As of 2016, which is the longest motorway in the United Kingdom?

The M6 motorway runs from junction 19 of the M1 at the Catthorpe Interchange, near Rugby, Coventry via Birmingham then heads north, passing Stoke-on-Trent, Liverpool, Manchester, Preston, Lancaster, Carlisle and terminating at the Gretna junction (J45). Here, just short of the Scottish border it becomes the A74(M) which continues to Glasgow as the M74. Its busiest sections are J4-10a at Birmingham and J16-19 in Cheshire as this forms the main route from the East/West Midlands and London to Manchester and Liverpool, These sections are now Smart Motorway.

As of 2016, the M6, as well as combining with the length of the A14 from Brampton (Cambridgeshire) from junction with A1(M), the A74(M) and M74 to the junction with the M8 in Glasgow, forms the longest continuous motorway in the United Kingdom and one of the busiest. 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 M6 is 232.2 mi (373.7 km) in length.