A leading constitutional lawyer believes the Government could lose both of its High Court cases over dual citizenship and the postal vote on same-sex marriage.

The High Court is set to rule on the eligibility of members of parliament caught up in the dual citizenship fiasco – including Deputy Prime Minister Barnaby Joyce.

The High Court is set to examine the cases of seven parliamentarians in October.

Speaking at the National Press Club on Wednesday, dean of the law school at the University of NSW Professor George Williams was not optimistic about the future of the parliamentarians.


The high court will hear two challenges against the postal survey on same sex marriage next week, both of which will argue the $122m price tag for the survey is inappropriate.

Williams said the government could only spend that much if there was an “urgent” and “unforeseen” need.