| Mernustan Limited | Wholesale & retail | 2025 |
| Merobit Ltd | Professional & scientific | 2023 |
| Merrett Housing Limited | Real estate | 2020 |
| Merrill Heights Management Company Limited | Households | 2007 |
| Merrylees Construction Limited | Construction | 2000 |
| Mersaly Ltd | Other services | 2022 |
| Mersey Couriers Ltd | Transport & logistics | 2019 |
| Mersey Engineering Management Ltd | Wholesale & retail | 2018 |
| Mert Design Services Ltd | Professional & scientific | 2020 |
| Merthyr AI Ltd | Information & communication | 2026 |
| Merthyr Spice Ltd | Hospitality | 2023 |
| Merthyr Tydfil Leisure Trust Limited | Arts & recreation | 2014 |
| Merveille Cleaning Ltd | Administrative & support | 2025 |
| Mervyn Mayes Ltd | Wholesale & retail | 2018 |
| Mervyn Watkins Associates Limited | Administrative & support | 2001 |
| Meryl Asset Management PC | | 2016 |
| Merzook Pharma Ltd | Wholesale & retail | 2024 |
| Mesa Consult Ltd | Professional & scientific | 2020 |
| Mesatari Solutions Ltd | Administrative & support | 2020 |
| Mesen Cardiff Ltd | Real estate | 2023 |
| Mesh Enterprises Ltd | Information & communication | 2025 |
| Meshed Learning Ltd | Professional & scientific | 2023 |
| Mesista Services Ltd | Administrative & support | 2021 |
| Meskoz Solutions Ltd | Wholesale & retail | 2021 |
| Mesolab Services Ltd | Wholesale & retail | 2021 |
| Mesopotamia Limited | Wholesale & retail | 2017 |
| Messibat International Limited | Construction | 2019 |
| Messier Property Management Ltd | Real estate | 2024 |
| Messody Holding Ltd | Information & communication | 2025 |
| MET Executive Travel Ltd | Transport & logistics | 2020 |
| MET Surveyors Limited | Professional & scientific | 2025 |
| Meta Future Green Limited | Water & waste | 2024 |
| Meta HR Limited | Administrative & support | 2021 |
| Meta Neurology Ltd | Information & communication | 2025 |
| Meta Property Management Limited | Real estate | 2016 |
| Meta Support Limited | Wholesale & retail | 2026 |
| Meta SVN Ltd | Education | 2024 |
| Meta Trade & Investment Ltd | Agriculture & fishing | 2022 |
| META1ST Limited | Information & communication | 2023 |
| Metaedge (UK) Limited | Wholesale & retail | 2022 |
| Metafrax Chemicals.Jsc Ltd | Manufacturing | 2025 |
| Metagon Cyber Consulting Ltd | Wholesale & retail | 2020 |
| Metall-Fx Ltd | Manufacturing | 2013 |
| Metals Global Trading Limited | Manufacturing | 2021 |
| Metals South West Ltd | Wholesale & retail | 2011 |
| Metaltrade Limited | Professional & scientific | 2002 |
| Metamet Ltd | Information & communication | 2023 |
| Metanew Limited | Mining & quarrying | 2020 |
| Metarise Ltd | Wholesale & retail | 2025 |
| Metarock Ltd | Information & communication | 2021 |
| Metaspark Limited | Information & communication | 2019 |
| Metatron Limited | Information & communication | 2018 |
| Metaverse Education and Training Applications Limited | Professional & scientific | 2022 |
| Metavireon Ltd | Wholesale & retail | 2025 |
| Metaworks Technology Co., Ltd | Information & communication | 2022 |
| Metaxy Services Ltd | Administrative & support | 2020 |
| METEO365 Ltd | Information & communication | 2000 |
| Meteor Sound Ltd | Information & communication | 2020 |
| Metering Limited | Professional & scientific | 2021 |
| Metflex Holdings Ltd | Construction | 2019 |
| Metfusion Ltd | Information & communication | 2019 |
| Metin Arkham Sales Limited | Wholesale & retail | 2025 |
| Metinvest Capital UK Limited | Financial services | 2013 |
| Metinvest Investments Limited | Financial services | 2013 |
| Metis Energy Limited | Professional & scientific | 2023 |
| Metis Services Limited | Financial services | 2019 |
| Metis Technology Limited | Professional & scientific | 2021 |
| Metmin Ltd | Wholesale & retail | 2018 |
| Metonics Limited | Manufacturing | 2025 |
| Metra SPV Ltd | Real estate | 2019 |
| Metra UK Limited | Real estate | 1998 |
| Metrad International (UK) Limited | Wholesale & retail | 2008 |
| Metro Build Services Ltd | Construction | 2026 |
| Metro City Homes Ltd | Real estate | 2025 |
| Metro Construction Limited | Water & waste | 2013 |
| Metro CUT Ltd | Other services | 2026 |
| Metro Films International Ltd | Construction | 2024 |
| Metro Home Furnishing Ltd | Wholesale & retail | 2019 |
| Metro Services & Consulting Limited | Professional & scientific | 2025 |
| Metro Tax Solutions Private Limited | Professional & scientific | 2025 |
| Metrobio Ltd | Professional & scientific | 2010 |
| Metroform L.P. | | 2016 |
| Metroke Limited | Transport & logistics | 2021 |
| Metrology for the Masses Limited | Professional & scientific | 2013 |
| Metron Surveying Services Limited | Professional & scientific | 2020 |
| Metronomic Limited | Information & communication | 2019 |
| Metrotex Limited | Wholesale & retail | 2023 |
| Metroweld Wales Limited | Manufacturing | 1990 |
| Metsmore Group Pty.Ltd. | | 1992 |
| Metsovaara UK Limited | Wholesale & retail | 2019 |
| Mettar Simulations Ltd | Administrative & support | 2017 |
| Mettle International Limited | Administrative & support | 2011 |
| Metzudat David Ltd | Information & communication | 2024 |
| Meuguiafristyles Ltd | Wholesale & retail | 2025 |
| Meva Global Ltd | Wholesale & retail | 2025 |
| Mewslade (Eastern) Limited | Real estate | 1994 |
| Mexborough 81 Limited | Construction | 2025 |
| Mexelio Recruitment Ltd | Public administration | 2020 |
| Mexican Wave Yachting LLP | | 2023 |
| Meximara Holdings Ltd | Financial services | 2020 |