Where you get an idea of how crowded England, and in particular the South East is. The worst parts of the M25 are around Heathrow, the M1 and the Dartford Tunnel, where it really is a car park. It once took me two hours to go ten miles from junction 5 (Sevenoaks) to junction 6 (Godstone...what a joke. Obviously the worst times for traffic are weekday mornings and Friday afternoons. Large chunks of the M25 are only six lanes, making traffic problems worse. Sort it out!
The M25 is one of Europe's busiest motorways, but mismanagement means it usually has only six lanes, when compared to Europe's best roads.