In a victory for the Daily Mail, David Cameron will announce the move today among a series of measures cracking down on against the tide of web sleaze.
The Prime Minister will warn that internet pornography – much of it easily accessible to youngsters – is "corroding childhood".
By the end of next year, all 19million UK homes currently connected to the net will be contacted by service providers and told they must say whether family-friendly filters that block all porn sites should be switched on or off.
From the end of this year, all new customers setting up a broadband account or switching provider will have the filters automatically switched on unless they opt to disable them to allow sites with "adult content".
“The Daily Mail has campaigned hard to make internet search engine filters “default on”. Today they can declare that campaign a success”, Mr Cameron said.
"We are taking action to help clean up the internet and protect a generation of children from often extreme online pornography".
Other measures being announced by Mr Cameron today include adult content filters on all new mobile phones, a bar on accessing adult content through public wi-fi and calling in Ofcom to regulate industry progress. Internet giants such as Google will be told they have a "moral duty" to do more to stop child abuse images being accessed.
There has been growing alarm at evidence that a third of children have accessed online pornography by the time they reach ten. Six in ten parents now say they are worried or very worried about their sons and daughters seeing violent and sexual material on the web.
In his landmark speech at the NSPCC, Mr Cameron will say: "Not long ago, access to the internet was mainly restricted to the PC in the corner of the living room, with a beeping dial-up modem, downstairs in the house where parents could keep an eye on things"
The Prime Minister will add: "I’m not making this speech because I want to moralise or scaremonger, but because I feel profoundly as a politician, and as a father, that the time for action has come. This is, quite simply, about how we protect our children and their innocence".
Mr Cameron will announce that in future deciding about family-friendly filters will be a required part of the set-up process for installing an internet connection.
"By the end of next year, they will have contacted all of their existing customers and presented them with an unavoidable decision about whether or not to install family friendly content filters.
"We are not prescribing how the ISPs should contact their customers – it’s up to them to find their own technological solutions. But however they do it, there will be no escaping this decision".
