Consultation on protecting children from internet porn
The government will consult on new measures to protect children from internet pornography.
Under the plans it would be up to customers to opt in to receiving adult content when they sign up for a broadband contract.
Currently most providers offer a range of filters and tools that have to be set up by parents to block pornography.
Campaigners have said it is too easy for children to access explicit adult content on their phones and computers.
Prime Minister David Cameron is due to meet internet service providers (ISPs) to discuss the measures.
In a statement, Mr Cameron said: "I want to fully explore every option that might help make children safer - including whether internet filters should be switched on as the default, so that adult content is blocked unless you decide otherwise."
Conservative backbencher Claire Perry has accused internet companies of being "complicit" in exposing children to pornography and "dragging their feet" on the issue.
Shadow culture secretary Harriet Harman said "keeping children safe online is a real problem and a concern for millions of parents".
She said: "We need to work closely with the industry to develop blocking technology which is easy to use and effective so that parents have the control they need to protect their children."
Nick Pickles, of civil liberties group Big Brother Watch, described the consultation as a "positive step".
But he added that ministers should concentrate on making it easier for parents to take action rather than restricting access to websites.
He said: "Mass blocking of websites was rejected in the US for breaking internet security and in Holland because it doesn't work and drives criminals underground.
"The government should make clear they will not consider a policy that will make it harder to catch child abusers and put consumers at risk when shopping online.
"As recognised by Ofcom, it is trivial to get around an opt-in blocking system so it would be totally wrong for this to be used as an excuse to spy on all our internet activity."
The children's charity NSPCC said it was not in favour of any "halfway house approach" that would risk children "viewing damaging pornography".
NSPCC chief executive Andrew Flanagan said: "An opt-in system will help provide better protection by blocking unwanted material, which is where industry can play a leading role."
But he said no system was foolproof, and underlined the importance of the role parents played in protecting the children from pornography.
Last year four leading web providers - BT, Sky, TalkTalk and Virgin - said they would offer customers the option to block adult content at the point of subscription.