Ken is upstaged by Charles

Ken Livingstone made a big show of going to the theatre last night but was upstaged by Prince Charles, celebrating his 53rd birthday in the company of Camilla Parker Bowles.

The prince and his companion made a private visit to the Piccadilly Theatre to watch Jeremy Sam's hugely successful production of Michael Frayn's farce, Noises Off.

Earlier London's Mayor arrived at the performance with 16 of his support staff in an attempt to encourage Londoners to make the most of the capital's troubled theatreland.

The play, which stars Peter Egan, Susie Blake and Isla Blair, recently broke box-office records when it opened on Broadway but last night's star turn was outside the theatre, not on stage. Eight minutes before the curtain was due to go up, the show began. Two sleek cars pulled up opposite the theatre and Charles and Camilla emerged, flanked by a discreet security detail.

Charles, wearing a dark blue suit and a light blue shirt, and Camilla, wearing a black jacket, black dress and a handsome double-string of pearls, were greeted by members of an eight-strong party of companions, believed to include Dame Maggie Smith and Lord Harewood.

They then moved through a crowd of agog sixth-formers and other theatregoers into the auditorium, leaving the the foyer echoing with teenage squeals and cries of: "It's Charles and Camilla. I don't believe it." However Elizabeth Williams, a teacher at Yateley School visiting the play with her pupils, seemed unsurprised: "He must be following us - about six months ago we went on a trip to see Stones In His Pockets and Prince Charles turned up too. It's very strange."

In a move that will perturb suspicious wives across London, the Mayor urged bosses to take their secretaries out after work - to bolster London's economy. "The theatre trade is having a very difficult time since 11 September," said Mr Livingstone.

"If every boss in London would just take their secretary or secretaries out to the theatre that would get us through it - and it's a good way of saying thanks to the people who basically do all our work for us anyhow. I hope bosses will also take their secretaries out for a good pre-Christmas meal so that our restaurants can survive as well."

At the end of last night's performance Mr Livingstone went backstage to greet the cast while the prince and his friends moved on to dinner.

Sonia Friedman, Noises Off 's producer, said: "It is a marvellous accolade for the show that both Prince Charles and the Mayor have chosen to come tonight.

"Ken is here to encourage people to see theatre in what is a very troubling time for the industry and Prince Charles, Camilla and their friends have come privately - they paid for their tickets - simply to enjoy the performance. It is a marvellous coincidence."