Prime Minister Tony Abbott has sought to explain why a Liberal MP from WA charged taxpayers more than $5,000 for a trip to far north Queensland.

Federal MP Don Randall and his wife travelled to Cairns in November last year for what he said was a trip for "electorate business".

A week later he updated his register of members interests to declare he had bought a four-bedroom investment property in the area.

Speaking on Melbourne's 3AW on Wednesday, Mr Abbott said Mr Randall made the trip to Cairns to have a meeting with then chief Liberal Party whip Warren Entsch.

Mr Randall repaid the cost of the trips after the issue was raised publicly this month, but until now there has been no explanation as to what sort of electorate work he was doing in Cairns.

Mr Abbott scotched suggestions Mr Randall's trip to Cairns was to oversee his investment.

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"The gentleman in question tells me that he didn't do that," he told 3AW.

"He went from Perth to Cairns to have some very important discussions with the whip."

Mr Abbott did not offer details of the conversation, but he did suggest it was not the sort of talk that could have been accomplished with a simple phone call.

"There are certain things that just have to happen face to face," he said.

"Members of Parliament are entitled to travel to have important meetings, because teleconferencing is sometimes no substitute for a face-to-face discussion.

"Now I'm not defending any particular action and look, over the years there have been a lot of things which look contrived I've got to say."

Mr Entsch did not respond to The World Today's requests for an interview.

Meanwhile, taxpayers also paid for the Coalition MP and his wife to fly from Perth to Melbourne on Saturday September 15 last year at a cost of $5,203, for what a Department of Finance document says was "sittings of Parliament".

Parliament sat last year the week before that date and resumed on Monday September 17.

That Saturday night, the West Coast Eagles faced Collingwood in Melbourne in an AFL semi-final.