The Turnbull government faces a testing byelection, risks having ministerial decisions reversed, and has lost its majority, leaving it exposed to challenges to penalty rate cuts and a banking royal commission, after the High Court disqualified five MPs and Senators, including Barnaby Joyce.

Mr Joyce, the Nationals leader, must win back his NSW seat of New England at a December 2 byelection, while his deputy Fiona Nash, who was also disqualified, faces a messy Coalition brawl if she is to fight her way back onto the NSW Senate ticket.