Apparently there's a little heard-of third Dr Who movie following the two 1960s Dalek movies. It had a limited release in 1972 before being lost forever.
The only clue to it ever having existed is this poster.
And the fact that the editor of TV Action comic saw it at a seedy Tunbridge Wells bijou. He recalled the name of the Doctor's home planet from the film the following week, when a reader wrote in to ask the name of the Master's home world.
Thus a legend was born...