We can start getting serious about opinion polls showing Labor comfortably in front when the next round of Liberal leadership speculation begins.

The subject has been off the agenda since Peter Costello accepted that John Howard would not be retiring, but there’s no-one like a back bencher fearful of losing to bring it back again.

For the moment, Liberals in marginal seats continue to believe in the invincibility of their great election winner. A Newspoll like today’s — putting Labor in front 56 to 44 in terms of the two party preferred vote eight months before the scheduled polling day — is not enough to dent their confidence.

But let there be three or four more in a row showing similar figures and the speculation about changing Howard for Costello will surely begin. Watch for it.

Just as backbench Liberals don’t believe the polls, neither do their Labor counterparts. The idea that Howard is some kind of super campaigner is as ingrained in the opposition as it is in the government.

While there is a greater sense of anticipation in the Labor troops as the parliamentary year begins, there’s no sign yet of the smugness which would help Howard begin a revival in his fortunes.

Peter Costello, meanwhile, has had a quiet summer break with few appearances in the media. He has accepted not just that Kevin Rudd will have a honeymoon period but that Malcolm Turnbull will as well.

The Treasurer will wisely continue to sit back and wait to see how his short and long-term opponents for the top job handle the task of removing the Labor lead.