A Nationals MP says claims their Coalition partners the Liberals tricked them into accepting an increase in the fuel tax will only make the Nationals more "bolshie" in the future.

One MP, who did not want to be named, told the ABC about half a dozen nationals MPs are "pissed off" by news the Liberals duped their National Party colleagues into thinking the Government was seriously considering reducing the diesel fuel rebate.

Senior Liberal sources told the ABC they were never serious about cutting the diesel fuel rebate, boasting it was a tactic to "play the Nats" so the party would support the higher fuel excise as the lesser of two evils.

The measure to reduce the rebate would have been vehemently opposed by the powerful mining lobby as well as the fishing and farming sectors.

Publicly, the Nationals are strongly denying any suggestion they were outplayed.

But privately many concede it is possible they may have been deceived.

"About half a dozen of us believe it's probably true and we're pissed off," said the MP.

"The main thing is its going to make us more bolshie.

"If they thought we were bolshie on ADM [the American agribusiness which wanted to buy Graincorp], wait until the next fight."

Treasurer Joe Hockey and his Finance Minister Mathias Cormann have rejected the report as "complete unmitigated rubbish".

"I don’t know how many different ways to say the story on the ABC is wrong, it never happened," the Treasurer told journalists at Parliament House.

Senator Cormann backed the Treasurer's denial, saying the story was a "complete fabrication".

Their Cabinet colleague and Nationals MP Barnaby Joyce says he takes them at their word.

"We're not fools, we go around and I talk to senior Cabinet ministers and all of us come to one clear statement: this conversation never happened," Senator Joyce told reporters at Parliament House.

"Nobody who would know says it ever happened.

"I believe Joe Hockey; I think he is a trustworthy person. If he said it didn't happen, it didn't happen.

"Ultimately in any relationship you work on trust because without trust you have nothing."

Nationals 'caught with their moleskins down' says Labor

But Nationals backbencher Andrew Broad agreed his party had a "long history" with the Liberals.

"Skulduggery in politics, is that a news story, really?" he said.

Shadow treasurer Chris Bowen said the Government was "scrambling and in damage control" by denying the reports.

"Senior Liberal members of this government boasting that they'd lied and tricked members of their own Government," he said.

"If the National Party can't trust the Liberal Party, how can the Australian people ever trust the Liberal Party?"

Shadow agriculture minister Joel Fitzgibbon said the Nationals had been "caught with their moleskins down".