An impulse purchase is how Health Minister Sussan Ley is explaining her decision to buy an apartment during a taxpayer-funded trip to the Gold Coast in 2015.

Key points: Sussan Ley under pressure from Opposition over property she purchased in May 2015

Sussan Ley under pressure from Opposition over property she purchased in May 2015 Purchase "was not planned nor anticipated," a spokesperson for Ms Ley says

Purchase "was not planned nor anticipated," a spokesperson for Ms Ley says Labor MP Catherine King is calling for Ms Ley to explain further or hand in her resignation

Ms Ley is under pressure from the Opposition over the property she purchased in May 2015 while travelling to Queensland on ministerial business, accompanied by her partner — whose expenses were also covered by the taxpayer.

A spokesperson for Ms Ley said the purchase of the almost $800,000 property "was not planned nor anticipated".

In a statement, the spokesperson said the Minister had travelled to Brisbane to announce health funding before meeting with "local health stakeholders" 80 kilometres away on the Gold Coast.

"Minister Ley's partner was invited to accompany her to a function in Sydney on the Friday evening," the statement read.

"He then travelled with the Minister to Queensland under family travel arrangements.

"The EMB [Entitlements Management Branch] was consulted at the time to confirm Ms Ley's partner's travel was within the rules.

"All travel undertaken was in accordance with the rules."

The property is described as an investment in Ms Ley's Register of Interests, where she also declares a mortgage for the property.

Ley 'has some explaining to do'

Deputy Prime Minister Barnaby Joyce defended Ms Ley, telling the ABC that she had "legitimate business" on the Gold Coast.

"If they [Ms Ley and her partner] made a purchase — even though I admit it's a substantial purchase — that is not the reason she went to the Gold Coast," he said.

"She went to the Gold Coast for work ... people are saying she concocted a reason to do a policy announcement on the Gold Coast. I think that is a bit rich."

But Labor MP Catherine King is calling for Ms Ley to explain further or hand in her resignation.

Ms King told the ABC that the Minister should also release her diary for the period.

"I think she's got some explaining to do, to explain how purchasing a luxury apartment with her [partner] is in any way, shape or form official business," she said.

"Frankly, if she can't, she needs to resign."

Ms King said while it remains unclear if Ms Ley broke any parliamentary rules, the purchase and its claimed nature did not pass the pub test.

"In anyone's world, $700,000 plus is a lot of money," she said.

"I don't know too many people who would spent that sort of money, even if they had it, on an impulse. It's a pretty unbelievable claim."

Ms Ley had the fourth highest expenditure during the period of the purchase — from January 1 to June 30, 2015 — including more than $105,000 on charter flights and $11,800 on family travel costs.

In total, she claimed almost $650,000 over the six-month period and $490,637 in the following six months.

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