The Tories have pledged to shut down hardcore pornography websites that don't put in place age-restriction controls, despite experts warning this would be hard to enforce.
Culture Secretary Sajid Javid said, if the party remains in power after the general election, it would act to ensure under-18s were locked out of adult content after a recent Childline poll found nearly one in ten 12 -13 year olds are worried they are addicted and 18% have seen shocking or upsetting images.
Under the Tory proposals the system would be overseen by an independent regulator with the power to compel Internet Service Providers (ISPs) to block sites which failed to include effective age verification.
ISPs could be fined if they did not co-operate.
But NSPCC chief Peter Wanless said: "The easy availability to children of online pornography, much of it extreme, violent and profoundly degrading, is of deepening concern.
"It can leave them feeling frightened, confused, depressed or upset. The number of ChildLine counselling sessions regarding porn more than doubled last year to over 1,100 with some young girls revealing they were being pressured to mimic scenes from adult films.
"Any action that makes it more difficult for young people to find this material is to be welcomed. The key will be making any system work effectively as we know foreign outlets are recklessly flooding the market with films that can be viewed by anyone without any age checks in place."
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Javid said: "If you want to buy a hardcore pornography DVD in a store you need to prove your age to the retailers.
"With the shift to online, children can access adult content on websites without restriction, intentionally or otherwise.
"As a father to four young children, I worry, like every other parent, how easy it is for them to view explicit material.
"That is why we need effective controls online that apply to UK and overseas.
"This is about giving children the best start in life; we do not want to prevent adults from accessing legal content but we do want to protect our children from harmful material, so they are free to develop a healthy attitude to sex and relationships."
Javid told BBC Breakfast an effective age control mechanism might be the use of credit cards.
He added that in some countries, such as Finland, there are EIDs - electronic IDs - in place.
"So there are ways there and there might be new ways in the future. The key thing is, it's not for me or politicians to decide what's effective. That will be the job of a regulator, but it is possible," he said.
Labour culture spokesman Chris Bryant responded: "After five years of inaction by the Tories, this proposal is too little too late. Protecting children from inappropriate material both on and offline should be a priority but the Tories have failed to act quickly enough."
Mother's Union chief executive Reg Bailey said it was "a really welcome development".
He said: "A key recommendation of the Letting Children Be Children review ... was to help parents protect children from inappropriate content on the internet especially pornography.
"Although huge progress has been made, this is a real step forward.
"Whilst I do not underestimate the energy that will be needed to implement this effectively, I am greatly encouraged by the Prime Minister's continuing personal commitment to this task."
Sarah Green, acting director of the End Violence Against Women Coalition, said: "We warmly welcome proposals to better regulate access to online pornography by young people.
"Surveys have shown that more than half of young people have seen online pornography by the age of 14, and that many see it without even seeking it out as links are shared on social networks.
"Research has found that young people's exposure to pornography is linked to beliefs that women are sex objects, and to negative and even fearful attitudes towards sex."