The trial of a teen actor, accused of raping a 14-year-old boy, heard he head-butted his alleged victim before sexually assaulting him.

The 17-year-old actor from south London, who cannot be named for legal reasons, is accused of a string of sexual assaults on the boy in 2010.

During the second day of a trial at Blackfriars Crown Court, the jury heard the actor, then 15, coaxed his alleged victim to stairwell at a stage school in a London theatre in July 2010 before assaulting him.

The alleged victim told the court: "He pulled down my trousers. He started touching me and said he wanted to see. So I pushed him away.

"I think he was touching my bottom.

"He headbutted me. He pushed me against the wall and was holding me against the wall. His forearms were against my chest."

The court heard how the defendant had pulled down the victim's boxers and put his mouth on his penis for a few seconds.

Prosecutor Timothy Forster asked the alleged victim if he wanted the defendant to touch him and the witness replied "no". He also said he could not remember the defendant asking to touch him.

The witness told the court the assault had been interrupted by a teacher asking who was on the stairwell.

He added: "He told me not to say anything and he went up the stairs. He told me to keep quiet or something I'm not too sure. He was whispering."

Asked why he had not told anyone what happened at the time, he replied: "I was shocked I was scared. Everything that had gone on - I wasn't too sure what to think.

"I was upset and I wasn't sure what was going on or anything. I was scared to say what had happened. I was just embarrassed."

On the opening day of the trial, yesterday, the court was told the actor raped the alleged victim to prove he was bisexual to his girlfriend.

The alleged victim began his evidence yesterday but the hearing was halted when he collapsed in the witness box and had to be given medical assistance.

The defendant denies one count of oral rape in July 2010 and three counts of sexual assault between July and September 2010.

The trial continues.