David Cameron has challenged search engine providers to block images of child abuse as part of sweeping Internet safety reforms.
In a speech to the NSPCC due later today he will warn that access to online pornography is "corroding childhood" as he demands tough action by Internet giants to crack down on extreme content.
The Prime Minister said search engines must block results for searches using blacklisted keywords to stop Internet users accessing illegal images and while he will give the providers an October deadline to introduce the measures, he will caution against any claim that it is beyond their technology.
Evidence in two recent high-profile child murders in Britain has shown that the killers accessed online child pornography. Although search companies have pledged to help remove images from the Internet, Cameron says he wants them to go further.
He will say: "I want to talk about the Internet. The impact it is having on the innocence of our children. How online pornography is corroding childhood. And how, in the darkest corners of the Internet, there are things going on that are a direct danger to our children, and that must be stamped out.”
The Internet industry has already agreed to use the database to proactively scan for, block and remove the images wherever they occur, he will add, but he also wants them to block any results from a blacklist of "abhorrent" search terms compiled by the Child Exploitation and Online Protection Centre (Ceop).
Family-friendly filters that block pornography will be automatically selected for all new Internet customers – though people will be able to choose to switch them off – and Internet providers will also contact millions of existing customers and ask them to decide whether to activate filters to stop children accessing unsuitable material.
Cameron will also call for warning pages which pop up if people try to access illegal content to explicitly spell out the consequences of their actions. In an interview with the BBC yesterday he said that the government was ready to introduce new laws if search engine providers did not offer enough cooperation.
A Google spokesman said: "We have a zero tolerance attitude to child sexual abuse imagery. Whenever we discover it, we respond quickly to remove and report it.
"We recently donated $5m (£3.28m) to help combat this problem and are committed to continuing the dialogue with the government on these issues."
Bing, owned by Microsoft, said it would support education and deterrence campaigns and that it was working with the British government to determine the best industry-wide approach to tackle illegal content.
Yahoo was not immediately available for comment.
Enforcement will also be given a boost as experts from Ceop, which is set to become part of the National Crime Agency, will be given enhanced powers to examine secretive file-sharing networks.
Cameron will praise the work Ceop has already done to disrupt the so-called "hidden Internet", where people share illegal files away from mainstream websites.
"Once Ceop becomes a part of the National Crime Agency (NCA), that will further increase their ability to investigate behind pay walls, to shine a light on the hidden Internet and to drive prosecutions of those who are found to use it.
"So let me be clear to any offender who might think otherwise: there is no such thing as a 'safe' place on the Internet to access child abuse material."
He will also set out proposals to link the storage banks of illegal imagery held by police forces across the country to produce a single, secure database enabling officers from different areas to work together to "close the net on paedophiles".
Cameron, who has faced criticism from Labour over cuts to Ceop's funding, will insist that the centre's experts and the police will be given the powers needed to keep pace with technological changes on the Internet.
But former Ceop chairman Jim Gamble, who resigned in protest over the merger with the NCA, sharply criticised the government's approach, warning that it was not doing enough to deter paedophiles who shared abusive images of children online.
"This government has stood still for two years with regard to Ceop," he told the BBC Radio 4's 'Today' programme.
"Ceop's budget has, in real terms, decreased. There are 50,000 predators we are told by Ceop downloading images from peer-to-peer, yet from Ceop intelligence only 192 were arrested last year. That's simply not good enough.
"We have got to get the balance right. The balance is attack the root cause, invest new money into child protection teams, victim support and policing on the ground. Let's create a real deterrent, not a pop-up that paedophiles will laugh at."
David Cameron will also set out plans for new laws so that videos streamed online in the UK are subject to the same restrictions as those sold in shops.
While it has been a crime to publish pornographic portrayals of rape for decades, existing legislation does not cover possession of this material in England and Wales, a situation that will be changed by the closing of the loophole.