In a mea culpa published in February, Greenslade explained how his support for the republican cause “and the use of physical force” had followed a journey that began when he fell in love with Noreen McElhone in 1971. 

Noreen, wrote Greenslade, had been “imbued with a republican spirit” and, early on in their relationship, she introduced him to Patrick Doherty, who would go on to become Sinn Fein’s vice president. At the time Greenslade moved in with Noreen McElhone, her daughter Natascha was just two.

Penny Junor, a Royal biographer, said that while McElhone could bear no responsibility for the “sins of her stepfather”, she believed another actress might have been chosen to play a member of a family in such sensitive circumstances.

“I think it shows a lack of respect [by the programme’s makers],” said Ms Junor, “of course, you cannot visit the sins of the father on the daughter but there are lots of actresses out there. It just feels slightly two fingers.”

Ms Junor suggested the new series of The Crown, which premieres in November next year, will “raise eyebrows in so many ways” because the new series covers “recent history” focusing on the early to mid-1990s and the breakup of the marriage of the Prince and Princess of Wales.

The actress has also acknowledged the influence her stepfather once had on her thinking, although she says that “he politicised me only temporarily, much to his chagrin”.

In an interview in 2009, more than a decade before Greenslade admitted his secret IRA support, the actress said: “I am so glad and grateful he [Greenslade] came along. He was a tremendous influence on me. Roy was a great activist.”

Greenslade declined to comment on Sunday. “I have nothing to say, not a single word, to say about a nonsensical story,” he said.

A spokeswoman for The Crown said: “I don’t think we would comment on that story.” McElhone declined to comment.