A third Australian government minister has revealed she might have been unlawfully elected to Parliament because of a constitutional ban on dual citizens that has snared six lawmakers since July in an unprecedented political crisis.

Fiona Nash, deputy leader of the Nationals junior coalition party, told the Senate on Thursday she had been advised that she may be British because of her Scottish father.

But Nash said she would not step down as a Cabinet minister until the High Court ruled whether she should be disqualified.

The 116-year-old section of the constitution that bans dual nationals is taking an extraordinary toll on the finely balanced Parliament elected in July last year.