Prime Minister David Cameron has issued a stark warning to free-to-access porn sites – restrict underage access or face closure.

The government plans to launch a consultation in the autumn that will seek views on how to best implement measures that will restrict under 18’s access to adult websites.

Industry will be given an opportunity to develop proposals through payment providers and other means. A potential regulatory approach may see primary legislation introduced that would make it an offence in the UK to publish adult material online with age verification controls.

Cameron, said: "Our one nation government is working hard to make the internet a safer place for children, the next step in this campaign is to curb access to harmful pornographic content which is currently far too widely available.

"I want to see age restrictions put into place or these websites will face being shut down."

Campaigners have long voiced concern at the ease at which children can access pornographic material on free to view sites.

The lack of effective safeguards means that explicit content is freely available. This freely available content has led to the top 10 adult sites in the UK accounting for 52% of all site views.

Exposure to pornography at a young age can potentially have an harming effect, a poll by Childline found that nearly one in ten 12 to 13 year olds were worried that they were addicted to adult content, with 18% having seen ‘shocking’ images.

This warning could eventually see ISP’s responsible for blocking access to sites that don’t implement age verification.

David Emm, Principal Security Researcher at Kaspersky Lab, said: "Why not get the ISP to implement it also? After all, my ISP already has my bank details, so there’s no increased risk.

"ISPs could offer me, as the customer, the option of a forced sign-in to connect to the Internet, verifying my identity and age and those of anyone else that I, as account holder, have registered; and blocking inappropriate sites accordingly."

Most ISP’s now are able to offer controls to new customers that limit or prevent access to pornography, while many Internet security products also offer this capability.

While there is technology available to the do the safeguarding, Emm says it can’t replace parenting: It’s possible for filters to get it wrong and let through undesirable content unintentionally. "So it’s imperative that we all learn about the dangers of the online world and talk to our children about them.

"This discussion should start as soon as a child picks up a device and continue as they get older and their needs change. Filters alone cannot protect them; education continues to be the most important defence a parent has against online threats."

As the government seeks to crack down underage access to porn, it is also having to battle users in Westminster from accessing porn during their free time.