Episode: Summer Holiday
AEC Routemaster RM1536 (536CLT) drives through a billboard and over a cliff, then explodes in the final episode. (thanks CCR)
"It was sold to 9-9 Cars, Elstree in January 1984. It's then listed as being scrapped in Kent the same month." (thanks Steven Oliver) This scene was also shown in the Perpetual Motion documentary, from which these screen captures come.
Episode: Demolition
Features a bus, but lots more information needed!