British Prime Minister David Cameron will on Monday demand Internet search engines take action to block queries about child sex abuse, threatening legislation if they fail to comply.
"There are some searches which are so abhorrent and where they can be no doubt whatsoever about the sick and malevolent intent of the searcher that there should be no search results returned at all," Cameron was due to say in a speech in London.
"So I have a very clear message for Google, Bing, Yahoo and the rest. You have a duty to act on this—and it is a moral duty."
According to extracts issued by his office, Cameron will give the companies until October to comply, saying all the "great brains" who work for them should be able to overcome any technical difficulties.
"I can tell you we are already looking at the legislative options we have to force action," he will say.
Cameron has been pressuring Internet companies to tackle online abuse for several months, after two high-profile trials over child sex murders in which the killers were both found to have searched for child porn online.
"This is quite simply about obliterating this disgusting material from the net—and we will do whatever it takes," he will say.
Companies like Google say they already remove any abusive images of children as soon as they are reported, and the US Internet giant insists it has a "zero tolerance attitude" to such content.
Jim Killock, head of the Open Rights Group which defends Internet freedoms, said he did not believe the prime minister's proposed 'blacklist' of search terms would have any real impact.
Most child abuse images are circulated in private networks or sold by criminal gangs, he said, and noted that if some search terms are banned, people will simply develop new ones.
In a blog posting, he concluded that the proposed policy "is likely to be of highly marginal impact".
Yvette Cooper, a lawmaker who speaks for the opposition Labour party on home affairs, said the government should invest more money in the Child Exploitation and Online Protection Centre (CEOP).
The state-funded body works with police and other child protection agencies and, under Cameron's plans, would draw up the blacklist.
Explore further: British PM urges Google to boost fight against child porn