The torture inflicted by five Wandsworth men on Mary Ann Leneghan and her friend has never been seen before in this country, according to an expert.

Alex Sklan, director of clinical services at the Medical Foundation for the Care of Victims of Torture, said the atrocities would not have been out of place in Sierra Leone.

The news comes after it emerged that four of the six convicted defendants were on probation when they killed the Reading teenager.

Mr Sklan said the sadistic abuse, which included rape, having cigarettes stubbed out on them, being made to strip, having hair cut off, being flicked with boiling water and repeatedly told they would be dead by the end of it all, was about power and control.

He said: "These kind of attacks wouldn't be out of place in somewhere like Sierra Leone.

"People there are aware of this going on and there is some sort of preparation and some sort of fear, but the added factor here is these girls felt perfectly safe.

"This is absolutely the highest level of psychological harm you could impose on somebody.

"The girl who witnessed this, one would expect her to be highly shocked and, I don't know what she's made of, also depressed and having post traumatic stress disorder."

Mary Ann was stabbed to death and her friend, who cannot be identified, was shot in the forehead.

The pair were left in Prospect Park but Mary Ann's friend survived the ordeal and went on to become a crucial witness in the trial.

Drug user Adrian Thomas, 20, of Queenstown Road, Battersea, and fellow gang members Michael Johnson, 19, of Keevil Drive, Southfields, Jamaile Morally, 22, of Brook Close, Balham, and 18-year-old Indrit Krasniqi, of Oxford Road North, Chiswick, were all under supervision by the probation service when the 16-year-old was stabbed to death and her friend shot and left for dead in Prospect Park last May.

The shocking news was revealed after the jury concluded on Monday that Krasniqi was guilty of murder and attempted murder.

Thomas, Morally, Morally's brother Joshua, 23, of Brook Close, Balham, and their friend Llewellyn Adams, 24, of Old Hospital Close, Balham, were all found guilty of the killing at Reading Crown Court on Friday afternoon, while Johnson confessed during the eight-week trial.

Krasniqi was convicted of kidnap and assault on Friday, but found not guilty of two counts of rape.