A man has been charged with assault and detained for psychiatric assessment after an attack on British singer Leona Lewis in a London bookshop, police said on Thursday.

Lewis, who won the British television talent show The X Factor and has topped charts around the world, was signing copies of her autobiography at a store in Piccadilly Circus on Wednesday when she was punched in the head.

Police said they had charged Peter Kopwalczyk, 29, of south London with assault. They said he was detained under the 1983 Mental Health Act.

Under the act, people who may have a psychiatric disorder can be held against their will and given treatment.

He will appear at City of Westminster Magistrates' Court on October 26.

My brother saw the whole incident, one fan at the book store told the BBC after the assault. He (the attacker) walked up there with the book, she signed it and, as she looked up, he just punched her.

Lewis, whose debut album entered the U.S. charts at number one in 2008 -- the first British woman to achieve the feat -- was badly shaken but did not need hospital treatment.