The new ''more likely than not'' test would mean there would have to be a ''greater than 50 per cent chance'' of a person suffering significant harm for them not to be returned, he said.

The change, covering those seeking protection under international treaties against torture and on civil and political rights, was one of many to toughen the process for seeking asylum. It does not apply to those seeking protection under the refugee convention.

While Mr Morrison insists the new law is in line with the approach of Canada, Switzerland and the US, Mr Manne said it was contrary to accepted practice and could carry grave consequences and ''ultimately risk the lives of many''.

''What this does is propose a fundamental deviation from the well-established threshold for assessing someone's risk of facing life-threatening harm,'' he said.

Mr Manne said no case had been made for this and other changes that would ''downgrade due process and impose restrictions on fundamental rights''.