Opposition Leader Peter Dutton says Prime Minister Anthony Albanese has “trashed his reputation” for a political fix by reneging on his commitment to the stage 3 tax cuts.

Mr Dutton said the prime minister’s motivation was fear of a loss in the Dunkley by-election that would be a significant blow to his leadership.

“I think the prime minister has decided that he wants the political fix for Dunkley. I don’t think that’s disputable. I think it’s absolutely the case that they’ve made a political decision,” the opposition leader told 7.30.

Mr Dutton said the Coalition was supporting the government’s tax cuts to help Australian families, not the prime minister.

“We’re supporting taxpayers who were doing it tough,” he told 7.30.

“We support it on the basis, not of supporting his lie, but of supporting families who are hurting as a result of bad decisions he [the prime minister] has made.”

Pressed on whether his support signalled the government’s policy had merit, Mr Dutton again took aim at Mr Albanese’s integrity, describing the overhaul as a “significant broken promise”.

“I don’t think the prime minister will recover his credibility. I think the Australian public look at him in a very different way.”

In parliament this week, the opposition questioned the timing of Treasury’s advice on stage 3 tax cuts.

Treasurer Jim Chalmers confirmed Treasury began preparing advice on measures to address the cost-of-living crisis in December.

Treasury deputy secretary Dianne Brown told a Senate committee earlier this week that it was Treasury’s decision to recommend changes to the stage 3 tax cuts.

The prime minister maintains the advice was only finalised a week before the change was approved and formally announced, saying it was a “difficult decision but it was a good decision.”

Dutton attacks ABC culture

In an at-times tense exchange, Mr Dutton also criticised the ABC’s coverage of tax reform, claiming it was biased.

“It’s such an ABC perspective, if I might say, all the culture that’s so far-left within the ABC just seems to permeate through many questions when you go on a program like this.”

Mr Dutton also rejected a comment made by former prime minister Malcolm Turnbull on the ABC’s program Nemesis when he referred to Mr Dutton as “a thug”.

“It was a fabrication and it was a self-serving comment. But I don’t think anyone’s scared of ghosts, I think everyone moves on,” he said.

“And I think, frankly, the Australian public is so moved on from that era.”

Mr Dutton said that the Coalition was now united: “more so than any opposition in recent history on either side of politics.”