A computer researcher from the University of Cambridge believes BT should face prosecution for "illegally" trialling the controversial Phorm online advertising system.
Dr Richard Clayton told the BBC that the ISP's use of the technology is "against the law of the land".
Phorm identifies which websites users visit and keywords they use, and uses that data to target advertising towards them. A number of privacy activists have spoken out against the scheme, and at least one organisation – the AntiPhorm Group – has produce software designed to cripple the technology.
Virgin Media and Talk Talk have also held discussions with Phorm with regards to using the technology. It's believed that in order to test the system, BT used private data belonging to its customers to customise the ads served.
"This isn't how we expect ISPs to treat their customers' private communications and since, not surprisingly, it's against the law of the land, we must now expect to see a prosecution," Clayton added.
See the BBC report for more.