Former Liberal Party leader John Hewson has urged Prime Minister Malcolm Turnbull to give his predecessor, Tony Abbott, a formal role in the federal election campaign to avoid disunity within the Coalition.

Mr Abbott said at the weekend he would campaign with colleagues in marginal seats when asked to do so, even though the Liberal Party has not organised an official role for him.

Mr Abbott has sought to defend his legacy over recent weeks, including giving a media interview on the day Mr Turnbull announced his plans for a double dissolution election.

Mr Abbott said he would be proud to campaign for the Turnbull government because it is seeking re-election largely on his government's policies - a claim that forced Mr Turnbull to explain the "continuity and change" between his government and Mr Abbott's.