Hell drivers it was...but I think the truck was a dodge 100 series parrot nose..also called the kew..has it was made in kew,London very simular looking..vents give it away at side of bonnet and a badge sitting higher on the front...may be wrong.
Below dodge kew (parrot nose)
And the leyland comet.
And the hawletts truck from the film..think they were called dodge kew.100 series
But john your a genius...the bodies for leyland comet,dodge kew and ford thames et6 were made by the Briggs motor company...seeing has I mentioned it here's the Thames et6.