TRIALS of mandatory internet censorship will begin within days despite a secret high-level report to the Federal Government that found the technology does not work, will significantly slow internet speeds and will block access to legitimate sites.

Commissioned by the Howard government and prepared by the Internet Industry Association, the report said schemes for blocking "inappropriate" content such as child pornography were fundamentally flawed.

If the trials are deemed a success, the Government has earmarked $44 million to impose a compulsory "clean feed" on all internet subscribers in Australia by late next year.

But the report 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 raises serious freedom-of-speech questions, such as who will be held accountable for blocked sites and whether the Government will be pressured to expand the blacklist to cover lawful content, including pornography, gambling sites and euthanasia material.