Factual error: The underground station shown is not St. James Park, which would be 1 stop east on the district line. St. James Park has green and yellow tiles on the wall indicating District and Circle lines. The platform in the film has black and brown tiles, indicating Northern and Bakerloo lines.
Factual error: Churchill's ride on the Underground to Westminster (disregarding whether or not it happened) would have been on either the District or Circle line, both of which, being sub-surface lines, use larger rolling stock. The action took place on a much smaller "tube" type train.