London rent 'horrified' chief on $600,000

A public servant paid $180,000 more than the NSW premier was "horrified" by the cost of rent and school fees in London and entered fraught negotiations with public servants for extra perks on top of his salary after arriving in the UK.

NSW Agent-General to London Stephen Cartwright says he quickly realised his $600,000 salary package would not be enough for him to live in the UK capital.

"I started to do some of that research as soon as I arrived and was pretty horrified with what I saw," Mr Cartwright told a parliamentary inquiry on Tuesday.

"I got over here and found out the outrageous rents that you have to pay here, the school fees, that are double anything that you would ever pay in Australia.

"I discovered just how poorly NSW had structured these things."

Mr Cartwright's appointment to the lucrative trade position is being scrutinised after it emerged he sought a salary of $800,000 - almost double the initial offering - and landed the role despite being ranked below other candidates.

The inquiry stems from the controversial appointment of former deputy premier John Barilaro as the senior trade and investment commissioner to the Americas in June, a $500,000-a-year role he resigned from within two weeks.

The former Business NSW executive previously said he met Mr Barilaro for coffee before applying for the role, but rejected assertions his appointment was a case of "jobs for mates".

After tense and protracted contract negotiations, Mr Cartwright eventually accepted a base salary of $487,000 with $113,000 in perks, earning more than the state's five other trade commissioners.

In February, a month after he arrived in London, the state also agreed to pay his rent, expected to cost taxpayers about $105,000.

By June, Mr Cartwright began emailing NSW CEO Amy Brown requesting financial help for his children's school fees.

In July, staffers from NSW Treasury referred to another former Investment NSW staffer Jenny West being upset and in a "real tizz" after a call with Mr Cartwright.

Mr Cartwright told the inquiry he did not recall what had caused the issue.

Multiple emails show Mr Cartwright citing conversations and verbal agreements he had reached with former Trade Minister Stuart Ayres, as he discussed having his contract amended.

Mr Cartwright said in hindsight he understood that citing the advice of ministers during negotiations had caused a bit of a "storm".

But he formed a view that after 30 years without executive representation in overseas trade, the government was not rolling out the trade positions equitably.

"Investment NSW wasn't really sure how to do a lot of these things," he told the inquiry.

Mr Cartwright now stands to save more than $100,000 on UK taxes - a bill which will be picked up by NSW, committee member and Labor MP Daniel Mookhey said on Tuesday.

"Most people would struggle to understand why (Mr Cartwright) was so aggrieved about his package, given $600,000 a year is a very generous salary, according to anyone's standards," Mr Mookhey added.

Premier Dominic Perrottet's chief-of-staff Bran Black also appeared at the inquiry, and disputed evidence given at a previous hearing by Ms Brown, where she claimed he told her to give Mr Cartwright whatever he wanted.

"She was nervous about losing that (preferred) candidate, and the basis for those nerves was that he was asking for a salary that could not be paid," he said.

After benchmarking with others in similar roles, Mr Black suggested Mr Cartwright could be offered a salary package of about $400,000 with performance incentive of $200,000.

"I stressed to her that that was just an idea, because I didn't know what was appropriate and I had no experience in relation to these matters," he added.

The premier has previously defended Mr Black, saying his understanding of what occurred did not match with Ms Brown's evidence.

AAP has contacted Mr Ayres for comment.