Defecting senator Cory Bernardi has told Malcolm Turnbull that his 2015 leadership coup against Tony Abbott is a key factor behind his decision to quit the Liberal Party and start his own conservative movement.

The soon-to-be former Liberal senator formally informed the Prime Minister of his intentions in a phone call on Tuesday morning, after details of the move were first revealed by Fairfax Media on Monday. Senator Bernardi has now formally resigned from the party, ahead of an expected address to the Senate after midday.

According to sources, Mr Turnbull asked Senator Bernardi the reasons for his departure just seven months after being re-elected for a six-year term to represent the Liberal Party in South Australia. Senator Bernardi replied he would explain his reasons to the public on Tuesday.

Ominously, Senator Bernardi warned Mr Turnbull that moves were afoot to displace him because of his own poor performance in the polls – a reason the Prime Minister used to justify his 2015 move against Mr Abbott.