(1956, James Stewart, Doris Day)

“Alfred Hitchcock film opens with Stewart, Day and son riding a bus in Morocco. Later on, London Transport double deckers are shown outside Albert Hall and other London locations.” (thanks Bill Vandervoort).
The Moroccan bus is a Floriat C14; other buses seen are a Bedford A tractor and trailer airport bus, a Chausson APH-52, a BEA AEC RF/Park Royal, and two London Transport RT-family buses.
This is a remake of Hitchcock's The Man Who Knew Too Much (1934) .