Barry O'Farrell was meant to be standing at Tony Abbott's side as the prime minister announced billions of dollars in road funding for western Sydney.

Instead, the NSW premier sent Mr Abbott a text on Wednesday morning to tell him that not only would he not be making it to Liverpool, he was resigning his job.

Despite being thoroughly overshadowed, Mr Abbott used his press conference to launch an unprompted defence of his Liberal colleague and friend.

Mr O'Farrell had "innocently" and "inadvertently" misled a corruption inquiry, he told reporters.

The premier had done the "utterly honourable" thing by stepping down.

"We are seeing an act of integrity and an act of honour," he said.

Mr Abbott admonished a reporter who queried whether he could still trust partnering the "corrupt" NSW government on his roads plan.

That was an "entirely unjustified smear", he said.

The prime minister said public figures met lots of people who gave them many things - from pens to ties to wine.

So it was reasonable to expect a bottle of vintage wine could be forgotten.

"Given that premiers and other senior politicians have very crowded busy lives, I don't think it is reasonable to expect everything from some years ago to be front of mind," Mr Abbott said.

Mr Abbott said he had no recollection of ever meeting Nick Di Girolamo, whose evidence to the corruption inquiry led to the premier's decision.

But he could not say he had never met the Sydney businessman.

Source: The Daily Telegraph. Original article.