The government has dropped a plan to use strict age verification checks to stop under-18s viewing porn online.
It said the policy, which was initially set to launch in April 2018, would "not be commencing" after repeated delays, and fears it would not work.
The so-called porn blocker would have forced commercial porn providers to verify users' ages, or face a UK ban.
Digital Secretary Nicky Morgan said other measures would be deployed to achieve the same objectives.
The government first mooted the idea of a porn blocker in 2015, with the aim of stopping youngsters "stumbling across" inappropriate content.
Pornographic sites which failed to check the age of UK visitors would have faced being blocked by internet service providers.
But critics warned that many under-18s would have found it relatively easy to bypass the restriction using virtual private networks (VPNs), which disguise their location, or could simply turn to porn-hosting platforms not covered by the law, such as Reddit or Twitter.
Likewise, platforms which host pornography on a non-commercial basis - meaning they do not charge a fee or make money from adverts - would not have been affected.
There were also privacy concerns, amid suggestions that websites could ask users to upload scans of their passports or driving licences.
It was a plan, said ministers, to protect children from stumbling across pornography - an objective bound to be hugely popular with parents and anyone concerned about child safety. But throughout its troubled life the porn block has met opposition from across the political spectrum.
The critics said it was an attack on civil liberties, it was the government trying to censor the web, it could endanger privacy and any database of porn users would be a honeypot for scammers. Most of all questions were raised about whether it would work, with pornography shared on social media sites not affected by the ban, and savvy teenagers able to use VPNs to get round it.
Now the fifth culture secretary to be in post since the idea was first mooted has dropped the plan. Nicky Morgan insists its objectives can still be achieved via the new regulator envisaged by the recent Online Harms White Paper.
But expect more wrangling about the precise nature of the "duty of care" the watchdog will impose on the pornography websites and how they will be punished for any failings.
In a written statement issued on Wednesday, Ms Morgan said the government would not be "commencing Part 3 of the Digital Economy Act 2017 concerning age verification for online pornography".
Instead, she said, porn providers would be expected to meet a new "duty of care" to improve online safety. This will be policed by a new online regulator "with strong enforcement powers to deal with non-compliance".
"This course of action will give the regulator discretion on the most effective means for companies to meet their duty of care," she added.
OCL, one of the firms offering age verification tools, was not happy about the decision.
"It is shocking that the government has now done a U-turn and chosen not to implement [this]," said chief executive Serge Acker.
"There is no legitimate reason not to implement legislation which has been on the statue books for two years and was moments away from enactment this summer. [This] would have protected children against seeing pornography on the internet, a move which would undoubtedly have been welcomed by all sensible parents in the UK."
But Jim Killock, executive director of civil liberties organisation Open Rights Group, welcomed the news.
"Age verification for porn as currently legislated would cause huge privacy problems if it went ahead. We are glad the government has stepped back from creating a privacy disaster, that would lead to blackmail scams and individuals being outed for the sexual preferences.
"However it is still unclear what the government does intend to do, so we will remain vigilant to ensure that new proposals are not just as bad, or worse."
In June, the porn blocker was delayed a second time after the government failed to tell European regulators about the plan, leading Labour to describe the policy as an "utter shambles".