| Motty Ltd | Construction | 2019 |
| Mount Residents Association (South Croydon) Limited | Households | 1974 |
| Mouse to House Furniture Ltd | Transport & logistics | 2005 |
| Movr Solar & Renewable Energy Limited | Construction | 2023 |
| Movtime Limited | Other services | 2012 |
| MOX Auto Trader Ltd | Wholesale & retail | 2019 |
| MP Accountancy Ltd | Professional & scientific | 2021 |
| MPM Design & Build Limited | Construction | 2021 |
| Mpsm Ltd | Other services | 2012 |
| MPT Heating & Plumbing Ltd | Construction | 2022 |
| MQ Modern Living Ltd | Wholesale & retail | 2020 |
| MR & Sons Roofing & Guttering Ltd | Construction | 2024 |
| MR Blade 2021 Ltd | Other services | 2021 |
| MR H2O Ltd | Construction | 2014 |
| MR SO Limited | Hospitality | 2016 |
| MR. K W Ltd | Other services | 2018 |
| Mr.Mindweb Ltd | Education | 2025 |
| Mrcs Limited | Administrative & support | 2002 |
| Mrfiftyseven Ltd | Wholesale & retail | 2026 |
| Mrfst Ltd | Information & communication | 2021 |
| MRS Bucket Theatre Ltd | Administrative & support | 2025 |
| MS Architecture Ltd | Professional & scientific | 2018 |
| MS Build & Construct Ltd. | Construction | 2011 |
| MS Current Solutions Ltd | Construction | 2023 |
| MS Flooring Solutions Limited | Construction | 2013 |
| MS Food Delivery Ltd | Wholesale & retail | 2024 |
| MS Graphic Services Limited | Professional & scientific | 2016 |
| MS Survey Solutions Ltd | Information & communication | 2025 |
| MS Tiling Experts Limited | Construction | 2020 |
| MSA Educational Services Ltd | Education | 2025 |
| MSA INT Group Ltd | Financial services | 2025 |
| MSB Management Ltd | Real estate | 2024 |
| Msbi Limited | Information & communication | 2007 |
| MSG Tech Ltd | Wholesale & retail | 2023 |
| MSJ C&D Ltd | Construction | 2023 |
| MSJ Property Investment Ltd | Real estate | 2017 |
| MSM Designs Ltd | Wholesale & retail | 2025 |
| MSM Financial Limited | Professional & scientific | 2025 |
| MSP Carpentry&Joinery Ltd | Construction | 2016 |
| Mspth Ltd | Construction | 2012 |
| MSW Energy Consulting Limited | Professional & scientific | 2022 |
| Msys Limited | Information & communication | 2007 |
| MT Fibres Ltd | Information & communication | 2020 |
| MTL Logistic and Traders Ltd | Transport & logistics | 2025 |
| MTM E-Commerce Group Limited | Wholesale & retail | 2023 |
| MTN Enterprise Limited | Information & communication | 2012 |
| MTN Limited | Professional & scientific | 2018 |
| Mtsomnitechsols Limited | Professional & scientific | 2023 |
| Mucky Skips Limited | Water & waste | 2015 |
| Muddanna Ltd | Health & social care | 2015 |
| Mughira Naik Ltd | Wholesale & retail | 2025 |
| Muhandes Limited | Education | 2019 |
| Mulberry Mews Developments Ltd | Construction | 2025 |
| Mulgrave Accounting Ltd | Information & communication | 2020 |
| Mulgrave Consulting Limited | Professional & scientific | 2017 |
| Mulgrave Hall Limited | Households | 2001 |
| Multi Hands Services Limited | Construction | 2024 |
| Multi-Storey Property Ltd | Real estate | 2019 |
| Multifayre Ltd | Professional & scientific | 2012 |
| Multiserv Limited | Transport & logistics | 2024 |
| Multiverse Estates Limited | Real estate | 2022 |
| Mumbai Treats Ltd | Hospitality | 2024 |
| Mumma J'S Snax Wagon Limited | Hospitality | 2017 |
| Munch Express Limited | Hospitality | 2022 |
| Muneris Limited | Construction | 2009 |
| Munroe Property Management Services LLP | | 2018 |
| Munroe Property Services Limited | Real estate | 2016 |
| Munzur Fish Bar Limited | Hospitality | 2023 |
| Muqeet Ltd. | Real estate | 2020 |
| Murdoch IT Limited | Information & communication | 2011 |
| Murdoch Plasterwork Ltd | Manufacturing | 2024 |
| Murex Group Limited | Financial services | 2016 |
| Murphy Holdings Stockport Ltd | Extraterritorial | 2025 |
| Musab Trader Ltd | Wholesale & retail | 2020 |
| Musi Building Services Ltd | Construction | 2021 |
| Muskat Care Group Ltd | Administrative & support | 2026 |
| Muss Foods Limited | Hospitality | 2024 |
| Mutualcontrol Property Management Limited | Households | 1994 |
| Mvidler Consultancy Ltd | Information & communication | 2019 |
| MVT Group Ltd | Transport & logistics | 2017 |
| MW Garden and Property Services Limited | Administrative & support | 2021 |
| MWR Motors Limited | Wholesale & retail | 2002 |
| My Car Repair Limited | Wholesale & retail | 2024 |
| My Code Solutions Ltd | Information & communication | 2018 |
| My Glam Squad Ltd | Administrative & support | 2016 |
| My Health Needs Limited | Wholesale & retail | 2024 |
| My House Decorating Ltd | Construction | 2017 |
| My Learned Friend Ltd | Professional & scientific | 2021 |
| My Mortgage Group Ltd | Financial services | 2020 |
| My Tax Helper Ltd | Professional & scientific | 2020 |
| My Wellbeing Business Coaching Ltd | Education | 2022 |
| Myana-K Ltd | Construction | 2017 |
| Myco-Mutiny Ltd | Wholesale & retail | 2023 |
| Mycorp Limited | Manufacturing | 2004 |
| Mycreativeblessings Limited | Education | 2025 |
| Mydaily Essentials Ltd | Wholesale & retail | 2025 |
| MYK Plumbing and Heating Services Ltd | Construction | 2025 |
| Mypilates London Limited | Arts & recreation | 2012 |
| Mypl Ltd | Construction | 2024 |
| Myross Construction Co. Limited | | 1974 |