Malcolm Roberts's election may have been invalid, government solicitor tells court

Barnaby Joyce rival Tony Windsor given permission to join citizenship proceedings set down to return to high court on 10 October

Malcolm Roberts could be the exception among sitting parliamentarians ensnared in the dual citizen saga in that his election in 2016 may have been invalid, the high court has heard.

Roberts and former senator Scott Ludlam were different to the other three politicians so far referred to the high court - Barnaby Joyce, Larissa Waters and Matt Canavan - because they knew they had been citizens of other countries, the solicitor-general, Stephen Donaghue, told the court on Thursday.