Laws that automatically strip citizenship from Australians who engage in terrorism must be “urgently” repealed, the independent authority on national security legislation has recommended.

Under current laws, any dual national who fights for or serves a terrorist group automatically loses their citizenship, even before a conviction in court.

In a report to Attorney-General Christian Porter, Independent National Security Legislation Monitor James Renwick SC said the law should be “retrospectively repealed” for anyone it had already applied to.

“It is neither necessary, nor is it proportionate to the counter-terrorism threat, to revoke such citizenship without considering what the public interest requires,” Dr Renwick wrote.

Because stripping a foreign fighter’s citizenship does not depend on a conviction or administrative decision, Dr Renwick said it leaves intelligence agencies in an uncertain position.

He warned the provision could, in fact, weaken Australia’s national security.

“(The laws) cause confusion and potential legal difficulties for (spy agencies) … (and) may impede criminal prosecutions or cause them to fail,” he wrote.

“The provision does not depend on the Commonwealth or any other person knowing about the conduct.”

Earlier this week, Australia’s lead spy agency, the Australian Security Intelligence Organisation, warned the laws could increase the global threat of terrorism.

“In a globally interconnected world, the location of an individual offshore as a result of citizenship cessation will not eliminate any direct threat they pose to Australian (or other) interests overseas,” an ASIO submission to the inquiry said.

Former monitor Bret Walker SC, who first challenged the provision when it was introduced in 2015, said because of the “arbitrary” nature of the laws, it was impossible to know who has been affected.

“As we speak, we couldn’t possibly say how many former Australians have lost their citizenship by operation of these provisions, we simply don’t know,” he said.

“It is a very strange situation, and James Renwick has spelled it out very effectively as to just how strange.”

In his report, Dr Renwick recommended instead that a ministerial decision ought to be made to actually revoke a person’s citizenship, and that decision be subject to judicial review.

Shadow attorney-general Mark Dreyfus agreed that the laws needed to be replaced.

“This report … does show why national security law can’t be left to Peter Dutton, why it’s vital that we have proper time to consider national security legislation every time that it’s presented,” Mr Dreyfus said.

Minister for Home Affairs Peter Dutton has been contacted for comment.

-AAP