Mr Barilaro, appearing at a Independent Commission Against Corruption (ICAC) hearing on Monday, said had he known in 2016 about the secret relationship with Wagga's then-MP, he would have made the Australian Clay Target Association face a competitive grants process.

Partly due to Ms Berejiklian's actions, Mr Barilaro told ICAC, the grant to build The Range function centre in Copland Street was instead given "unusual" and "expedited" approval through the Expenditure Review Committee of Cabinet (ERC).

Mr Barilaro said Ms Berejiklian put the grant on the ERC agenda and told him she supported it.

Counsel assisting ICAC Scott Robertson asked Mr Barilaro about an email he and Ms Berejiklian received from Mr Maguire in July 2017 complaining about a lack of progress on the clay target centre funding with the subject line "here we go around the merry-go-round one more time!"

"That's typical Daryl, in relation to how he approached ministers to chase funding .... he was a pain in the arse, he was a very strong local member, someone who would not let go; like a dog at a bone." Mr Barilaro told ICAC.

Mr Robertson asked Mr Barilaro what he would hypothetically have done differently if he had known about the relationship prior to last year.

"Most of us would have done things differently: the way that the item would have been debated, who would have been in attendance, there would be another approach in terms of dealing with what would be a perceived conflict of interest," Mr Barilaro said.

"I don't believe it would have ended up on the ERC agenda in the first instance, unless there was some probity arrangement around the relationship," Mr Barilaro said.

"If it was on the agenda, I would have assumed the treasurer [Ms Berejiklian] would have left the room during the debate."

ICAC is investigating allegations against Ms Berejiklian that she had a conflict of interest in major grants awarded to Wagga worth a total of $35.5 million while she was in a close personal relationship with Mr Maguire.

Ms Berejiklian has denied any wrongdoing and is due to appear at ICAC on Thursday and Friday, while Mr Maguire is due to appear on Wednesday.

Mr Robertson on Monday asked Mr Barilaro if it was "unusual" to have a single item on the (ERC) worth just $5.5 million.

Mr Barilaro said an item of that size would normally be brought to the ERC as part of a whole budget or large program worth hundreds of million of dollars.

ICAC also published documentation from an ERC decision in 2018 that approved paying $10 million to Property NSW to allow the Riverina Conservatorium of Music to move into the former government building on Simmons Street in Wagga.

The document records Ms Berejiklian as chairing the meeting at a time when she was still in a close personal relationship with Mr Maguire, which was then a secret from her cabinet colleagues.

Mr Barilaro said he felt Ms Berejiklian had less of a potential conflict of interest in the conservatorium as it was presented to the ERC as part of a range of projects, but she still should have declared her relationship.

ICAC revealed last week that the NSW government had cancelled the $20 million stage two funding allocation to build a new recital hall complex at the Riverina Conservatorium of Music's new site at Simmons Street.

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Mr Barilaro confirmed on Monday that he was the one who "signed the briefing that killed the project" this year telling ICAC that the recital hall "unfortunately didn't stack up".

Mr Barilaro said then-premier Ms Berejiklian and then-treasurer Dominic Perrottet approved the $20 million during the 2018 Wagga byelection.

Riverina Conservatorium of Music chairman Andrew Wallace told The Daily Advertiser on Monday that construction work was continuing on stage one of the project to refit the Simmons Street building for musical education.

"The original funding source for the 300-seat recital hall is not going to work but we still have meetings later in the year about stage two and an alternative way of doing it, so it's not dead," Dr Wallace said.

"Stage one and moving in is definitely happening, that money is committed and the site is committed to us and we will be in there by next year ... stage two of clearing the rest of the site and putting in a recital hall is still under negotiation."

The Riverina Conservatorium of Music and the Australian Clay Target Association have not been accused of any wrongdoing.

Under cross examination by Sophie Callan, who is acting for Ms Berejiklian at ICAC, Mr Barilaro said he agreed he received "arms-length" advice from his staff that the Wagga clay target function centre proposal was a benefit to NSW and he should support it, which he did.

Mr Barilaro denied Ms Callan's suggestion that he was influenced by his party's Orange byelection loss the month before the ERC meeting in December 2016.