Saying adults have "neglected our responsibility" to protect children from online predators and sexual images, British Prime Minister David Cameron said pornography will now be automatically blocked from the Internet in most U.K. households unless an adult opts out of the default filter.

In a sweeping speech, Cameron said children currently have unprecedented access to online pornography in their own homes, a reality that is resulting in young people developing "distorted ideas about sex and being pressured in a way we have never seen before."

"Many children are viewing online pornography and other damaging material at a very young age and... the nature of that pornography is so extreme, it is distorting their view of sex and relationships," Cameron said in his speech.

He said children can't go to a movie with explicit sexual content, or purchase pornographic magazines if they are underage, but until now there has been little control over what they watch online -- unless their parents choose to put filters in place to block out adult content. And many simply do not.

Now, the default setting on new Internet connections will be to filter out pornographic content. The adult owner of the connection would have to choose to deactivate the filter if they wanted access to such material.

"In no other market -- and with no other industry -- do we have such an extraordinarily light touch when it comes to protecting our children," Cameron said.

"Children can't go into the shops or the cinema and buy things meant for adults or have adult experiences -- we rightly regulate to protect them. But when it comes to the Internet in the balance between freedom and responsibility, we have neglected our responsibility to our children."

Cameron said over a third of children in the U.K. have received a sexually explicit text or email, and one quarter said they had seen pornography that upset them.

"As a father I am extremely concerned by this," Cameron said.

Under the changes already agreed to by the U.K.'s largest Internet providers:

  • The default filter setting will be 'on' for all new Internet connections;
  • By the end of 2014, all existing customers will have to choose whether to install the family-friendly filter;
  • Only someone 18 or older, who set up the account, can choose to remove the filter;
  • Mobile phones will automatically block adult content;
  • Family-friendly filters will be applied to all public Wi-Fi connections;
  • All devices using a home Wi-Fi connection will also block adult content.

Cameron also outlined new efforts to remove access to child pornography from the Internet and to block access to violent sexual images, saying "the search engines are not doing enough to take responsibility" for providing access to such content.

"We need a situation where you cannot have people searching for child abuse images and being aided in doing so," Cameron said.

Cameron said clear, simple warning pages will be put up on sites where child abuse has been identified and removed. If someone arrives at one of those pages, they will be told immediately that they are trying to visit a site containing illegal images.

And if someone is trying to search terms such as 'child' and 'sex,' they will be given a list of options, such as: 'Do you mean child sex education,' or 'Do you mean child gender?'

"Then there are some searches which are so abhorrent and where there can be no doubt whatsoever about the sick and malevolent intent of the searcher that there should be no search results returned at all," he said, describing it as a "blacklist."

Under the new rules, it will also be illegal to possess online pornography depicting rape.

Cameron said he is first asking the U.K.'s large Internet providers to co-operate with the measures, but said he will introduce legislation forcing them to take part if sufficient progress isn't made by the fall.

"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."

He added: "This is quite simply about obliterating this disgusting material from the net -- and we will do whatever it takes."