| Market Insights Ltd | Professional & scientific | 2019 |
| Market Lane Garage Limited | Transport & logistics | 1978 |
| Marketing Monkeys Limited | Information & communication | 2024 |
| Markway Limited | Administrative & support | 1991 |
| Markwick Moss Ltd | Real estate | 2013 |
| Marlan Consulting Limited | Professional & scientific | 2010 |
| Marlow Motors Ltd | Wholesale & retail | 2014 |
| Marpha Ltd | Professional & scientific | 2013 |
| Mars Innovative Ltd | Information & communication | 2025 |
| Marsdale Plastics Limited | Real estate | 1977 |
| Marsdale Properties Limited | Financial services | 2022 |
| Marstef Ltd | Hospitality | 2019 |
| Martdeck Limited | Wholesale & retail | 1990 |
| Martin Property Services Ltd | Real estate | 2026 |
| Martin's Express Ltd | Transport & logistics | 2020 |
| Martins Rentology Private Limited | Real estate | 2025 |
| Marus Export Limited | Wholesale & retail | 2011 |
| Marvels Global E-Market Ltd | Wholesale & retail | 2025 |
| Marvelss Limited | Wholesale & retail | 2023 |
| Mary Mcginty Limited | Real estate | 1998 |
| Marylebone Flowers Ltd | Wholesale & retail | 2023 |
| Mask Property Group Limited | Real estate | 2022 |
| Mason and Forge Limited | Real estate | 2024 |
| Mason Projects London Limited | Construction | 2016 |
| Mason's Gardens Limited | Administrative & support | 2009 |
| Massage Revive Limited | Other services | 2024 |
| Masterminds United UK Ltd | Information & communication | 2026 |
| Mastic Mums Ltd | Construction | 2025 |
| MAT Drylining Ltd | Construction | 2016 |
| Matador Motion Ltd | Information & communication | 2017 |
| Matawan Limited | Construction | 2007 |
| Materials and Corrosion Protection Limited | Professional & scientific | 2018 |
| Math Labs Research Limited | Professional & scientific | 2019 |
| Mathew Wheeler Editing Ltd | Information & communication | 2025 |
| MATHS2ENGLISH Academy Ltd | Education | 2023 |
| Matrix Accounting Limited | Professional & scientific | 2025 |
| Matrix Associates (UK) Limited | Professional & scientific | 2003 |
| Matt Bridge Accounting Ltd | Professional & scientific | 2024 |
| Matt Cowley Company Ltd | Administrative & support | 2017 |
| Matt's Rugs 'N' Floors Limited | Construction | 2016 |
| Matteo Contractors Ltd | Construction | 2018 |
| Matthew Aish Consulting Limited | Information & communication | 2022 |
| Matthew George Hairdressing Limited | Other services | 2011 |
| Matthews Project Services Limited | Professional & scientific | 2024 |
| Maua Design Studio Ltd | Professional & scientific | 2024 |
| Mawdsley Medical Limited | Other services | 2017 |
| MAX & Sons Ltd | Manufacturing | 2020 |
| MAX Heating & Plumbing Ltd | Construction | 2017 |
| MAX Life UK Limited | Wholesale & retail | 2020 |
| Maxa Distribution UK Limited | Wholesale & retail | 2023 |
| Maxem Construction Limited | Construction | 2022 |
| Maxem Limited | Information & communication | 1998 |
| Maxim Eyes (UK) Limited | Professional & scientific | 2004 |
| Maximore Ltd | Construction | 2016 |
| Maximore Properties Ltd | Real estate | 2024 |
| MAY Park London Ltd | Wholesale & retail | 2018 |
| MAY PUB Company Limited | Hospitality | 2019 |
| Maya Grace Ltd | Health & social care | 2023 |
| Maybern Consultancy Limited | Professional & scientific | 2012 |
| Mayfair Staffing Limited | Administrative & support | 2010 |
| Mayflower Ventures Limited | Professional & scientific | 1988 |
| Mayuri Ltd | Wholesale & retail | 2025 |
| Mazarco Limited | Professional & scientific | 1994 |
| Mbaa Future Ltd | Information & communication | 2021 |
| MC Supplements Ltd | Hospitality | 2025 |
| Mcadam Property & Building Services Ltd | Construction | 2019 |
| Mccolls Financial Services Ltd | Financial services | 2020 |
| Mcdyl Ltd | Construction | 2015 |
| Mcfadden Pilkington & Ward LLP | | 2009 |
| Mckeown Fencing Limited | Other services | 2016 |
| Mclaren Maintenance Ltd | Administrative & support | 2008 |
| Mclelland Consulting Limited | Information & communication | 2014 |
| MCM Capital UK Ltd | Real estate | 2017 |
| Mcmary Domiciliary Care Ltd | Health & social care | 2023 |
| Mcpc Consultancy Limited | Professional & scientific | 2021 |
| MCS Capital Limited | Real estate | 2025 |
| MCS Healthcare Limited | Administrative & support | 2023 |
| MD2GO Ltd | Construction | 2026 |
| Mdenis Associates Limited | Information & communication | 2008 |
| Mdgh Consulting Limited | Information & communication | 2019 |
| MDT Fixing Group Ltd | Construction | 2020 |
| ME First Limited | Other services | 2020 |
| ME Operations Limited | Professional & scientific | 2021 |
| Meadway Consultancy Ltd | Real estate | 2026 |
| Measured Media Ltd | Professional & scientific | 2017 |
| MEB Traders Ltd | Other services | 2021 |
| Mechu Real Estate Ltd | Real estate | 2018 |
| MED Automation Ltd | Information & communication | 2023 |
| Meddpicc Ltd | Financial services | 2021 |
| Medgen Ltd | Administrative & support | 2015 |
| Medgen Nursing Services Limited | Extraterritorial | 2018 |
| Medica Prompta Healthcare Group Limited | Health & social care | 2026 |
| Medical Basics Limited | Health & social care | 2016 |
| Medics Help Limited | Health & social care | 2024 |
| Medictouk Ltd | Professional & scientific | 2020 |
| Mediking Ltd | Education | 2023 |
| Mediterranean Wave Limited | Wholesale & retail | 2023 |
| Mediwise Consulting Ltd | Professional & scientific | 2026 |
| Medleg Doctors Limited | Information & communication | 2015 |
| Megam Solutions Limited | Information & communication | 2020 |