New rules to be implemented next year will force pornography sites to prove their visitors are over 18 by using age checkers.
The move by Theresa May's government is part of the recently-passed Digital Economy Act, the first sections of which were just laid out before MPs.
Sites which can be accessed in the UK will be required to install age verification systems by April 2018. This may involve sites asking people to enter credit card details, in order to prove they are over 18.
Film ratings board the BBFC is expected to oversee the rules, although a government spokesperson told BBC News that a formal decision will be made in the autumn.
Whoever the regulator is, according to ArsTechnica they will potentially have the power to deal out fines of up to £250,000 to sites caught breaching them – as well as cutting them off from their sources of advertising in the UK, or being blocked outright by ISPs.
The regulator will also be able to decide exactly what kind of system porn sites need to implement – where that's some kind of credit card authentication, or a link via the electoral roll.
"We have taken steps to implement the new age verification requirement for online pornography as part of our continuing work to make the Internet safer," said digital minister Matt Hancock.
"All this means that while we can enjoy the freedom of the web, the UK will have the most robust internet child protection measures of any country in the world."
Of course, determined porn-seekers could still use VPNs or proxys to bypass their service provider, or attempt to bypass the new law by using peer-to-peer file-sharing sites – many of which are blocked by ISPs for the illegal distribution of copyrighted material.
This loophole was highlighted by Dr Victoria Nash, the lead author of a report on safeguarding children from online pornography commissioned by DCMS.
"The idea you can get a regulatory body up and running in that timeframe seems extraordinary to me. And while I don't have a problem with asking these companies to act responsibly, I don't see it as a solution to stopping minors seeing pornography," she told BBC News.
"It may make it harder for children to stumble across pornography, especially in the younger age range, but it will do nothing to stop determined teenagers,"
