"... outside her West End theatre while she was on stage. She poses for the cameras on Monday wearing a T-shirt supporting the drummers – but says she would shout at them again if they played outside the theatre while she was on stage."
Video of the original confrontation — with Mirren in costume as the Queen — here.
In the video at the first link, we see Mirren making nice with the drummers, saying things like: "The irony is I love drumming and I love drummers."
From what I've seen over the years, drummers are the least self-aware of the street performers. They have the worst sense of how good they are, what they are contributing to the social space they occupy, how long and how repetitively one ought to go on, and whether anyone at all appreciates what they are doing.
And I'm not even talking about the drumming that goes on in a political protest, where it expresses anger, facilitates chanting, and is prolonged for the purpose of being annoying.