| Meadmanor Limited | Moreton In Marsh | 1999 |
| Meadows Tech Services Limited | Marybank | 2011 |
| Mechem Limited | Hounslow Middlesex | 2020 |
| MED Control UK Ltd | Immingham | 2025 |
| Medco Energi Thailand (E&P) Limited | Henley-On-Thames | 2005 |
| Mediterranean Energy Exports & Services Ltd | London | 2025 |
| Megarme UK Ltd | Renfrew | 2019 |
| Mehco Petroleum Services Limited | Edinburgh, | 2018 |
| Mehdi Consulting Co. Ltd | Warrington | 2019 |
| Meister Group Chemical Co., Limited | Beckenham | 2025 |
| Melcal Marine UK Limited | Aberdeen | 2013 |
| Meldon Aggregates Limited | Leicester | 2024 |
| Meldrum Projects Limited | Aberdeen | 2022 |
| Melleroy Ltd | Banchory | 2018 |
| Mellex Energy Ltd | Glasgow | 2019 |
| Meltore Global Venture Limited | London | 2010 |
| Melville Bay Ltd | Newmarket | 2010 |
| Mem-Teq Ventures Limited | Stokesley | 2001 |
| Mendell Helium PLC | Perth | 2020 |
| Mendip Basalt Co.Limited(The) | Coalville | 1958 |
| Mennes Group International Ltd | London | 2019 |
| Mensaraj Limited | London | 2026 |
| Meols Projects Services Ltd | Swindon | 2011 |
| Meraki Mining Ltd | London | 2018 |
| Mercat Group Ltd | Bourne | 2026 |
| Mercury Oilfield Services Ltd | Carnoustie | 2016 |
| Merediths Site Services Ltd | Bristol | 2019 |
| Meren Services Limited | London | 2019 |
| Meridian Resources Group Co Limited | Bury St. Edmunds | 2023 |
| Merionethshire Granite Ltd | Blaenau Ffestiniog | 2014 |
| Merlin Drilling Consultancy Ltd | Hereford | 2017 |
| Merlin Energy Resources Limited | Ledbury | 1998 |
| Merlin ERD Limited | Perth | 2007 |
| Merry Consult Ltd | Llandeilo | 2014 |
| Mersey Sand Suppliers Limited | Birmingham | 1998 |
| Merseystone Ltd | Liverpool | 2021 |
| Merthyr (Ffos-Y-Fran) Limited | Merthyr Tydfil | 2007 |
| Merthyr Holdings Limited | Merthyr Tydfil | 2007 |
| Merwil Consulting Ltd | Godalming | 2022 |
| Mescell Petroleum Company Ltd | Stafford | 2022 |
| Mesh Global Limited | Weston Super Mare | 2016 |
| MET Trading Limited | Leeds | 2010 |
| Met-Spar UK Limited | Hope Valley | 2012 |
| Metal Capital Limited | London | 2014 |
| Metalcore Industries Ltd. | Faversham | 2016 |
| Metalis Engineering Limited | Bedlington | 2022 |
| Metaloyd London Limited | London | 2021 |
| Metals Exploration PLC | London | 2004 |
| Metalysis Ltd | Rotherham | 2018 |
| Metanew Limited | Cardiff | 2020 |
| Metaurum International Ltd | Birmingham | 2022 |
| Metaverse Digital Ltd | Slough | 2021 |
| Metcalfe Farms Ltd | Leyburn | 2022 |
| Meteor Mining Company Ltd | London | 2020 |
| Meteortania Ltd | London | 2024 |
| Methax UK Limited | Whiteley | 2016 |
| Metigen Limited | Bolton | 2014 |
| Metra Limited | High Peak | 2001 |
| Metsed Energy Limited | London | 2017 |
| Metstream International Limited | London | 2022 |
| MEY Gold Mining and Trading Ltd | London | 2025 |
| MF Inspection Ltd | Glenrothes | 2013 |
| MFE Engineering Ltd | Bristol | 2024 |
| MFG Inverurie (1998) Limited | Aberdeen | 1978 |
| MFW Resources Ltd | London | 2017 |
| MG Stone Limited | London | 2016 |
| MGH Mechanical Services Ltd | Porth | 2025 |
| MGM Global Solutions Ltd | Greenford | 2017 |
| MGM Rigging Ltd | Blackpool | 2017 |
| Mgmcec Ltd | London | 2026 |
| MGN Well Solutions Ltd | Fraserburgh | 2025 |
| MGS Civils Ltd | Omagh | 2022 |
| MGS Wellservices Limited | Banchory | 2011 |
| MI Pathway Ltd | Westhill | 2024 |
| Mi&Corr Limited | Winchester | 2010 |
| Michael Gott Limited | Sidmouth | 2014 |
| Michal Filipiuk Ltd | Aberdeen | 2023 |
| Michelmersh Brick & Tile Company Limited | Haywards Heath | 1997 |
| Michie Project Services Limited | Inverurie | 2015 |
| Mick George Limited | Maidenhead | 1989 |
| Micromine Limited | London | 2002 |
| Microsalt PLC | London | 2016 |
| Midak Engineering Ltd | Lymington | 2018 |
| Middle East and North America Investment Ltd | London | 2025 |
| Middle East Petroleum (UK) Ltd | London | 2014 |
| Middleford Engineering Projects Ltd. | By Stonehaven | 1998 |
| Middleton Aggregates Limited | Alloa | 2025 |
| Middleton Coal Limited | Darlington | 2018 |
| Midexco Limited | Great Yarmouth | 1974 |
| Midis International Ltd | Norwich | 2024 |
| Midland Aggregates Ltd | Bridgnorth | 2015 |
| Midland Excavator Hire Limited | Ashbourne | 1995 |
| Midland Landfill Limited | Warsop | 1993 |
| Midland Quarry Products Limited | Maidenhead | 1996 |
| Migao Mineral Resources Limited | Kington | 2021 |
| Mike Armitage Consulting Ltd | Cardiff | 2021 |
| Mila Resources PLC | London | 2015 |
| Milaha Offshore Services (UK) Limited | Aberdeen | 2019 |
| Mildstonetouch Limited | London | 2019 |
| Miles Offshore Services Limited | Windsor | 2007 |