Julia Banks has parted ways with the Liberal party and will sit on the crossbench, undercutting Scott Morrison’s efforts to stabilise the government and project a plan for the next election.

The Victorian Liberal, who has been signalling she might run as an independent at the next federal election since the August leadership implosion, told parliament on Tuesday she would shift to the crossbench – delivering her statement at the same time Morrison was attempting to plot the Coalition’s way forward.

In simultaneous announcements, Morrison told reporters the government would deliver “a surplus budget” on 2 April, confirming his plans for a May 2019 election – and Banks delivered her bombshell in the chamber.