NSW Opposition Leader John Robertson says Barry O’Farrell’s resignation isn’t just about a bottle of expensive wine.

NSW Opposition Leader John Robertson says Barry O’Farrell’s shock resignation proves the Liberal Party let lobbyists into the heart of government.

Mr O’Farrell announced on Wednesday he was resigning as premier after learning Independent Commission Against Corruption investigators had a thank you note signed by him and addressed to Liberal fundraiser Nick Di Girolamo for a $3000 bottle of Grange.

It came after he denied to the corruption watchdog that he had received the expensive bottle of red.

But Mr Robertson said Mr O’Farrell’s decision to fall on his sword wasn’t just about a bottle of expensive wine, and pointed to larger corruption issues within the NSW Liberal Party.

“What we see today is not about a bottle of wine,” he told reporters.

“Today is an insight into how the Liberal Party operates in NSW.”

“They have allowed donors and lobbyists to get involved in the public administration of this state.”

Public confidence in the state’s politicians had been “rocked to the core” by the premier’s actions in what was a “very sad day for the people of NSW”, Mr Robertson said.

Asked if he would follow Mr O’Farrell’s lead if his failure to report a $3 million bribe from Michael McGurk in the sale of union property Currawong was found to be inadequate, Mr Robertson said they were “very different matters”.

“We are talking about a government before ICAC – not some kangaroo court that’s been set up in the Legislative Council,” he said.