When he was five, Joseph Erber began putting the music he heard in his head on paper.

On Saturday, the 12-year-old composer listened to the London Symphony Orchestra perform his latest work.When the last notes of "Song Without Words" faded away, the audience burst into applause for Britain's newest musical prodigy.

Erber, the youngest composer ever commissioned to write a piece for the orchestra, walked to the stage of London's famed Barbican concert hall in a pink shirt and white tennis shoes.

Smiling but silent, he bowed and shook hands with conductor Richard McNicol and Edward Vanderspar, the orchestra's principal violist who first spotted his talent.

"I didn't believe that this was going to happen," Erber told BBC Radio 4 before the concert.

Saturday's performance was part of a series geared toward young children, and the audience was filled with hundreds of youngsters and their parents.

"I'm really stunned at how young he is," said London resident Stephanie Jacobs, who brought her 11-year-old son. "His piece was really haunting."

Last spring, Vanderspar, whose son went to Erber's school, heard the young composer perform a piano piece he had written for a competition. Erber won, and his school, St. Bartholomew's Primary School in southeast London, received a piano.

Vanderspar was so impressed that he asked Erber to write a piece for the orchestra, giving him $160 and a painting of St. Bartholomew's Church for inspiration.

"I wanted something that was lyrical, and that's exactly what he produced," Vanderspar said after the concert. "I was surprised at how good it was and how well he wrote it for the viola."

Erber wrote "Song Without Words" for viola and piano, and McNicol orchestrated it for strings, trombones and a tuba.

During the concert, which highlighted famous Russian composers, Erber sat in the audience. He tapped his fingers to sections from Sergey Prokofiev's "Romeo and Juliet" and waved his hands, as if conducting, during Tchaikovsky's third symphony.

But after the intermission, the young composer sat still, hands clasped, and listened to his own piece, a lyrical blend of styles and tempos.

"The ideas just come to me," he told The Associated Press before the concert.

Some have compared Erber to Mozart, who also began composing at five, but his mother, Deborah Roberts, a professional singer, is quick to disagree.

"Look what happened to Mozart - pauper's grave at 34," she told the BBC. "That's the biggest danger - that it might be very difficult to get his feet back on the ground next week."

Erber transferred from St. Bartholomew's to Hurstpierpoint College in Sussex last fall to study music.

While his friends listen to pop groups, Erber, who plays piano and violin, takes pointers from classical composers.

"I don't like cheap chart music really," he said. "I like composers like Debussy."

But he won't limit himself just to classical music. With encouragement from his father, composer James Erber, he has completed a jazz piece and plans to pursue a career as a composer.

"I think it's going to be really exciting," he said of the future.