Robert Newton and Richard Burton appear together again three years later in "The Desert Rats" only this time Burton has top billing.
Kenneth Griffith and Richard Burton would appear together again over twenty years later in "The Wild Geese."
As a port Liverpool would have had a mix of nationalities and accents. There was a large Irish and Chinese population (one of the largest Chinese communities in Europe). However in this film the dreadful mix of accents does not include an Irish or importantly the very strong regional Liverpool accent. All the actors seem to settle on vaguely 'Northern' accents, even Richard Burton, however his Welsh accent (at this search stage in his career) is still apparent.
This film should have been set in London, there's no reason why it's set in Liverpool with a dozen different accents being used except the native one, which is Scouse.