Web is blamed for 20 per cent leap in sex attacks by children

Experts said the behaviour of youngsters was being changed by ready access to sexual imagery.

The number of cases in which children received court orders or warnings for sex offences has jumped by 20 per cent from 1,664 in 2002/03 to 1,988 last year.

A shocking 143 cases involved 12-year-olds. There were 41 in which the accused was 11 and 21 where they were just ten.

Tink Palmer, of the Internet Watch Foundation, warned that the real amount of offending could be far higher because as much as 90 per cent of sexual abuse goes unreported.

She said she had seen cases where children had become addicted to Internet pornography or had been groomed in chatrooms to access it.

The potential exposure to adult pornography was huge compared with in the past, she added.

The NSPCC said its own research has suggested up to a third of all alleged sexual abuse involves young perpetrators.

Kevin Gibbs, co-chairman of the charity's sexually harmful behaviour group, said the Internet had let everybody access pornography more easily, including children from all backgrounds.

He added: "Five or ten years ago it would have been time-consuming and involved a lot of money. But these days it's easy to access pornography online and it's also often free. A child can get at these images within five minutes."

Mr Gibbs said the NHS offers some support through Child and Adolescent Mental Health Services for children displaying worrying sexual behaviour. But waiting lists were long and provision "patchy".

He added: "Early intervention is crucial with these young people. The challenge is that they fall between two Government departments - the Department of Health and the Home Office. We are getting better co-ordination at a local level but we need a lot more services available across the UK."

Pam Hibbert, principal policy officer at Barnardo's, said the charity ran nine dedicated services for children with harmful sexual behaviour.

But child and adolescent mental health services were "hugely oversubscribed", with lengthy waiting lists, and more needed to be done.

Last month, a U.S. study found children are routinely being exposed to Internet pornography, despite filtering systems supposed to protect them.

Access to the Internet via 3G mobile phones had also put pornography into the hands of youngsters.