The M6 motorway is the longest motorway in the United Kingdom. It is located entirely within England, running for just over 230 miles (370 km) from the Midlands to the border with Scotland. It begins at Junction 19 of the M1 and the western end of the A14 at the Catthorpe Interchange, near Rugby before heading north-west. It passes Coventry, Birmingham, Wolverhampton, Stoke-on-Trent, Preston, Lancaster and Carlisle before terminating at Junction 45 near Gretna. Here, just short of the Scottish border it becomes the A74(M) which continues to Glasgow as the M74. Its busiest sections are between junctions 4 and 10a in the West Midlands, and junctions 16 to 19 in Cheshire; these sections have now been converted to smart motorways.

The A74(M) and M74 form a major motorway in Scotland, connecting it to England. The routes connect the M8 motorway in central Glasgow to the Scottish-English border at Gretna. In conjunction with their southward continuation, the M6 motorway, they form one of the three major cross-border routes between Scotland and England. They are part of the unsigned international E-road network E05. Although the entire route is colloquially referred to as the M74, for more than half its length, south of Abington, the road is officially the A74(M); see naming confusion below.