Liberal MPs scrambled to paper over internal divisions sparked by a leaked email as polls showed the opposition failing to make headway on the Rudd government.

Despite a lukewarm reaction to the federal budget, two polls gave Labor a 57-43 lead over the coalition, with a 70 per cent preferred prime minister rating for Kevin Rudd.

Opposition Leader Brendan Nelson's preferred prime minister rating rose out of single figures, but only just - hitting 12 per cent in a Newspoll and 17 per cent in a Fairfax Nielsen survey.

The polls were taken before a leaked email from treasury spokesman Malcolm Turnbull exposed deep divisions within the Liberals over cutting fuel excise - a major plank of Dr Nelson's budget reply speech.

And a rift emerged between senior South Australian Liberals Alexander Downer and Nick Minchin after Senator Minchin said the former foreign minister was retiring.

Mr Downer on Monday night called for opposition MPs to show "steely discipline" and suggested that Dr Nelson's call for a five-cents-a-litre cut in fuel excise might not be Liberal policy at the 2010 election.

Senator Minchin dismissed his comments in a radio interview.

"Well, Alexander is not on the frontbench and he's retiring," Senator Minchin told ABC Radio, prompting a furious response from Mr Downer who labelled him presumptuous.

"It's a big, big decision for me in my life and I am not going to be harassed or cajoled into making a decision," Mr Downer told Sky News.

The South Australian spat was a skirmish on the sidelines of Dr Nelson's battle with Mr Turnbull over the fuel excise.

Dr Nelson refused to comment on his relationship with Mr Turnbull but made it clear he expects him to toe the coalition line in a major speech on Wednesday.

"Mr Turnbull is doing a very, very effective job," Dr Nelson told reporters.

"Malcolm will be at the press club tomorrow in Canberra.

"He'll be setting out a very strong case as to why the budget of the Rudd government has failed Australians, pulled the plug on pensioners, and importantly that we are the people who stand for lower petrol prices, which will also mean of course lower grocery prices."

But in an email leaked to a national newspaper, Mr Turnbull told Dr Nelson's office that cutting the fuel excise was bad policy and that his objection to it would "inevitably find its way into the media".

Mr Turnbull is also reported to have urged potential leadership rivals, including Joe Hockey and deputy leader Julie Bishop, to move into state politics.

Ms Bishop did not deny that the approach was made but said she had no intention of moving to West Australian politics.

"Look, I don't discuss private conversations with colleagues, but I can make this point, I have no intention of entering state politics," she told ABC radio.

Mr Hockey backed Dr Nelson, comparing him to a diamond being forged under intense pressure.

"I strongly support Brendan Nelson," Mr Hockey told Fairfax radio.

"I tell you what, in some of my darkest moments in politics, people have said to me: 'diamonds are forged under pressure'. And in this sort of situation Brendan Nelson is having huge pressure applied to him as a new leader of the opposition and I think he's coming out stronger."