| Mark Bishop Services Ltd | Avoch | 2016 |
| Mark Murray Consultancy Limited | Newtonhill | 2026 |
| Mark Rose Limited | Blackpool | 2017 |
| Markham Geopressure Services Ltd | York | 2018 |
| Markieson Ltd | Aberdeen | 2007 |
| Marlow Well Services Ltd | Arbroath | 2010 |
| Marlow Wellservices Offshore Ltd | Arbroath | 2014 |
| Marlowe Geophysical Limited | Oldham | 2006 |
| Marnhull Stone Limited | Sturminster Newton | 1990 |
| Marque OIL & GAS Limited | London | 2016 |
| Mars Mining Limited | London | 2026 |
| Marshall Biostratigraphic Ltd | Manchester | 2019 |
| Marshall Quarry Products Limited | Bridlington | 1996 |
| Marshall.A Services Limited | North Shields | 2024 |
| Martin Buchan Wellhead Specialist Ltd | Memsie | 2013 |
| Martin Enterprise India -UK Ltd | Stanford-Le-Hope | 2025 |
| Martin Mcleod Design Drafting Limited | Hemel Hempstead | 2007 |
| Martin Thompson Services Limited | Norwich | 2017 |
| Martin's Services Trade & CIE Ltd | London | 2023 |
| Martins Farm Limited | Stansted | 2010 |
| Marubeni Copper Holdings Limited | London | 2016 |
| Marubeni North Sea Limited | London | 2004 |
| Marubeni OIL & GAS (Qatar) Limited | London | 2005 |
| Marula Africa Mining Holdings Ltd | Gerrards Cross | 2025 |
| Marula Global Ltd | Carterton | 2012 |
| Marula Metals Processing Ltd | Gerrards Cross | 2025 |
| Marula Mining PLC | Gerrards Cross | 2001 |
| Masika Communications Limited | Brighton | 2005 |
| Mask Subsea Limited | Inverurie | 2019 |
| Mason Bros Quarry Products Limited | Lampeter Velfrey | 1989 |
| Masss Limited | Stroud | 2015 |
| Material Difference Ltd | London | 2025 |
| Matex Energy Ltd | Slough | 2023 |
| Matriarch Minerals UK Limited | Usk | 2025 |
| Matrix+ Consulting UK Limited | Cranbrook | 2005 |
| Matscott Limited | Glasgow | 1997 |
| Mattalica Solutions Limited | Stockton On Tees | 2013 |
| Mattr UK Holdings Ltd. | London | 1991 |
| Mauritania Goldinvest Ltd | London | 2021 |
| Maverick Crude Ltd | Beckenham | 2026 |
| MAW Offshore Services Ltd | Stonehaven | 2017 |
| MAX Innovate Limited | Coventry | 2010 |
| MAX Lifting Ltd | Hull | 2018 |
| MAX Petroleum PLC | London | 2005 |
| MAX Tech Construction Limited | Shepperton | 2019 |
| MAX01 Ltd | Aberdeen | 2021 |
| Maxify Holdings Ltd | Ilford | 2025 |
| Maximance 2030 Ltd | London | 2021 |
| Maxoil Services Limited | Surrey | 2007 |
| Maxol Limited | Sutton Coldfield | 2018 |
| Maxstim Biochemistry Ltd | Manchester | 2026 |
| Maxwell OIL Tools (North Sea) Limited | Aberdeen | 2014 |
| Mayfair Metals & Commodities Ltd | London | 2024 |
| Mayso Ltd | London | 2008 |
| MB Energy Services Ltd | Selby | 2023 |
| MB Geologist Co Limited | Cheltenham | 2015 |
| MB Geophysical Limited | Bristol | 2017 |
| MB Mining Trading Limited | Tower Hamlet | 2021 |
| MB Stratigraphy Limited | | 2006 |
| MBH Engineering Services Limited | Stockton On Tees, Cleveland | 2024 |
| Mbis International Ltd | London | 2019 |
| MC Daid Bros Ltd | Harrow | 2015 |
| MC Daid Quarries Ltd | Londonderry | 2020 |
| MC Fertiliser Resources UK Ltd | London | 2025 |
| Mcaleer Sand & Gravel Ltd | Dungannon | 2005 |
| Mcallister Renewables Ltd | Stirling | 2018 |
| Mcardle Peat Limited | Armagh | 2002 |
| MCC Petroli Limited | London | 2025 |
| Mccaffrey Aggregates Ltd | Belfast | 2010 |
| Mcconnell Consultancy Services Ltd | Elgin | 2023 |
| Mccourt Mining (UK) Limited | Newcastle Upon Tyne | 2012 |
| Mcdaid Plant & Stone Limited | Derry | 2023 |
| Mcewen Services Ltd | Dalry | 2023 |
| Mcfadyens Contractors (Campbeltown) Limited | Campbeltown | 1976 |
| Mcgeachy Mains Limited | Glasgow | 2026 |
| Mcgillan Jones Associates Ltd | Ballynahinch | 2019 |
| Mcgirr Bros Ltd | Omagh | 2020 |
| Mcgowan Taylor Ltd | Bishopton | 2025 |
| Mcgraths Limestone UK Limited | Motherwell | 2019 |
| Mcguire Offshore Solutions Ltd | Aberdeen | 2025 |
| Mcivor Access & Maintenance Ltd | Inverness | 2022 |
| Mckay Engineering (Montrose) Ltd | Montrose | 2013 |
| Mckay Subsea Services Ltd | Montrose | 2004 |
| Mcknight Inspection Ltd | Stockton-On-Tees | 2024 |
| MCL Solutions Limited | Harrogate | 2011 |
| Mclean Inspection Services (Scotland) Limited | Aberdeen | 2018 |
| Mcleans Electrical Ltd | Dundee | 2018 |
| Mcleod Aggregates Limited | Dereham | 2013 |
| Mcleod Construction Materials Ltd | Durham | 2020 |
| MCQ Copper Ltd. | London | 2011 |
| Mcquillan Quarries Ltd | Lisburn | 2015 |
| Mcroy Drilling Consultancy Ltd | Ponteland | 2019 |
| MCS Subsea Solutions Limited | Aberdeen | 2018 |
| Mcwhinney Offshore Logistics Ltd | Fleetwood | 2014 |
| MCX Dunlin (UK) Limited | London | 2007 |
| MCX Osprey (UK) Limited | London | 2007 |
| MDA Trading Limited | Lewes | 2019 |
| MDK Plant Services Limited | Brora | 2019 |
| MDS Oilfield Consultancy Limited | Aberdeen | 2017 |
| MDT Rigging Services (Scotland) Ltd | Fraserburgh | 2024 |