The damaging leak of a Malcolm Turnbull email criticising Brendan Nelson’s 5c per litre fuel excise reduction was a deliberate ploy by Turnbull … that’s what the Nelson camp believes.

Turnbull has denied having anything to do with the leak of the email to The Australian’s Glenn Milne.

“Neither I, nor anyone acting on my behalf, disclosed the existence or the contents of the correspondence,” Turnbull declared this morning.

But sources close to Nelson believe Turnbull deliberately released the email to undercut his leader, who was finally gaining some positive media coverage following his budget reply.

While the 5c-a-litre proposal has been damned by economists and the serious commentariat, talkback response has been positive, providing Nelson with the critical “cut-through” that he has been lacking since becoming leader. The Nelson camp believes this has prompted Turnbull to deliberately undermine Nelson by leaking an email critical of the proposal, sent to Nelson Chief of Staff Peter Hendy late at night last week.

Nelson’s office certainly had no interest in leaking the email, and Crikey understands there has been no third-party access to the email at Nelson’s end. That leaves Turnbull and his office as the only credible source.

The leaking is regarded as particularly treacherous given Turnbull – contrary to denials in Milne’s article – made a strong argument during budget reply preparations for a 10c-a-litre excise reduction. Turnbull’s argument was no mere hypothetical about the political impact of the Nelson idea he argued that a 10c reduction would be far more effective than Nelson’s limited 5c proposal.

The leak has wrecked the Opposition’s first positive media weekend since the carer’s issue and taken pressure off the Government, which is under increasing scrutiny over the “alcopops” and private health insurance issues. Insiders say Turnbull doesn’t care.

“He is brilliant, but erratic, and totally egocentric,” said one.

“This is a man who called John Howard on the way to his concession speech on election night to tell him how well he’d done in Wentworth.”

It comes on top of Turnbull’s poor performance in response to the budget last week, after being wrong-footed by the Government’s “tough as all hell” rhetoric.

The leak may also bring the Nelson-Turnbull endgame forward, just when everyone had relaxed into assuming Nelson would be around for a while yet. If the allegations are true, it suggests an element of Keating/Howard style obsession to Turnbull’s bomb-throwing, a willingness to inflict damage on his own party to pursue his own leadership ambitions. It’s a pretty shabby look at the moment, and can’t have won Turnbull any recruits to his cause.

However, just like the Liberals did with Howard in 1985 and Labor with Keating in 1991, the party may eventually conclude that Turnbull should be given his go rather than be allowed to continue wrecking the party, and be permitted to implode or, alternatively, succeed brilliantly.

A key problem, however, is that if Turnbull fails as leader, he won’t be sticking around to help pick up the pieces. Turnbull’s long-term commitment is to himself, rather than the party he hopes to lead, and in any event he has never persisted in one career more than a few years.

All of this may also encourage more MPs to try to convince Peter Costello – whose antics last week suggested he had already mentally left the building – to take on the leadership. That won’t solve the Turnbull problem, especially as Costello knows all about ambitious deputies, unless the party made it clear that Turnbull would have to wait. As today’s revelation suggests, Turnbull isn’t one for waiting.