To a much greater extent than is generally acknowledged we use events to justify conclusions that we were already minded to reach. When David Cameron's bicycle was stolen in Notting Hill this week, the media represented him sympathetically as an ordinary guy doing the shopping, and sharing - albeit involuntarily - the grief that crime causes his fellow citizens.

If Gordon Brown's bike had been nicked in identical circumstances we would have dubbed him a prat for chaining it to a stub from which it could be easily lifted, and described the incident as yet another stumble for a hapless politician who seems incapable even of taking his bike down to the shops. Apparently objective facts can be arranged to point in quite various directions.

And so, in the Glasgow East by-election, a couple of hundred votes one way rather than the other tipped the balance towards a result that we are ready to pronounce “devastating”. Yet those few hundred votes - that narrow defeat - weren't what is important. A narrow Labour victory would have pointed equally to a horrible outcome for Gordon Brown's administration in any nationwide election, confirming what the polls have been showing for months - that the Government is unpopular and heading for defeat at the next election.

For Labour the by-election has simply clothed in flesh a problem that was hanging in the air. The loss of Glasgow East is a cipher for deeper anxieties - and, just possibly, an excuse for the party to grab its fate by the collar and ask the question that it shrank from asking a year ago: does it really trust Gordon Brown to lead Labour into the next election?

Will Labour face or duck that question? Among MPs and sympathisers whom I talk to there seem to be three opinions: 1. Carry on regardless; 2. Postpone the decision until after the party conference in the autumn; or 3. Start the ball rolling to replace the leader now.

The real choice is between 1 and 3. To postpone the decision until autumn is a cop-out, a cloak for doing nothing. Next autumn equals never.

If in its heart the party wants to carry on regardless, that's fine. There are occasions in history when hammering on and hoping for the best has paid dividends. Paralysis is a respectable option.

But Labour MPs, trade unionists and grassroots members should not delude themselves that waiting until the autumn is some kind of a third way between action and inaction. Unless Labour goes into the autumn conference minded to use it to remove the leader, he will survive it. And after the Christmas and new year holiday of 2008-09, the case for ejecting him before a disastrous general election does that job for the party begins to fade.

I can see it already. Mr Brown has an awkward conference with the trade unions in Warwick this weekend, but no serious move is made against him. Charles Clarke and a handful of ultra-Blairites mutter on into the end of July - but they are not the stuff of which a leadership challenge is made.

As for those Young Turks and old reliables who might challenge Mr Brown, they prick up their ears and are seen in restaurants, but nobody wants to wield the knife.

Then it's the summer holidays. As these draw to a close and journalists and their ministerial dining-companions come back from the olive groves and beaches, there begins a rising murmur that Labour's September conference in Manchester is “make or break” for Mr Brown.

Can't you just hear the clichés roll? His leadership is “on trial”. His job is “on the line”. He has to make “the speech of his life” this year. “The knives will be out” for him if he stumbles.

Then comes the conference. Each supposed leadership contender's speech is fingered excitedly to see if a potential bid is in prospect; listened to intently and pronounced afterwards as containing (perhaps) some hint of ambition, but in no sense a declaration. Finally Mr Brown speaks. He isn't particularly good (he never will be) but he doesn't fall flat on his face either. He has had all summer to write this speech.

And then what? Did this “make” or “break” him? Hardly. His critics continue to grumble, his palace guard pronounce him victorious, and the great mass of his MPs and followers sighs a little disappointedly, but realises that there's nothing here to get their teeth into.

A bottle of champagne, then, for the first reader to spot - before me - the commentator or Labour politician this October declaring that the party has the winter holidays, now, to think about the leadership, and that (say) the European elections next year will be the “crunch point” for Mr Brown.

Two bottles of champagne if it's the same politician or commentator who wrote that Glasgow East was to be the crunch point.

People reluctant to get a grip on difficult decisions and who wait for fate to offer them handles often wait for ever, and often secretly want to. The choice facing Labour this summer (the party will moan) is invidious.

But actually it isn't. They're lucky. Most administrations, as they approach the end of their natural shelf-life, become disliked as administrations - their leadership disliked, but no more or less than all the rest of the team.

To become more popular there is no simple change in personnel that they can make - nothing big they can fix.

Labour is more fortunate this July. There is something it can fix. Mr Brown. The party knows - and it infuriates them - that Mr Cameron is more vulnerable than he seems. Few in Labour think that winning the next election is likely, but giving Mr Cameron a good fight is perfectly imaginable.

Polls tell them that much of the electorate's anxiety about this Government is focused on a single personality - its leader.

Unfair as this may be, it gives the party the opportunity to remove at a stroke what most obviously irks the voters. Let's be candid about this: it would be to make Mr Brown a scapegoat, and that's unfair. But scapegoat is a role, I fear, that he would play with distinction. The honeymoon that followed his departure might not last long, but it should be sufficient to pull the party back to an honorable defeat at the general election, which a new leader would be admired for calling promptly.

For Labour, victory next time is hardly likely, but the difference between honorable defeat and total wipeout lies not just in the scores of Labour seats involved, but in the morale and energy of the incoming Principal Opposition whose task it would be face up to a new Tory government in its critical and maybe hesitant first months. That would be the very worst time for a Labour civil war about direction and leadership.

Whoever may challenge Mr Brown for the crown therefore has a tricky task in the art of communication. He or she must essentially be saying this to potential supporters: “I cannot promise to win the next election for you, but I can mitigate the rout.”

Oddly enough, for me as a former MP that does resonate. It might resonate better than you think among the Parliamentary Labour Party.

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