But he has since backtracked, saying the mandatory filters would only block content that has been "refused classification" (RC) - a subset of the ACMA blacklist - amid widespread concerns that ACMA's list contains a slew of R18+ and X18+ sites, such as regular gay and straight pornography and other legal content. "That doesn't meet the election promise as far as we're concerned at all," Wallace said in a phone interview.

"The promise was clearly about providing a safer internet environment for children and to do that you need to mandatorily block in the first instance pornography and R18+, and then provide an opt-in system for those adults who want to access it." The debate around internet filtering is now distinctly polarised, with technical experts and online users' lobby groups arguing that trying to censor the internet on a mandatory basis is authoritarian, hinders free speech and is doomed to fail, and religious conservatives arguing the policy does not go far enough. Although the new Government plan to block just RC content will not prevent adults from surfing for porn, it is still fraught with difficulty as the RC category includes not just child pornography but anti-abortion sites, fetish sites and sites containing pro-euthanasia material such as The Peaceful Pill Handbook by Dr Philip Nitschke.

Sites added to the blacklist in error were also classified as RC, such as one containing PG-rated photographs by Bill Henson. And the websites of several Australian businesses - such as those of a Queensland dentist - were classified RC and blacklisted after they were hacked by, as Conroy described, "the Russian mob".

They were on the blacklist even though they changed hosting providers and cleaned up their sites several years ago. It is a criminal offence to publish the ACMA blacklist. Details about legal material contained on the list and sites that were added to it in error were revealed only after the list was leaked and published on the online whistleblower site Wikileaks. To prevent such errors occurring in future and improve transparency, Conroy told a Senate Estimates hearing yesterday that the Government was considering having the secret blacklist reviewed by a panel of eminent Australians or a parliamentary committee.

"It's clear the Government's confused filtering policy will please nobody," said Colin Jacobs, spokesman for the online users' lobby group Electronic Frontiers Australia. "By overreaching and making policy on the run they now have an expensive plan that ... has alienated internet users, the internet industry and even filtering advocates like the Christian lobby."

Eight small internet service providers and Optus are conducting live trials of internet filters and are expected to release their results in July. Wallace acknowledged that parents were ultimately responsible for protecting their children online but he argued that most parents can't keep up with their kids when it comes to technology, so a mandatory filter was the only solution. "It's not the children of responsible parents only that you're concerned about here, it's the children of parents who are either bewildered by the thing or are not responsible and don't protect their children from this unsolicited pornography," he said.

Asked to respond to Wallace's claims that the Government was breaking its election promise, a spokesman for Conroy said: "The Government understands the position taken by the Australian Christian Lobby and has made it clear that the pilot trial will inform the development of our filtering policy, including the potential for ISPs to offer optional ISP content filtering products to provide families a further level of filtering for content such as X and R rated material."