The High Court would probably strike down a plan to automatically revoke dual nationals' citizenship, a leading constitutional law expert says, with solicitors already gearing up to challenge it if it becomes law.

UNSW professor George Williams told a Senate inquiry on Tuesday that it was the most "problematically drafted bill" he had ever seen, with more constitutional problems in it than any he had given evidence on. This included a law that allows ASIO to detain and question any Australian for up to a week and foreign fighter legislation aiming to restrain Australians returning from conflict zones in Syria and Iraq.

Professor Williams had "no doubt" such a law would be challenged in the High Court and had already been approached by "prominent solicitors" who had clients facing charges that are included in the bill.

"It's such an obvious one to bring a challenge to; I don't see why they wouldn't to escape loss of their citizenship."



Under the plan, crimes that could automatically deprive you of your citizenship range from treachery, sabotage and mutiny to damaging or destroying Commonwealth property. Dual nationals engaged in terrorism-related activity would automatically forfeit their Australian citizenship even without a conviction, though they could appeal the revocation in court.