Richard Griffiths, Patrick Stewart and Ken Stott may have taken umbrage at disruptive theatregoers, but none appears to have succumbed to a case of stage rage quite as severe as actor Ian Hart, who allegedly lunged at an audience member on Monday night.

According to a witness, Hart, 45, best-known for playing Professor Quirrell in the Harry Potter films, "exploded with anger" during the curtain call of Speaking in Tongues at the Duke of York's theatre in the West End. The focus of his ire was Gerard Earley, a 38-year-old web developer from south London, whom Hart believed had been talking through his performance.

Exactly what happened is difficult to work out. Earley, who went to see the play with his girlfriend and denies disruptive behaviour, told the Daily Mail that "a wild-looking" Hart definitely jumped from the stage – but he wasn't quite sure if he had been physically attacked. "He lost it and lunged forward. I don't think he hit me," Earley said. "One of the members of staff grabbed him and stopped him attacking me."

Earley said that Hart had shouted from the stage shortly after the interval, telling him to "shut up". Assuming it was part of the show, Earley simply smiled. But towards the end of the play, Earley noticed Hart was staring at him, and as he got up to applaud, the actor left the stage and headed for the stalls. Although co-star John Simm tried to placate Hart, pleading "Leave it! Leave it!", Hart unleashed a furious tirade against Earley for "not respect[ing] him and not respect[ing] what he was doing", said Earley.

Speaking in Tongues, a 1996 play by Australian writer Andrew Bovell, debuted in London at Hampstead theatre in 2000 and was later turned into the 2001 film Lantana. "The plot is a theatrical spaghetti junction," according to the Guardian's Michael Billington, in which four actors – Simm, Hart, Kerry Fox and Lucy Cohu – play nine characters whose lives are entwined.

Hart, who has also played Beatle John Lennon twice, refused to comment in detail on the allegations, but told the London Evening Standard that it was "just a lot of silliness". Earlier in the year, he admitted in an interview that his return to theatre was "an economic necessity" and that he didn't relish doing it. "I simply don't enjoy the process; I don't enjoy the relationship between the audience and the actor – or let's just say that my brain isn't wired up in terms of the response an audience gives you. I just think [after a performance], there you go, finished now, so for me it's just arduous. I find it hard work."

According to reports, Earley has not pressed charges for assault, and Hart does not face police action. The show's producers and Hart's agent have refused to comment.