The poster on the wall of the London Underground advertising a movie called 'Block-Busters' with Sidney Poitier and Rod Steiger is actually a redrawn version of the poster for In the Heat of the Night (1967), which was released the year this story aired. The Earth-bound stories of this era were said to be set a few years into the future, so perhaps the redressed poster is an attempt by the production team to suggest a sequel to that movie.
A copy of this episode was discovered in 2013, restored and released to iTunes late in 2013. A DVD was released in the UK in February 2014.
John Levene's first credited Doctor Who, he previously appeared as an uncredited Cyberman in the film sequences (All scenes set on the moons surface) in Episode 4 of "The Moonbase", The Director Douglas Camefield took the young actor under his wing and gave him the role of the lead yeti which is the yeti with the gun, the prop melted 3 times during film of this episode alone, the following year Camefield cast Levene in the significantly larger role of Corporal Benton in "the Invasion" which was the start of a 7 year regular appearance of the character and with each new Doctor the character of Benton would receive a promotion.
One reason why the poster for In The Heat of the Night is changed to Block Busters is because the BBC is commercial free and can't advertise products. As this appears to be a location shot, that was possibly a real poster and they had to disguise it somehow.
This episode takes place in the London Underground in 1975.