"Already we have a filter on the internet for all parliament house computers. It blocks some political sites, alternative lifestyle sites and other sites that, while not to my personal taste, are hardly grounds for censorship," he wrote. "Imagine if such censorship was extended to every computer in the country through mandatory ISP filtering. Who would be the ultimate arbiter of what is permissible content?"

Bernardi, who tried to censor Gordon Ramsay by calling for a Senate inquiry into swearing on television in March, is known for his conservative views. The pro-life Senator has questioned whether global warming is caused by human activities, has opposed therapeutic cloning of human embryos and protested against proposed laws prescribing equal treatment of same-sex relationships. In his blog post, Bernardi acknowledged that his position on the web censorship issue would "surprise many" and said "a big part of me wants to support it". However, Communications Minister Stephen Conroy's plan was "so devoid of detail" that it was impossible to form a considered opinion.

Senator Conroy has consistently dodged questions in Parliament about the scheme, particularly surrounding the specific types of content that the Government wants to block. The Opposition, Greens and even NSW Young Labor have opposed the scheme, which will make it difficult for the Rudd Government to pass the required legislation.

The individuals who hold the balance of power in the Senate, the independent Nick Xenophon and Family First's Steve Fielding, have said they would want online gambling sites and hardcore pornography blocked by the filters, respectively. "Parental responsibility cannot and should not be abrogated to government - if it is, our society will only become weaker," Senator Bernardi said. "Yes, illegal content should be banned from the web ... but it is wrong to give the government a blank cheque to determine what is appropriate for us to view on the internet."

The deadline has passed for ISPs to sign up to conduct live trials of the internet filtering scheme, some of which are scheduled to begin before Christmas. However, Senator Conroy has refused to release a list of ISPs that applied. Telstra and Internode have both said they will not take part, while iiNet said it will run a trial purely to show the Government the proposed scheme won't work and Optus's trial will be scaled back to encompass filtering only of a set blacklist of 1300 sites.

The Government's policy includes the mandatory censorship of "illegal" content as determined by a blacklist of up to 10,000 sites, which will be held by the Australian Communications and Media Authority (ACMA). The second tier, which will be optional, will seek to block "unwanted" content that is inappropriate for children. No ISP has announced plans to trial the second tier, which is more draconian and technically difficult as it would involve analysing every piece of content handled by the network.

Internet experts say the real-time analysis of content will dramatically slow network speeds, while some child welfare groups have expressed concerns that the internet filters could be easily circumvented, creating a false sense of security. Lab tests released by ACMA in June found available ISP filters frequently let through content that should be blocked, incorrectly blocked harmless content and slowed down network speeds by up to 87 per cent.

Recent tests of software-based internet filters by consumer advocacy group Choice found they were more than capable of blocking offensive material, which raised questions around the need for mandatory ISP-level filters. The previous government provided client-level software filters for free via netalert.gov.au, however, Senator Conroy has said the NetAlert scheme will be shut down by the new year.