A parliamentary inquiry has revealed that when NSW Premier Dominic Perrottet was treasurer he asked to examine the candidates for the UK agent-general role even though someone had already been selected.

The Upper House inquiry into the controversial appointment of former deputy premier John Barilaro as the US senior trade and investment commissioner (STIC) resumed today and is now also examining the state's other overseas postings.

Paul Webster, the current trade and investment commissioner to the UK and Europe, gave evidence from London.

He was originally deemed the preferred candidate for the agent-general role in 2020, but the job ended up going to Stephen Cartwright, who was a late entry to the process.

Emails obtained by the Upper House and referred to during the inquiry show the external recruitment firm hired by the government to conduct the search concluded the process in December 2020 and recommended Mr Webster.

His appointment had to be endorsed, and the emails reveal an attempt to set up a meeting between Mr Webster and then-treasurer Mr Perrottet before subsequent meetings with the then-trade minister John Barilaro and then-premier Gladys Berejiklian.

But in an email dated January 25, 2021, a staffer from Mr Perrottet's office stalled that process.

The staffer said before an "e-meeting" could be scheduled with Mr Webster, the treasurer wanted to see a candidate short list.

"The Treasurer has requested a 'short list' of other candidates that were interviewed, together with a copy of their resume," the email read.

"When the info is available, could you please send to me and I'll forward to the treasurer for his attention."

The inquiry has previously heard that a month after the email was sent by Mr Perrottet's staffer, Mr Cartwright applied for the job after a conversation with Mr Barilaro.

Today Mr Perrottet denied knowing that the independent recruitment process had recommended Mr Webster for the job.

"I don't believe I was advised that Paul Webster was the preferred candidate," the premier said.

Mr Perrottet has previously been adamant he had nothing to do with the recruitment of the agent-general position.

Mr Webster told the inquiry he never met with Mr Perrottet or Mr Barilaro.

While he didn't get the agent-general job, he was appointed by the state to be the trade and Investment commissioner in London.

A report commissioned by Mr Perrottet into Mr Barilaro's appointment to the lucrative New York job found the process was not at "arm's length" from the government and noted possible breaches of ethical conduct.

Mr Perrottet said that review made it clear the recruitment process was "flawed" and announced tighter rules about when former ministers could apply for public sector roles.

Mr Cartwright is scheduled to give evidence to the inquiry on Wednesday.