Arriving at London’s Gielgud Theatre wearing a T-shirt supporting the group, she admitted using “a few thespian words” and said the group were “very sweet and stopped the minute they knew I wasn’t just a batty old woman haranguing them on the streets of Soho”.
The 67-year-old said: “In another situation I would have been out here just enjoying it with all the punters.
“Unfortunately, I was having to do a play at the same time.”
The troupe of dancing drummers from As One in the Park, who were promoting their festival for gay and transgender people, were stunned when Dame Helen told them in colourful language to be quiet.
She went outside the theatre in the interval, where she is starring as the Queen in The Audience, for which she has won an Olivier Award, to confront the group.
“I’m afraid there were a few ‘thespian’ words used,” Dame Helen said. “They got a very stern royal ticking off but I have to say they were very sweet and they stopped immediately.
“I felt rotten, but on the other hand they were destroying our performance so something had to be done.”
But the group’s conductor, Liam Emerson, said there were no hard feelings.
“We’ve had lots of members of the public swear at us, but we’ve not necessarily had Dame Helen Mirren dressed as the Queen swear at us before, so it’s quite unique,” he said.
In The Audience, written by Peter Morgan, Dame Helen returns to her Oscar-winning performance as the Queen.
It depicts the Queen in conversation with the many prime ministers who have served during her reign.
Chris Dangerfield, a comedian, was filming the drummers from his nearby balcony when Dame Helen burst through the stage door, gesticulating wildly.
Dangerfield said he could not hear what Dame Helen was saying over the drumming, but “I could tell it was hostile”.
Rufus Wright, who plays Prime Minister David Cameron in the production, also told the musicians to be quiet. On Twitter he wrote: “Just fulfilled a lifelong ambition by bellowing at 25 drummers to shut the f*** up.”
He added: “You should have seen Helen. She came out in full Queen costume and shouted at the drummers too. Honestly. It was breathtaking”