(2001, Michael Caine, Bob Hoskins, Helen Mirren et al)

“At one point in the film, Helen Mirren boards a red RM to go and visit her daughter in a mental hospital. By the time she arrives at her destination, the bus has miraculously transformed itself into a red MCW Metrobus!!!” noted by Steve Phillips, but a review of the film shows the director intended to show two bus trips.
Firstly Mirren boards RM1280 (280CLT) - when filmed this bus was in preservation:

She's seen sitting aboard the RM, and then another bus:

….which turns out to be MCW Metrobus M176 in London General livery, although it appears to have been sold by London General before filming: