A FORENSIC scientist has told a rape trial jury at Worcester that DNA found on a shop assistant's trousers could only match one-in-a-billion men.

Valerie Tomlinson testified that 30-year-old Peter Beckford's DNA profile was detected in a semen sample taken from one leg of the garment.

A new technique called SGM Plus identified the DNA after a jury failed to reach a verdict on Beckford in December last year, Worcester Crown Court heard.

The prosecution alleges Beckford raped a young student working alone at a Worcestershire off-licence after robbing her of cigarettes worth more than £900 at knifepoint.

The woman was left locked in a wire cage until customers who heard her cries alerted police.

Beckford, formerly of Grosvenor Road, Aston, Birmingham, admits robbery but denies rape.

Miss Tomlinson gave evidence that only three men in the entire world would have a similar DNA profile to the one submitted for laboratory tests.

Another forensic scientist, Claire Waters, said a colour test on the woman's trousers in early 1999 identifed visible stains as semen.

But she was unable to obtain a DNA sample and it took a year before Miss Tomlinson was able to identify it using the new method.

John Mitting QC suggested to her that Beckford's saliva might have fallen on the trousers and been the source of the DNA. She said it was "highly unlikely".

Earlier, the student gave evidence that Beckford pulled off one trouser leg before the sex attack in a back room of the shop on January 4, 1999.

Martin Hill was waiting outside the off-licence when the defendant emerged and drove off in a Rover car parked outside.

He took the number and then walked down the side of the locked shop to investigate. He heard whimpering from inside and police were called.

PC Gerry Bale described how he found the woman in a hysterical state, screaming.

She was locked in a metal cigarette cage and was crouched on her hands and knees. PC Bale said her first words were: "He's raped me."

Beckford was arrested a week after the robbery and refused to answer all questions put to him by detectives.

The trial continues.