A US military detective would have to question witnesses with a British police officer present not on his own.
A US serviceman in Britain in 1956 would not be permitted to carry a gun let alone fire it at will in the street as the Capatin does in the film.
The emergency vehicles have American-style sirens instead of the more familiar ringing bells.
(Cigarette?) smoke appears for no apparent reason at 55:12 and 55:44.