| MCM Supply Ltd | Transport & logistics | 2021 |
| MCM Travel & Transport Limited | Other services | 2019 |
| Mcmillan Luxury Estate Limited | Real estate | 2014 |
| Mcmo Motors Ltd | Wholesale & retail | 2026 |
| Mcnicholas Energy and Civil Resourcing Ltd | Construction | 2019 |
| Mcol Ltd | Administrative & support | 2026 |
| MCONN68 Ltd | Transport & logistics | 2026 |
| Mcquade Ltd | Real estate | 2015 |
| Mcqueen Event Limited | Other services | 2022 |
| MCR Residential Property Limited | Real estate | 2025 |
| MCR Trucking UK Ltd | Transport & logistics | 2016 |
| MCR UK Trading Ltd | Wholesale & retail | 2015 |
| Mcritchie Media Ltd | Information & communication | 2010 |
| Mcshane Project and Building Consultancy Limited | Professional & scientific | 2022 |
| Mcsorley Lewis Law Ltd | Professional & scientific | 2012 |
| Mcsp Limited | Real estate | 2010 |
| MCT Training Limited | Administrative & support | 2017 |
| Mctaggart: the Unspoken Truth Media Company Limited | Information & communication | 2025 |
| Mcwe Limited | Wholesale & retail | 2019 |
| MD Beauty Ltd | Other services | 2016 |
| MD Direct Limited | Wholesale & retail | 2019 |
| MD GP Ltd | Construction | 2025 |
| MD Hereford Ltd | Health & social care | 2026 |
| MD Monte Ltd | Information & communication | 2019 |
| MD Online Shopping Ltd | Wholesale & retail | 2025 |
| MD Telecom Communications Ltd | Construction | 2018 |
| MD Trans Europe Limited | Transport & logistics | 2017 |
| MD Works Ltd | Households | 2022 |
| Md.Iku Ltd | Administrative & support | 2016 |
| MDA Consult Ltd | Professional & scientific | 2009 |
| MDA Renewables (Bess) Ltd | Energy | 2026 |
| MDA Renewables (Caers 1) Ltd | Energy | 2013 |
| MDA Renewables (CARDIFF1) Ltd | Energy | 2015 |
| MDA Renewables (Pembs 1) Limited | Energy | 2011 |
| MDA Renewables Limited | Energy | 2011 |
| MDA UK Investments Limited | Financial services | 2011 |
| Mdab Aviation Ltd | Wholesale & retail | 2023 |
| MDB Heating & Repair Limited | Construction | 2019 |
| MDB Heating & SON Limited | Construction | 2021 |
| MDC Freight Limited | Transport & logistics | 2019 |
| MDD Plus Ltd | Transport & logistics | 2019 |
| Mddm Ltd | Transport & logistics | 2018 |
| MDH Stores Ltd | Wholesale & retail | 2023 |
| Mdigital Consultancy Limited | Information & communication | 2017 |
| MDJ Electrical Design Services Limited | Professional & scientific | 2014 |
| MDJ Management Ltd | Administrative & support | 2015 |
| MDK Cardiff Limited | Hospitality | 2025 |
| MDK Outsourcing Ltd | Construction | 2024 |
| MDK Ventures Ltd | Information & communication | 2015 |
| Mdkdeva Food PVT Ltd | Hospitality | 2025 |
| MDM Drywall Ltd | Construction | 2019 |
| MDM Safe Home Limited | Construction | 2020 |
| MDP Mechanical Services Limited | Construction | 2013 |
| MDS United Enterprises Limited | Wholesale & retail | 2024 |
| Mdscomms Ltd | Information & communication | 2018 |
| MDX Services Limited | Construction | 2021 |
| ME, My Skin and I Limited | Wholesale & retail | 2019 |
| ME2YOU Global Limited | Transport & logistics | 2019 |
| MEA Consulting Group Limited | Administrative & support | 2018 |
| Meack Co., Ltd | Professional & scientific | 2026 |
| Meadi Restaurant Limited | Hospitality | 2020 |
| Meadow Consultants Limited | Professional & scientific | 2016 |
| Meadow Developments (WAL) Ltd | Real estate | 2019 |
| Meadow Group (WAL) Ltd | Financial services | 2019 |
| Meadow James 2 Limited | Real estate | 2026 |
| Meadow James Capital Limited | Real estate | 2023 |
| Meadow James Holdings Limited | Real estate | 2025 |
| Meadow James Ltd | Real estate | 2023 |
| Meadow Road Site (UK) Limited | Administrative & support | 2016 |
| Meadowbrook Investments Limited | Professional & scientific | 2004 |
| Meadowcroft Site Services Ltd | Professional & scientific | 2015 |
| Meadowside Apartments Management Company Limited | Households | 2007 |
| Meadride Limited | Information & communication | 2020 |
| Meads Court Management (Chepstow) Limited | Households | 1989 |
| Mears Property Services Ltd | Real estate | 2023 |
| Measure Acp-Uk Ltd | Professional & scientific | 2017 |
| Measureland Limited | Construction | 2023 |
| Measy Ltd | Other services | 2025 |
| Meat Emporium Ltd | Wholesale & retail | 2018 |
| Meat Feast Ltd | Hospitality | 2025 |
| Meat House London Limited | Hospitality | 2015 |
| Meat in Flame Ltd | Wholesale & retail | 2015 |
| Meating Point Cardiff Ltd | Hospitality | 2020 |
| Mebh Ltd | Wholesale & retail | 2022 |
| MEC Coffee Limited | Wholesale & retail | 2019 |
| MEC Consult Ltd | Professional & scientific | 2024 |
| Mecatek Limited | Manufacturing | 2015 |
| Mechamet Limited | Manufacturing | 2018 |
| Mechanical Automated Site Services Ltd | Administrative & support | 2019 |
| Mechanical Management Consultancy Limited | Professional & scientific | 2018 |
| Mechfleet Logistics Limited | Transport & logistics | 2025 |
| Meco Mining Equipment Limited | Manufacturing | 1948 |
| Mecor Ltd | Construction | 2019 |
| MED Blue Tours Ltd | Administrative & support | 2024 |
| MED Concept Ltd | Professional & scientific | 2018 |
| MED Development Ltd | Construction | 2019 |
| MED Valves Co. Ltd | Extraterritorial | 2018 |
| MED94 Ltd | Public administration | 2025 |
| Medaid Services Ltd | Education | 2015 |
| Medass Partners LLP | | 2022 |