It’s tricky being Prime Minister, I guess. It certainly seems to be tricky if your name is Gordon Brown. Some 15 months ago – finding himself momentarily up in the polls as the nation breathed a collective sigh of relief that His Manicness, Mr Tony Blair, was no more – he dithered about whether to call an election. The result: he plunged in the polls to the point where it seemed inevitable he would be imminently evicted from Number 10.

One financial tsunami later, and Gordon’s off life-support, and is being allowed to convalesce at Number 10 while the nation holds its collective breath lest the merest sigh should send the global economy toppling off its precarious perch. The result: Gordon is once again being forced to ponder every Prime Minister’s dread, prerogative question – should I stay, or should I go to the country?

True, all the polls, without exception, continue to show Labour trailing the Tories; but trailing them by a lot less than they were even three months ago. Although it now seems certain that a snap general election in February has been ruled out – and even the June 2009 option favoured by Mr Brown’s erstwhile aide Charlie Whelan seems to be unlikely – the Prime Minister must still devote precious time, time which could be better spent saving the world, to thinking through The Big Question. What a waste of intellectual energy.

It’s an oddity of Prime Ministers’ legacies that their success is, inevitably, judged in part by posterity’s verdict on whether they got the timing right. Think of Edward Heath, who squandered his Tory Government’s healthy majority, by prematurely agitating for a fresh mandate in February 1974. Or think of James Callaghan, who signed his own minority Labour Government’s death warrant, by clinging on to the reins of power throughout the Winter of Discontent until forced out of office in May 1979.

Their achievements in power – and there were some – were tarnished by their falls from power. Messrs Heath and Callaghan’s very personal decisions to call, or not call, an election when they did led to their being blamed by their respective parties for the defeats that ensued. Whatever else President George W. Bush’s party may say about him, they cannot pin on him the blame for this year’s US Presidential election being held at the worst possible time for the Republicans.

So, though there are many good reasons why opposition parties are right to fear the Prime Ministerial prerogative to ‘cut and run’ when it suits the government, it’s as well to recall those whose careers have been terminated thanks to their unfortunate mis-calculations. It says a lot about Gordon Brown’s Weltenschaung that I’m sure it’s those examples of failure which keep him awake at night, wracked by self-doubt.

* You can find out more about the Campaign for Fixed-Term Parliaments here, and you can read about Lib Dem MP David Howarth’s attempts to change the law – blocked by both Labour and Tory front-benches – here.