| Maltstone Consulting Ltd | Professional & scientific | 2025 |
| Manm Holdings Ltd | Real estate | 2025 |
| Manta Production Services Limited | Other services | 2011 |
| MAP Surveying & Engineering Ltd | Construction | 2019 |
| Marchant Rigging and Construction Services Ltd. | Administrative & support | 2017 |
| Margaret MAY Commercials Ltd | Real estate | 2021 |
| Mark Jarvis Limited | Arts & recreation | 1964 |
| Marlos Epping Ltd | Hospitality | 2025 |
| Marsavvi Ltd | Information & communication | 2021 |
| Master Gadgets Ltd | Manufacturing | 2020 |
| Master Herb Limited | Wholesale & retail | 2023 |
| Masterclass Group Limited | Administrative & support | 2018 |
| Masterful Jack Limited | Professional & scientific | 2016 |
| Masters Academy LLP | | 2014 |
| Masto Ltd | Hospitality | 2004 |
| Matching Ltd | Professional & scientific | 2012 |
| Matmor Ltd | Professional & scientific | 2023 |
| Mattcupco Ltd | Wholesale & retail | 2022 |
| Maverick Services Limited | Transport & logistics | 2015 |
| Maxgain Investments & Real Estate Ltd | Real estate | 2016 |
| Maximilian Bain Hospitality Limited | Hospitality | 2026 |
| Maxine Mawhinney Ltd | Information & communication | 2013 |
| Mayer Restaurant Limited | Hospitality | 2015 |
| MCCONNECT360 Ltd | Construction | 2018 |
| Mclean Eprr Consultancy Ltd | Professional & scientific | 2023 |
| Mcmillans Solicitors Limited | Professional & scientific | 2021 |
| Mcneil Property Ltd | Real estate | 2023 |
| MD Developments Group Ltd | Construction | 2021 |
| MD Investments Group Ltd | Real estate | 2021 |
| MDA Recruitment Ltd | Administrative & support | 2019 |
| MDA Stripouts and Manpower Solutions Ltd | Construction | 2022 |
| Meadow View Residents Association Limited | Households | 2014 |
| Meded Services Ltd | Education | 2024 |
| Medicas Consulens Limited | Health & social care | 2014 |
| Megabet UK Ltd. | Arts & recreation | 1986 |
| Mekend Ltd | Professional & scientific | 2023 |
| Melanie Stephenson Therapeutic Consulting Ltd | Health & social care | 2019 |
| Melo City Breaks Limited | Hospitality | 2024 |
| MEN in Suits Limited | Professional & scientific | 1993 |
| Meris Ltd | Professional & scientific | 2004 |
| MET Sports Limited | Wholesale & retail | 2014 |
| MET Vale Limited | Real estate | 2002 |
| Metafar Ltd | Wholesale & retail | 2019 |
| Meteor Fit Ltd | Wholesale & retail | 2021 |
| Mfsm Logistic Ltd | Transport & logistics | 2023 |
| MGI 3 City Place Limited | Real estate | 2026 |
| MGI Borehamwood Ltd | Real estate | 2026 |
| MGI Bradford Investment Limited | Hospitality | 2026 |
| MGI Chatham Limited | Real estate | 2026 |
| MGI Crawley Limited | Real estate | 2025 |
| MGI Denmark Hill Limited | Real estate | 2025 |
| MGI DP 1 Ltd | Real estate | 2026 |
| MGI DP 2 Ltd | Real estate | 2026 |
| MGI DP 3 Ltd | Real estate | 2026 |
| MGI DP Portfolio Ltd | Real estate | 2026 |
| MGI Dunstable Limited | Real estate | 2026 |
| MGI Fulham Limited | Real estate | 2026 |
| MGI Grants Investments Ltd | Real estate | 2025 |
| MGI Holdings & Investments Limited | Real estate | 2021 |
| MGI Norwood Limited | Real estate | 2025 |
| MGI Norwood One Limited | Real estate | 2025 |
| MGI Rotherham Limited | Real estate | 2026 |
| MGO Consulting Ltd | Professional & scientific | 2021 |
| Mgtow Ltd | Other services | 2018 |
| Miah Trading Limited | Wholesale & retail | 2024 |
| Michael Barnes Media Limited | Professional & scientific | 2025 |
| Midwinter Holdings Ltd | Financial services | 2023 |
| Midwinter Lets Ltd | Real estate | 2023 |
| Mikaco Interiors Ltd | Construction | 2018 |
| Mild Vintage Ltd | Manufacturing | 2025 |
| Milestone Construction & Refurbishments Ltd | Construction | 2022 |
| Military JET Partnership LP | | 2001 |
| Mill Rental Holdings Ltd | Administrative & support | 2023 |
| Millers Estate Agents (1974) Limited | Real estate | 2011 |
| Mind Runner Ltd | Wholesale & retail | 2021 |
| Mindgarden Media Ltd | Arts & recreation | 2015 |
| Minetta Limited | Wholesale & retail | 2015 |
| Mirage Contemporary Construction Limited | Professional & scientific | 2024 |
| Mirrza Autos Ltd | Wholesale & retail | 2024 |
| Misfit Strength and Conditioning Limited | Arts & recreation | 2022 |
| Mitchcap Ltd | Professional & scientific | 2022 |
| Mitchells GAS Services Ltd | Construction | 2016 |
| Mitford Propco Ltd | Administrative & support | 2025 |
| Mitu Logistic Ltd | Transport & logistics | 2018 |
| MJ Sports BET Limited | Arts & recreation | 2021 |
| MMJ Cleaning Limited | Administrative & support | 2013 |
| MMJ Property Solutions Limited | Administrative & support | 2019 |
| Modesign Ltd | Manufacturing | 2020 |
| Modihome Ltd | Construction | 2024 |
| Mojo Property Developments Limited | Construction | 2020 |
| Molly Jane London Limited | Wholesale & retail | 2022 |
| Momentum Capability Solutions Limited | Professional & scientific | 2015 |
| Montebello Limited | Extraterritorial | 2007 |
| Moore Facility Management Ltd | Administrative & support | 2024 |
| Morlux Limited | Construction | 2024 |
| Mornet Global Group UK Limited | Professional & scientific | 2025 |
| Morph Brazilian Jiu-Jitsu Ltd | Wholesale & retail | 2024 |
| Morph Wellness & Fitness Ltd | Health & social care | 2023 |
| Mosaic Consulting Partners Ltd | Professional & scientific | 2014 |
| Mostrim Property Consultancy Limited | Professional & scientific | 2025 |