The production team of the BBC was denied permission to film on the London Underground. Because of that, sets of the tunnels and the stations were built, which turned out so realistic that when the episodes were broadcast, London Transport accused the BBC of surreptitiously sneaking into a real station for the filming. Many of the cast and crew have fondly remembered this and jokingly said the set designer deserved a knighthood for his work.
Until the 10th of October 2013 this episode was believed to be the only surviving part of the Web of Fear. However, the BBC announced that 4 of the missing 5 episodes had been recovered, leaving only part 3 missing.
Deborah Watling had difficulty acting opposite her father Jack Watling, because the sight of him in old age make-up kept making her laugh.
The scenes in Julius Silverstein's museum were originally meant to take place in The Natural History Museum. The producers were denied permission.