Political life might have turned out very differently for Malcolm Turnbull if a plan hatched by Scott Morrison when Mr Morrison was Liberal party state director had been implemented.

The plan would have parachuted Mr Turnbull into the NSW upper house to take over the position of state opposition leader, with a switch to a safe lower house seat after an election.

The plan, confirmed by Mr Morrison in an interview for Good Weekend, was sketched out in early 2002 as a "Plan B" if then NSW opposition leader Kerry Chikarovski – up against a seemingly impregnable Bob Carr – had faltered in the run up to the 2003 state election.

But the plan was abandoned after the NSW party made a surprise decision to dump Ms Chikarovski and elect a then 33-year-old John Brogden in her place.

Mr Morrison, who delivers his first budget on Tuesday, told Good Weekend that the Turnbull-for-NSW plan was "not very advanced. I don't think either of us [himself or Turnbull] thought it was going to go anywhere. I mean Kerry was Plan A, and I was very committed to Plan A".

Mr Morrison's unhappiness about the switch to Mr Brogden was known to senior Liberals at the time, though the Treasurer insists he regarded Mr Brogden as a "brilliant campaigner".

Of recent strains in his relationship with the Prime Minister, Mr Morrison says "Malcolm and I have a longstanding friendship that survives all the normal exchanges you would expect between PMs and treasurers. I would go further and say that the strength of our relationship coming into these roles would be greater than that of any of our counterparts over the last 20 years or so.

"That does not mean we have always agreed on everything. It's not surprising that there will be tensions from time to time between prime ministers and treasurers, But we have a reservoir of a relationship to drawn on to move through all of that."

Mr Morrison's preselection for the seat of Cook in 2007 was turbulent, and occurred after the party abandoned the originally anointed candidate, right-winger Michael Towke, and ran a second preselection contest in which Mr Towke alleges he came under extraordinary pressure from the party hierarchy to withdraw. Good Weekend can reveal the existence of a secret legal deed signed between Mr Towke and then state director Graham Jaeschke​ in which Mr Towke (who'd been bombarded with allegations questioning his fitness to stand) agreed not to recontest the preselection in return for having his good name restored. Mr Towke says he was also offered a job in Mr Morrison's office – though Mr Morrison denies this.

Former state MP Marie Ficarra​ said what was done to Mr Towke was "unjust and unfair", and demonstrated why the party should move to plebiscites for preselections.

"Preselections based on factional warlords' control of party branches have to come to an end [to ensure] that what happened to Michael Towke will never happen to anyone else," she said.