Arrests and convictions for internet child porn offences have quadrupled in the past two years, it has been revealed.

Home Office figures showthat 2,234 people were cautioned or charged with crimes in England and Wales in 2003, compared with 549 in 2001 and 870 in 2002.

Children's charity NCH pointed out that both figures were huge increases on the 35 offences recorded in 1998, when the legal framework for child pornography crimes was established. NCH said the rise underlined the urgent need for a national centre to combat online paedophiles to be set up.

John Carr, the charity's internet safety adviser, said the figures reflected the arrests made during Operation Ore. "But given on-going police activity, the worry is that they represent not a blip but a new 'normality'. Many police admit that they are still only touching the tip of a very ugly iceberg," he said.

Mr Carr said NCH wanted a national police centre established as soon as possible. "There is now widespread agreement about the need for a new, high-powered national centre to tackle internet crimes against children. The only thing there is not yet an agreement about is who should pay for it. We hope ministers can resolve this very soon."

The call was given added weight yesterday following a report by Her Majesty's Inspectorate of Constabulary, which found that child abuse officers in many police forces were spending large amounts of time investigating Internet child porn.

In one force, staff said they were spending about one-third of their time on cyber-crime, even though a large number of the cases "did not involve ongoing child protection concerns". Some said that it was distracting them from investigating child abuse in the real as opposed to the virtual world.

NCH has also called on internet service providers to block access to known child porn websites. The charity will ask Charles Clarke, the Home Secretary, to investigate how many UK-based ISPs in the UK have yet to block access. "Child pornography on the internet is a modern curse and ISPs have a critical part to play in stamping it out," Mr Carr said.

BT and Vodafone have already restricted access to these websites, and he said others had to follow suit or legislation compelling them to do so would have to be introduced.

Operation Ore was launched when American investigators supplied credit card details of 6,500 Britons who entered a US pay-per-view portal to gain access to some 300 websites carrying images of child abuse.

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