Earlier this year, we reported on the United Kingdom’s plans to regulate online pornography, specifically at the ISP level. At present, the United Kingdom’s top four ISPs (BT, Sky, TalkTalk and Virgin)—who collectively serve 88 percent of British Internet users—impose varying levels of opt-in porn filtering, but only for new customers.

Prime Minister David Cameron says that’s not enough. In a speech on Monday at the National Society for the Prevention of Cruelty to Children, a nonprofit group in London, the UK leader said that he had a “clear message” for Google, Bing, and other major search engines. “You have a duty to act on this—and it is a moral duty,” he said. “I simply don’t accept the argument that some of these companies have used to say that these searches should be allowed because of freedom of speech.”

Cameron wants search engines to impose a blacklist of search terms that Child Exploitation and Online Protection (CEOP), a division of British law enforcement, would provide. The prime minister also demanded an update from these companies by October 2013.

“If in October we don’t like the answer we’re given to this question, if the progress is slow or nonexistent, then I can tell you we are already looking at the legislative options we have to force action,” Cameron said.

“And there’s a further message I have for the search engines. 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 help overcome them. You’re the people who have worked out how to map almost every inch of the earth from space, who have developed 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. You hold hackathons for people to solve impossible Internet conundrums. Well—hold a hackathon for child safety. Set your greatest brains to work on this. You are not separate from our society, you are part of our society, and you must play a responsible role in it.”

Representatives from Google and Microsoft did not immediately respond to our request for comment.

Cameron added that as soon as next month, 90 percent of public, commercial Wi-Fi networks across the UK would also include “family-friendly filters,” a plan that another children’s charity, the Mother’s Union, had previously told Ars that it would like to see put into place.

“And we are keen to introduce a 'Family Friendly Wi-Fi' symbol which retailers, hotels, and transport companies can use to show their customers that their public Wi-Fi is filtered,” Cameron added. “That is how we’re protecting children outside of the home.”

UPDATE 3:03pm CT: A Google spokesperson wrote to Ars with this statement, without addressing Cameron's specific points on the blacklist and the hackathon: “We have a zero tolerance attitude to child sexual abuse imagery. We use our own systems and work with child safety experts to find it, remove and report it. We recently donated $5 million to groups working to combat this problem and are committed to continuing the dialogue with the Government on these issues."