EDMONTON -- A day after calling on the Alberta government to explain a Jason Kenney aide's pricey trips to London, the opposition NDP says it will request an audit of what it calls a "growing scandal."

NDP ethics and democracy critic Heather Sweet spoke to media Thursday, presenting a letter signed by her, finance critic Shannon Phillips and energy critic Irfan Sabir.

The letter calls on Auditor General Doug Wylie to investigate the expenses of Kenney's principal adviser David Knight Legg.

"I will be asking the Auditor General to be doing a performance review on all of the financials and public dollars that this premier is spending, to make sure Albertans are getting the best use of their taxpayers with a good return," Sweet said Thursday.

A day earlier, Sweet said Knight Legg has spent $45,000 of taxpayer money since he was appointed six months ago, including more than $18,000 on four trips to London.

The UCP responded by saying Knight Legg's trips fell within government guidelines and that he was working to bring business to Alberta.

The government declined to disclose the names of any companies involved due to the "commercially sensitive nature" of the meetings "and the fact that foreign-funded activist groups are actively targeting Alberta and large companies doing business in our province."

Sweet said it was unusual for the government not to publicly disclose a trade mission or its cost ahead of time.

"It was first about investment and meeting with bankers in London, and then it became about the war room, and then it became not about the war room, it's just about us not wanting to be transparent and tell you what he was actually up to," said Sweet. "We asked the Auditor General to look into this and make some recommendations for this premier about how to be accountable to Albertans."'

She said the key issue is whether the money spent on the trips to London created a "good return" on taxpayer money.

The premier's office issued a statement in response to Sweet's request for an audit, again reiterating the government's stance that such trips help bolster investment in the province and are necessary because of a "coordinated misinformation campaign" driving investors away.

"We make no apologies for fighting to bring investment back to Alberta and forcibly fighting this foreign-funded campaign of defamation against our province," a spokesman said. "The NDP's strategy of apology and appeasement failed Albertans. Today's latest stunt by the NDP again shows that they do not take defending our province seriously."

The NDP's allegations of misspending came just weeks after NDP Leader Rachel Notley criticized Kenney for spending more than $16,000 on a charter flight for him and Conservative premiers from Saskatchewan and New Brunswick in the summer.