British singer Amy Winehouse launched an "unjustifiable" attack on a female fan who politely asked her for a photograph at a charity ball, a court heard on Thursday.

The 25-year-old songstress -- said to be on the road to recovery from her drug addiction -- denies beating Sherene Flash, a dancer, in an incident in Berkeley Square, central London, on September 26.

Wearing a smart grey suit and surrounded by bodyguards, she made no comment as she braved a barrage of cameras before the trial got underway at City of Westminster Magistrates' Court.

Prosecutor Lyall Thompson said the "Back to Black" singer seemed to be under the influence of alcohol or "some other substance" when she struck Flash in a dressing room at the event shortly after midnight.

Flash was taking a photograph of Winehouse when a drunken friend of the dancer, Kieran Connelly, tried to get into the picture. At this point the singer punched Flash to her right eye, Thompson said.

"Miss Winehouse may have felt she had generously agreed to be photographed on her own and not with a drunken stranger," he said.

"This was a deliberate assault by Miss Winehouse. There was nothing accidental about Miss Winehouse's actions," he added, saying the singer used "deliberate and unjustifiable violence."

"She reacted badly to a polite request," he said.

Winehouse won five Grammy awards off the back of her 2006 second album "Back to Black" and the hit single "Rehab", but has since been engaged in a well-documented struggle with drugs.

Her mother Janis said earlier this week that she was feeling better after an eight-month stay in the Caribbean, telling a magazine that the singer "looks better than she has in a long time."

Last week she was granted a "quickie" divorce from her estranged husband Blake Fielder-Civil after two years of marriage, on the grounds of her adultery.