Part of the disturbing nature of the drowning scene came from the fact that Tom Baker suffers from aquaphobia and thus was experiencing a real fear of drowning during filming. Baker was reportedly so worried of the cliffhanger scaring children that he visited a random family to watch the episode with them and hear their responses.
The freeze-frame ending to this episode is one of the most controversial scenes in the history of the series. It was the subject of a complaint by Mary Whitehouse following its transmission and she received an apology from the Director-General of the BBC, Charles Curran, who acknowledged that the violence of the scene was too strong. The master tape was edited following her complaint to remove the final seconds. However, the edited footage survives due to a U-matic recording made by BBC Enterprises and a domestic recording made by fan Ian Levine. This footage was used to restore the episode's original ending for the serial's DVD release in 2009.
Director David Maloney admitted on Serial Thrillers (2004) that looking back in retrospect, he had come to accept that the scene at the end of this episode went inadvertently a bit too far.
Graham Williams, who took over from Philip Hinchcliffe as producer, actually agreed with Mary Whitehouse and senior BBC executives that the cliffhanger was too strong. He was quoted: "I thought Philip was wrong to let the drowning sequence in The Deadly Assassin go through, because the violence was too realistic and therefore could be imitated. Even on Z Cars (1962) one did not show a fight using a broken bottle, for precisely that reason."
This episode was watched by 13 million viewers on its original transmission.