London:
Internet service providers in Britain will be asked to automatically block access to pornography sites unless customers opt in, Prime Minister David Cameron announced on Monday.
Cameron announced the move as part of measures to stop extreme sexual images he said were "corroding childhood."
In a speech to a children's charity, Cameron said that "family-friendly" filters would become the default setting for new customers by the end of the year, and only account-holders would be able to change them.
He also announced a proposal to make it a crime to possess violent pornography containing simulated rape scenes, and said Google and other search engines would be asked to block searches based on certain phrases.
Anti-pornography activists welcomed the announcement, but critics said the measures would be hard to implement.
Cameron, however, said service providers should be able to come up with solutions.
"If there are technical obstacles to acting on this, don't just stand by and say nothing can be done; use your great brains to overcome them," he said.
"You're the people who have worked out how to map almost every inch of the earth from space, who have algorithms that make sense of vast quantities of information. You're the people who take pride in doing what they say can't be done."
But Padraig Reidy of free-speech group Index on Censorship said the proposals amounted to "a kind of default censorship."
"If a filter is set up as a default then it can really restrict what people can see legitimately," he told BBC radio. "Sites about sexual health, about sexuality and so on, will get caught up in the same filters as pornography. It will really restrict people's experience on the web, including children's."