Curran, who describes himself as “a liberal Democrat”, said he made the film in part because of Donald Trump’s successful presidential campaign.

“I felt disgusted by what was happening on the right and their support for this character running for president,” he said. “But I recognised my own hypocrisy in having a very convenient blind spot to Ted in regard to this story. It’s just empty to keep shouting at the other side and not be prepared to take a hard look at your own candidates.

“This is a story that happened 50 years ago and the fact this is a sacred cow we should not speak about was odd to me, and in itself became a motivating factor. I was angry we weren’t allowed to confront the truth.”

Byron Allen, the film’s executive producer, told Variety magazine “some very powerful people . . . tried to put pressure on me not to release this movie”.