Online blocks on child porn have led to a nearly 70 per cent drop in searches for the material

Online blocks on child porn have led to a nearly 70 per cent drop in searches for the material, a study has revealed.

The first research to examine the global impact of blocking child sexual exploitation material (CSEM) found there was a 'precipitous drop' in searches after the measures were put in place.

Google and Bing, Microsoft's search engine, agreed in November 2013 to remove child abuse images from search results and show warnings when certain search terms were used.

David Cameron had called on search providers to stop failing in their 'moral duty' to protect children and announced that households with children would automatically have filters on their internet service that parents would have to 'opt in' to lift – a victory for the Daily Mail's campaign to protect children from online porn.

The US study, published in the journal Child Abuse & Neglect, analysed search traffic levels for keywords commonly used by people searching for CSEM between January 2011 and August last year.

It found searches for such material dropped by 67 per cent in the final year studied – the period following the introduction of the blocks.

Research author Professor Chad Steel, of George Mason University, Virginia, said the results showed 'technical controls aimed at prevention can be effective'. He said: 'The blocking efforts by Microsoft and Google…had a rapid and significant impact on child sexual exploitation material searches. The results show a precipitous drop in such searches.'

But the study found such searches on Russian search engine Yandex – which has no such blocks – had continued at the same rate. Possession of child porn is not illegal in Russia and its distribution and production is only illegal when it relates to children under the age of 14.

The lack of blocks on some international search engines meant it was still possible to find illegal material.

Professor Steel added: 'Searchers from Russia and other locations where child pornography possession is not criminalised have continued to use these services. Additionally, the same lax enforcement environment has allowed searchers from the US to utilise Yandex with little fear of detection or referral to US law enforcement from the Russian authorities.'

Nearly a third of all searches for CSEM came from smartphones or mobile devices such as tablets.

Last week it was revealed that the number of children being counselled through ChildLine about online sexual abuse has more than doubled in a year. The charity said it carried out 2,842 counselling sessions on the issue in 2013-14, a 168 per cent increase on 2012-13. It had also seen an 87 per cent increase in the number of counselling sessions about online bullying.

Last month the country's most senior judge Lord Thomas said the 'peddling of pornography on the internet' was fuelling violent crime.