AN investigation by the police and the prison service was under way last night after a serial sex offender sent his victims lewd letters from prison.

Lawrence Petch sent correspondence, including a birthday card, to more than one girl while serving his sentence at Acklington prison, in Northumberland.

The 54-year-old was jailed for six years at Teesside Crown Court in April last year after pleading guilty to taking indecent photos of a child, sexual activity with a child, making payment for sexual services, and causing a child to engage in sex acts.

The court heard Petch made hundreds of videos of naked teenage girls, showed them porn and made them dance naked for him at his home in Parker Terrace, Ferryhill, County Durham, after plying them with vodka and wine. His victims, who were aged between 12-years-old and 16-years-old, were filmed in a bedroom labelled Sex Club.

A Prison Service spokesman said last night an investigation had been launched into allegations Petch had sent letters to victims, including asking one to pose in her underwear when he is released.

He said: "A full and thorough investigation into these issues is taking place. We are deeply concerned at the issues the case has raised and are very sorry to learn of the distress to the victims and their family members."

He added that the Prison Service did not routinely check prisoners mail and that it was not always possible to prevent inmates contacting members of the public.

Petch has been banned from working with children, put on the sex offenders' register for life and ordered to be on extended licence for seven years when he is released.

In 1993, he was jailed for two and a half years for indecently assaulting a 12-year-old girl and showing porn to teenage girls at his former house in Helmsley Close, Ferryhill. The house was unmasked as a vice den and detectives found blue movies, porn magazines, skimpy clothing and sex aids.

He had previous convictions for indecent assault and showing indecent images to children when he was jailed in May 1993.

Durham Police said last night an investigation into allegations of intimidation was being carried out.