Following a battle between the Daleks and the Mechonoids today in 1965, school teachers Ian and Barbara finally managed to get back to London, albeit 2 years late. These were the events of The Planet of Decision, the sixth instalment of The Chase. The episode also introduced new male companion Steven Taylor, played by Peter Purves, and it was the final episode to be directed by Richard Martin.
The still images of Ian and Barbara running around London, and the film of them on a bus, were the work of director Douglas Camfield, and were part of the production of The Time Meddler.
In 2010 Steven Moffat demonstrated that he had a problem with two-part stories. After the superb The Pandorica Opens, The Big Bang was more of a damp squib. Too much gimmicky timey-wimey nonsense, and a plot that didn't stand up to close examination.