BT should face legal action over its trial of Phorm's information-gathering technology, according to a leading IT lecturer.

Phorm collects data on the web habits of internet users and provides related advertising based on this feedback. About 30,000 users were involved in BT's testing of the technology between 2006 and 2007, but none of them were notified.

An internal BT document, revealing details of the scheme, was published on the whistle-blowing site WikiLeaks earlier this week. The company should now face legal action, said Dr Richard Clayton, computer security expert at the University of Cambridge.

"The BT author seems delighted that only 15-20 people noticed this was happening and looks forward to a new system that will be completely invisible," Clayton told the BBC.

"This is not how we expect ISPs to treat their customers' private communications and since, not surprisingly, it is against the law of the land, we must now expect to see a prosecution."

Approximately 7,000 BT users had a cookie file downloaded to their computers without their knowledge, according to the leaked document.

The full report can be read here.