A LANDMARK overseas court ruling has raised fresh doubts over a controversial police tactic used in dozens of criminal cases, including in securing the conviction of Daniel Morcombe's killer.

Canada's highest court has ruled that elaborate ''Mr Big'' stings, where suspects are pulled into a fake criminal gang and pressured into confessing, can be abusive and prejudicial, leading to wrongful convictions and serious cases of police misconduct.

But the legal community is divided over how far-reaching the ramifications could be in Australia following the overseas decision.

Brisbane criminal defence lawyer Tim Meehan said the ruling will have a ''massive impact'' because past court judgments on Mr Big stings have relied heavily on Canadian rulings, where the undercover police method was first invented and crafted in the 1990s.

''The fact that the birthplace of this scenario is tearing back significantly on the utility of it, I think that can only have a massive impact on how the Australian courts will look at it,'' he said.

More on this at Brisbanetimes.com.au