Windsor joins High Court citizenship fray

Former independent MP Tony Windsor has been granted leave to join the High Court dual citizen fight over his political rival Barnaby Joyce.

Mr Joyce is one of several politicians referred to Australia's highest court after it was revealed they did not meet the sole citizenship requirement of section 44 of the constitution.

The deputy prime minister and Nationals party leader renounced his New Zealand citizenship on August 12 after it was discovered he had inherited the status from his father.

James Joyce was born in New Zealand while it was still a British dominion and moved to Australia in 1947.

When the status of New Zealand citizenship was created in 1949, James was granted it retrospectively and passed it onto his Australian-born son without his knowledge.

Solicitor-General Stephen Donaghue QC told the High Court on Thursday there was a "clear demarcation line" between the politicians - those who had known they were a citizen of a foreign power and those who did not.

Mr Joyce falls into the latter category and could escape disqualification because it was less reasonable for him to renounce any ties to other countries.

Mr Windsor lost the seat of New England to Mr Joyce in 2016 after a bitter and tight election battle.

He was the only third-party to be granted leave to take part in the proceeding against a politician other than the politician themselves and the Attorney-General.

The court heard Mr Windsor's lawyer will also seek to cross-examine Mr Joyce as to what steps he and the Nationals party took to check his eligibility to stand for parliament.

Mr Joyce's case, which also includes senators Scott Ludlam, Larissa Waters, Matt Canavan and Malcolm Roberts, will be heard in the High Court in Canberra between October 10 and 12.