Gretna, Scotland in the context of Annan, Dumfries and Galloway

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 and runs between Manchester and Liverpool 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.

It incorporated the Preston By-pass, the first length of motorway opened in the UK and forms part of a motorway "Backbone of Britain", running north–south between London and Glasgow via the industrial North of England. It is also part of the east–west route between the Midlands and the east-coast ports. The section from the M1 to the M6 Toll split near Birmingham forms part of the unsigned E-road E 24 and the section from the M6 Toll and the M42 forms part of E 05.

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. 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.