(1953, Glenn Ford)

At the height of the movie the train with the bomb on it (drawn by British Rail locomotive number 48600) is shunted into the fictional Felsworth Siding, and the population of Felsworth is evacuated. Four buses are seen: during the evacuation two Leyland Titan TD5/MCCW of Salford Corporation are seen, with a light-coloured Bedford OWB.

There is a brief panning shot along Salford 225 (1940 TD5) in which the Corporation coat of arms is seen, and a glimpse of its registration, BBA550:

When the people are told they can return, the two TD5s are seen again, this time in daylight, and the first of them is clearly seen as Salford 12 (ARJ482, a 1939 TD5):

Leading them is a half cab coach in similar livery to the OB, seen side on. Its fleetname begins with S - that's all you see:

Both Titans had been withdrawn from service with Salford in 1951.
Although the train is ostensibly travelling between the North of England and Portsmouth, Bob Wingrove notes that the buses that were withdrawn by Salford in 1951 were sold to Margo's of Streatham in South London. Possibly Margo's supplied them for filming, and it seems unlikely that they would have travelled far for filming. The ReelStreets website identifies the area evacuated as in Chiswick.