The Royal Opera House has been beset by problems since its sophisticated redevelopment but last night a fire alert that evacuated the building was traced to a humble potato.

About 2,000 patrons had to leave the theatre in Covent Garden after a ballerina’s microwaved snack overcooked and set off smoke alarms. 

The hungry dancer was a member of the San Francisco Ballet, the oldest professional ballet company from the United States, which is performing in London this week. Fire crews were called to the building and followed the trail of smoke to the backstage area used by the dancers. 

There they discovered charred potato remains still crackling in a microwave used by the artistes. “The microwave seemed fine but there wasn’t much left of the potato,” a spokesman for the London Fire Brigade said. 

Patrons had to miss gin and tonics during the second interval of the evening’s performance when the smoke alarm sounded. A spokesman for the San Francisco Ballet said: “Nobody has owned up to it yet. The audience waited for about 20 minutes outside. They only missed out on their drinks.”  

After the all-clear, patrons returned to their seats for the final dances of the repertoire, which included Mark Morris’s The Garden, Magritomania by Yuri Possokhov and Balanchine’s Symphony in Three Movements set to a Stravinsky score. 

The Royal Opera House reopened in December 1999 after a $300 million renovation that was two months behind schedule. Faults in the computer system meant that sophisticated set-moving equipment and back drops failed to work properly, leading to the cancellation of about 12 performances. Musicians have also complained about poor lighting.