And it's all because former treasurer Peter Costello refuses to declare his hand, despite polls overwhelmingly declaring he is far more acceptable to voters than Brendan Nelson.

Costello, he of the caustic tongue and wit who can cut the best of them to the quick, was one of Parliament's best performers and would be a formidable opponent for Kevin Rudd.

So what's happened to Costello? Is he still sulking because John Howard refused to pass the prime ministerial baton his way before last November's federal election shellacking, or is he really undecided about whether or not he wants to be Opposition leader?

The answer is "don't know", simply because Costello refuses to tell the Australian public, or even his own party, his plans for the future.

We're told Costello will reveal all next month when he finally releases a book about his political life. And while that's all good publicity for Costello's book launch, it's not a good look for the Coalition, which continues to perform poorly.

It's time Costello made up his mind. If he doesn't want the leadership he should say so immediately and get out of politics altogether.