Actor forced Robert Peston to apologise for language she used on Sunday morning show.

Ofcom is investigating the ITV show Peston On Sunday after the actor Miriam Margolyes swore live on air.

The Harry Potter star, 76, said “fuck” last month while telling an anecdote involving the Hollywood star Warren Beatty.

Ofcom said: “We are investigating whether this programme broke our rules on offensive language before the watershed.”

The show’s presenter, Robert Peston, had acceded to Margolyes’ request to use a “bad word”, which had the studio guests – the Tory MP Sarah Wollaston and Labour peer Lord Adonis – giggling.

Peston apologised, and quipped: “You’ve just got me sacked, which was a public service.”

Margolyes appeared to put her hand over her mouth in surprise following the apology.

Earlier, she described how she agreed with the principles of the #MeToo movement, which is shining a spotlight on sexual abuse, but said it had the potential to lose sight of its aims.

“It can overbalance and become a witch-hunt. I think people talking about hand-on-the-knee 15 years ago is not serious enough,” she said. “Rape and pushing into a woman – it’s obvious what’s assault and what isn’t.”