup by LIV Summer Ltd | Other services | 2025 |
| Makewright Ltd | Other services | 2016 |
| Making IT Mindful C.I.C. | Health & social care | 2019 |
| Maktat Limited | Health & social care | 2016 |
| Malabar Automobiles Ltd | Wholesale & retail | 2025 |
| Malden Lodge Residents Association Limited | Households | 1997 |
| Maldon Pizza Company Ltd | Hospitality | 2023 |
| Malee Gulem Limited | Real estate | 2025 |
| Malin Construction Developments Limited | Construction | 2025 |
| Malkim Limited | Other services | 2016 |
| Mall Street Foods Limited | Wholesale & retail | 2020 |
| Mallards Place Management Company Limited | Households | 2020 |
| Maltings Apartments Management Company Limited | Households | 2015 |
| Mama Bola Services Ltd | Construction | 2017 |
| Mamma Soleggia Ltd | Wholesale & retail | 2020 |
| Mammothparking Ltd | Transport & logistics | 2026 |
| Mamre Initiative CIC | Education | 2025 |
| Mana Films Ltd | Information & communication | 2024 |
| Manarex Digital Ltd | Information & communication | 2025 |
| Mandant Limited | Extraterritorial | 2002 |
| Mandant Solutions Limited | Information & communication | 1999 |
| Mandruno Healthcare Ltd | Health & social care | 2022 |
| Mangala Services Limited | Health & social care | 2015 |
| Mannvic Investments Limited | Real estate | 2024 |
| Manor Garage Doors Ltd | Construction | 1999 |
| Manor Hatch Roofing Contractors Limited | Construction | 2026 |
| Manor House Property Management Company Limited | Households | 1988 |
| Manor Lodge Management Company Limited | Households | 2000 |
| Manter Properties Limited | Real estate | 2002 |
| MAP Property Solutions Ltd | Real estate | 2024 |
| Mapfumo Hungwe Ltd | Health & social care | 2014 |
| Maple (185) Limited | Households | 2003 |
| Maple Gate NO.1 Residents Company Limited | Households | 1989 |
| Maple Road Limited | Real estate | 2009 |
| Maple Skyline Ltd | Wholesale & retail | 2018 |
| Marathon Couriers Limited | Transport & logistics | 2018 |
| Marayz Healthcare Limited | Health & social care | 2022 |
| Marbles & Cones Properties Limited | Real estate | 2024 |
| Marc-D Consulting Limited | Professional & scientific | 2022 |
| Marconi 53 Group Ltd | Financial services | 2021 |
| Marcopollo Unique Limited | Construction | 2022 |
| Marg Kofi Limited | Health & social care | 2016 |
| Marg's Beauty Hair Salon Ltd | Other services | 2020 |
| Margtop Limited | Health & social care | 2024 |
| Maria Girboiu Ltd | Health & social care | 2018 |
| Marichi Limited | Wholesale & retail | 2017 |
| Maridan Limited | Health & social care | 2015 |
| Maridass Ltd | Transport & logistics | 2018 |
| Mariili Ltd | Transport & logistics | 2024 |
| Marina Slav Ltd | Construction | 2015 |
| Marine House Cardiff Bay Management Limited | Households | 2019 |
| Marion Pearson Ltd | Real estate | 2026 |
| Mariosa UK Ltd | Health & social care | 2024 |
| Mariteck Medical Limited | Health & social care | 2013 |
| Mariusfconstruction Limited | Construction | 2025 |
| Mark Daniel Electrical Ltd | Construction | 2021 |
| Marker Electrical Ltd | Construction | 2010 |
| Market 4 Harlow Ltd | Wholesale & retail | 2023 |
| Market Force Ltd | Professional & scientific | 2007 |
| Market Square (Harlow) LLP | | 2025 |
| Marketing Mouse Ltd | Professional & scientific | 2021 |
| Marksmann Ltd | Professional & scientific | 2018 |
| Marlborough Court (Green Close) Management Limited | Households | 2015 |
| Marquee the Events Limited | Hospitality | 2020 |
| Marquis (Harlow) Limited | Hospitality | 2023 |
| Marr Construction Ltd | Construction | 2023 |
| Marshall Arts (UK) Ltd | Education | 2014 |
| Marshel Rise Ltd | Real estate | 2021 |
| Marson Holdings Limited | Professional & scientific | 1995 |
| Martin Iliev Ltd | Construction | 2017 |
| Martin Laws Limited | Professional & scientific | 2018 |
| Marx Investments Limited | Real estate | 2019 |
| MAS Consults Ltd | Professional & scientific | 2017 |
| MAS Consults Properties Limited | Real estate | 2019 |
| MAS Mechanical Consulting Ltd | Administrative & support | 2021 |
| MAS Proworks Ltd | Construction | 2026 |
| Mash Empire Limited | Administrative & support | 2023 |
| Mashman Professional Services Ltd | Professional & scientific | 2026 |
| Mashudu Limited | Construction | 2017 |
| Mason Campbell Limited | Professional & scientific | 2009 |
| Mason Oliver Brickwork Ltd | Construction | 2020 |
| Master Stitch Ltd | Manufacturing | 2018 |