I'm sorry, Helen Mirren, but with this latest crowd-pleaser you broke the golden rule of acting

Plus: This rehang will transform the Tate Britain and a chorus of disapproval for these Cambridge folk

This undated image released by Boneau/Bryan-Brown shows Helen Mirren as Queen Elizabeth II in a promotional photo for Peter Morganís play "The Audience." (AP)

What a moment it must have been when Dame Helen Mirren walked into the street in the interval of the West End production of The Audience in which she plays the Queen and reprimanded a bunch of drummers drowning out her words. It's a great story, that the drummers promoting a festival were confronted by a woman the image of Her Majesty. How they must now be wishing they had been promoting a festival in similar, noisy fashion outside the Donmar theatre when Nicole Kidman was famously appearing there naked. That would have been a confrontation beyond your average drummer's dream.

Dame Helen has been roundly applauded for her intervention, which was followed first by a power cut and then by her explaining to the audience in the theatre what she had just done outside, saying: "We seem to be having a bit of a bad night. Did you hear the drums? Well, actually I just went outside dressed as the Queen and told them not too politely to move on."

But I'm afraid I don't applaud her. Hate to criticise a national treasure and all that, but for this theatregoer there is no greater sin than an actor or actress stepping out of character during a performance.

There's been a bit of it about in recent years. The late Richard Griffiths will always be remembered as the actor who used Mirren-esque language to scold an audience member who had his mobile phone on. Most amusing, but I didn't agree with that either.

I'm even slightly uneasy when actors take to Twitter, as they frequently do, to talk about their characters, often in a detached, jokey fashion.

The estimable Dan Stevens did this occasionally about his role as the romantic lead in Downton Abbey. Never overestimate us viewers. We secretly want to believe these characters are real.

Theatre in particular depends on the magic of the moment, the magic of believing that you are watching a character, not an actor pretending to be that character.

Once Helen Mirren had come to the front of the stage during the play to talk to the audience as Helen Mirren, it will have been a little tricky for the people there that night to make an immediate switch to remembering that she was Elizabeth the Second. As for the shenanigans outside, couldn't a stage manager have made the point to the drummers just as forcefully and fruitily as Dame Helen?

The drummers weren't the only unwelcome noise in town that night. Over at Shakespeare's Globe, Roger Allam, playing Prospero in The Tempest, had to cope with planes and low-flying helicopters overhead. In the words of our reviewer, when the helicopters are especially low he, "invents a great ruminative pause, winces for England, and re-charges the poetry with sarcastic splendour". I think I prefer that to Allam tossing Prospero momentarily aside, coming to the front of the stage, and saying "these bloody helicopters, dontcha just hate 'em." He expanded his character, he played with his character, but he didn't leave his character.

So I'm not with Dame Helen on this one. She won a new set of fans I have no doubt, for her indomitable spirit, fruitiness, humour and extravagant action. But, she came out of character on stage, and that's breaking the spell.

This rehang will transform the Tate

I'm always surprised that changes to the permanent collections of our national museums and galleries receive scant attention compared to temporary exhibitions. They can, and often do, transform the visitor experience. One that definitely will is the re-hang of Tate Britain which is officially unveiled next week. I had an early walk round the re-hang with the head of Tate Britain, Penelope Curtis. The new chronological hang of British art over the centuries is clear and thought-provoking, and certainly makes one feel one is visiting the gallery afresh. What particularly struck me was the decision to place sculptures of the relevant eras in the rooms among the paintings. It's an inspired move which gives a more rounded view of art. And, unlike most of those temporary exhibitions, it's free.

A chorus of disapproval for these Cambridge folk

Your emails in support of my long campaign against booking fees show no let-up in your exasperation with these charges. One reader, Clare Burgess, nominates Cambridge Folk Festival for what she terms the "rip-off award." Apparently, the £2.50 booking fee is swiftly followed by a £6 delivery charge to cover "special delivery costs". Those tickets must be mighty heavy to transport. Ms Burgess lists numerous other frustrations. But I note particularly her sign-off line about the festival: "It had better be good!"

There's the rub. What these fees and charges do is make the event-goer jaundiced before the show has even begun.