"I can't for a moment speculate what's going on but it certainly doesn't seem to be running as a project on time and they're certainly not communicating with the people that they need to - that is, the ISPs that have offered to test this thing," said White. Senator Conroy - despite his promises before Labor was elected that people would be able to opt out of any internet filters - has said the first tier of the Government's censorship policy will be compulsory for all. This would block all "illegal" and "inappropriate" material, as determined in part by a secret blacklist administered by the Australian Communications and Media Authority.

A second tier would filter out content deemed harmful for children, such as pornography, but this would be optional for internet users. Australia's largest ISP, Telstra, and Internode have said they will not take part in the trials. The second-largest ISP, Optus, will run a scaled-back trial of just the first tier, while iiNet, the third-biggest provider, has also said it will only trial the first tier, simply to show the Government that its scheme will not work. The Government said this week it had received 16 applications from ISPs looking to take part in the trials and more details would be available within days but the lack of participation from the major ISPs indicates that the trial participants will be small players with few users.

This may mean the trials will not provide much useful data as to the effects of internet filtering in the real-world. Cooperation from the large ISPs has been so poor that makers of internet filtering hardware - mindful of the revenue they could generate if the internet censorship plan goes ahead - are petitioning small ISPs, offering to provide them with all the equipment they need to take part in the trials.

"I know that some vendors have been approaching ISPs and saying we're happy to support your participation in the trial and then on that basis they put in an application," said Peter Coroneos, CEO of the Internet Industry Association. Greens Senator Scott Ludlam, who has long campaigned against the censorship plan, said the delays in starting the trials indicated the Government may have hit the wall of technical impossibility that the industry had been warning it about for 12 months. "Considering the intention was to launch a live trial before Christmas, we've got a six week delay and no commitment to testing on actual people," he said.

"This isn't a great advertisement for the workability of any large scale scheme. The proposal has always been unpopular, now perhaps the Government is starting to come to grips with what the industry has been saying all along: if your policy objective is to protect children online, this is not the way to go about it." Ludlam posed a series of questions to the Government about the web censorship scheme late last year and responses were received this month.

Asked to provide evidence to support the claimed public demand for filtered internet connections, the Government said the plan was an election commitment. "I don't think it's good enough to refer back to an election promise that no one even knew existed ... they certainly didn't campaign on it," Senator Ludlam said. "You get a sense of the degree of public demand by the fact that the voluntary opt-in [NetAlert] scheme [that was started by the Howard government and provided free software filters] was so barely subscribed that they closed it down."

The Government also admitted that any internet filters it would introduce could be bypassed using easily available technological tools. And despite Senator Conroy claiming that most of the content on the ACMA blacklist was child pornography, the Government revealed that only 674 sites out of the 1370 sites currently listed related to depictions of a child under 18.

506 sites would be classified R18+ and X18+, which is legal to view in Australia but would be blocked for everyone under Labor's mandatory censorship scheme. The policy has attracted opposition from online consumers, lobby groups, ISPs, network administrators, some children's welfare groups, the Opposition, the Greens, NSW Young Labor and even the conservative Liberal senator Cory Bernardi, who famously tried to censor the chef Gordon Ramsay's swearing on television. A recent survey by Netspace of 10,000 of the ISP's customers found 61 per cent strongly opposed mandatory internet filtering with only 6.3 per cent strongly agreeing with the policy.

An expert report, handed to the Government last February but kept secret until December after it was uncovered by the Herald, concluded the proposed scheme was fundamentally flawed. It says the filters would slow the internet - as much as 87 per cent by some measures - be easily bypassed and would not come close to capturing all of the nasty content available online.

They would also struggle to distinguish between wanted and unwanted content, leading to legitimate sites being blocked. Entire user-generated content sites, such as YouTube and Wikipedia, could be censored over a single suspect posting. "It's definitely not going to be workable to get a very significant reduction in access to this [unwanted] content that is available out there - it's fundamentally just not viable," said one of the report's authors, University of Sydney associate professor Bjorn Landfeldt.