Internet pornographers have been given a final ultimatum to put in place measures to block under-18s from viewing explicit content or face tough new laws to close their websites down.
David Cameron is determined to ensure that adult sites introduce age verification measures and the Government could pass legislation to compel them to do so if they do not agree voluntarily.
But the move is a softening of the position set out by the Tories during the general election campaign when Mr Cameron's party promised it would legislate to put porn websites behind age controls.
Instead, a consultation later this year will set out a range of options, including both a self-regulatory approach and the prospect of a new law.
The legislative approach would make it an offence to publish pornography online in the UK without a system for verifying a viewer's age. The regime could mean the creation of a new watchdog charged with overseeing and enforcing the controls.
The Prime Minister insisted the Government was "working hard to make the internet a safer place for children" and the next step in the campaign is to "curb access to harmful pornographic content which is currently far too widely available".
Mr Cameron said: “I want to see age restrictions put into place or these websites will face being shut down.”
Minister for Internet Security Baroness Shields said: “Whilst great progress has been made, we remain acutely aware of the risks and dangers that young people face online.
"This is why we are committed to taking action to protect children from harmful content. Companies delivering adult content in the UK must take steps to make sure these sites are behind age verification controls."
The consultation, which will be launched in the autumn, will cover all sites available in the UK, including those based overseas, although it was unclear how legislation could be extended to foreign pornographers.
The industry will be given an opportunity to develop proposals to block content through payment providers and other means. The consultation will consider the best form of legislation should voluntary agreements not work.