A former adviser has fiercely condemned the Abbott government for claiming he backs its plan to strip citizenship from foreign fighters at the discretion of the immigration minister without a criminal trial, when he bitterly opposes the idea.



The prime minister, Tony Abbott, told parliament the plan to allow ministers to strip citizenship from terrorists who are dual nationals at the discretion of the immigration minister was “precisely what was recommended by the former independent national security monitor Bret Walker”.



After reading from Walker’s March 2014 report, Abbott said: “That’s exactly what we are doing. We are acting upon the recommendation of Bret Walker SC … because we will never rest until we are confident that the Australian people are as safe as we can make them.”

But Walker has already said publicly his recommendation was for a minister to have the discretion to strip citizenship after a charge had been proven in a court and it had “never occurred” to him that any government would think he had been advising that a minister should have that discretion without any conviction – something the high court would almost certainly find to be unconstitutional.

On Tuesday Walker told Guardian Australia the government should immediately stop misquoting his report to defend the laws it says will be unveiled within a fortnight.

“I am impatient with and I condemn those who persist in reading pages of my report as if they say the government can exercise ministerial discretion after dispensing with a criminal trial. I said the minister should have discretion over the revocation of citizenship after a criminal trial ... and it reflects very poorly that those quoting me can’t read beyond the few lines they are citing.

“I assume they have been given speaking notes to that effect, but my report does not provide a justification for what they intend to do … it is not what I said, nor what I think now, and anyone who claims otherwise is wrong. In fact I am saying the opposite.



“I doubt many of those citing my report have read beyond the one paragraph they refer to and that does not bode well for mature consideration or lawmaking.



“To say I am not amused would be an understatement.”



A leaked government question time briefing argued that requiring a conviction before the minister was able to exercise the discretion to remove citizenship would render the provision “toothless” and that if a conviction was required most of the dual-national Australians fighting with Isis would retain their citizenship.



“In many cases law enforcement agencies will know an Australian has been fighting with terrorist groups but will be unable to present sufficient eligible evidence to secure a conviction,” the document states.



Prominent constitutional lawyers have agreed the government cannot legally bypass judicial process and give a minister the discretion to take the decision to strip citizenship.



The vice chancellor of the Catholic University, Greg Craven,wrote in the Australian that stripping either dual or sole nationals of citizenship via a ministerial decision “would be irredeemably unconstitutional. By conferring a profoundly judicial power on a minister, it mocks the separation of powers. It would be swatted down like a bug by the high court.



“The possibility of stripping Australian citizenship from a terrorist dual citizen is more plausible, at least provided Australia managed to get in first. But even then the decision would have to lie with a judge, not a politician.”



Craven told Guardian Australia on Tuesday it remained “impossible to have separation of judicial power without judicial power”.



“The government is going to have to be very careful with this or it will become their Sir Robert Menzies moment with the attempt to dissolve the Communist party.”



Abbott has said the new citizenship laws will be introduced during this sitting fortnight, after which the opposition will be provided with briefings and they will be considered by a parliamentary committee.