In my favourite Brer Rabbit story, our eponymous hero calls on Mr Fox to do literally anything - barbecue him, drown him, skin him alive... whatever - except inflict upon him the horror of being thrown into the briar patch. Fox accordingly throws bunny into brambles. Bunny dives straight for hidden burrow. Escapes.

Next week, as Thursday's by-election cheers and boos subside, Brer Cameron and his crew will be calling on Gordon Brown to do literally anything - make way for a Conservative Government, hold an early election, precipitate a leadership contest, resign... whatever - except inflict upon us the horror of two more years of his wretched administration.

The moral is clear. For Mr Brown to carry on regardless is the Opposition's bramble patch. There lies their burrow. There lie their best hopes for a whopping victory after a general election that they've had ample time to prepare for. To those Labour sympathisers who call for the party to regain its composure and carry its sickly leader through two more years of power, I reply that this is exactly what David Cameron hopes for too.

As an observer, albeit Tory, who tries, however fitfully, to present a fair picture to his readers, I can see as clear as daylight what the Parliamentary Labour Party must do to save their party and its still-needed influence on British history. It must fight the next general election beneath the banner of a leader in whom it is possible to believe. That person is not Gordon Brown.

A general election in 2010, which the Government had long despaired of winning and in which the whole country regarded the Labour leader as a lame duck whom his party had feebly decided to dispatch after rather than before the election, could prove an absolute wipe-out. A 2010 general election where the governing party had panicked at the last moment and changed its leader in a death-bed conversion to the obvious, would bring Labour into total public contempt. Yet, to my bafflement, it is towards one of these two alternatives that the PLP seem to be marching.

Understand - I concede this at once - that I have no real feel for the culture of the Labour tribe; but accept that I have some idea how Tories think. And come with me, Government MPs, into the minds of David Cameron and his frontbench team. Look through their eyes at the scene that confronts them - you lot, on the benches opposite - and ask yourselves where in the long term they see advantage. You do know, I think, that Mr Cameron has steady nerves. What would an opposition leader with steady nerves be aiming for, if not the prolonged, hard-pounding, two-year destruction of an incompetently led Labour Government's morale, self-belief and national standing? Mr Brown is there for bayoneting practice, until the Tory troops are ready.

Isn't this obvious? Can't you see why thinking Tories want the present administration to limp wretchedly on for as long as our constitution allows under a leader who has lost beyond retrieval the respect and the affection of the electorate; and then to go down to a dreadful defeat in 2010 - hit so hard they don't get up again for a decade? Don't you sense how relaxed is the centre right at the possibility that Mr Brown will be given more rope - two years' supply - before his party hangs itself? Don't you smell a whiff of nervousness on the Right that Labour might, finally and after all, throw itself from a bus speeding towards the abyss and pick itself up with a new Leader who understands how to fight Tories? Why, Labour MPs, would you positively opt for the agony of a leadership in its death throes being played out slowly in a long, cruel, humbling spectacle, before the eyes of the whole country and its news media?

Euthanasia has always been more tolerantly viewed on the Left than the Right - so why choose for your own leader the lingering death and the saline drip? But there's another reason, beyond the avoidance of Labour's slow humiliation, for its MPs, trades unions and members to trigger change.

By soldiering on under a stumbling high-command, the party is giving the Tories time to rearm, and giving the voters time to get used to the idea of a Conservative government- in-waiting. As importantly, this government-in-waiting is winning the time to get used to the idea that a government-in-waiting really is what they are.

They are being offered two more years to work up a programme for government, get the sums right, the ideas clear, the manifesto written and the message strong. Already - haven't you noticed? - they are starting to walk and talk like an incoming leadership. And when an opposition leader and his team see themselves as ready to take power, the rest of us read the body language, sense the subliminal confidence and start to see them that way too. Why give them two more years to grow?

As of the end of May 2008, the Conservative Party is beatable. I doubt it would be the likelihood, but it would be worth Labour's aiming for. A stronger possibility is that a powerful Labour counter-attack now could knock the Tory advance off balance and pin them back to their more core support base. In any ensuing general election they could then be held to a much narrower victory than looks likely on the present poll figures.

They could also be flustered into offering a dishonestly rosy prospectus for government, renouncing in advance the bolder of their ideas for public service reform, and making silly promises about generous future future spending.

The consequence after such an election would be a narrower parliamentary arithmetic in which 50 or more Labour MPs who on present trends look likely to lose their seats, keep them: a post-election Commons in which a new Conservative government had a slim majority, no real mandate for right-wing reform, and an unrealistic manifesto that began to fall apart from Day One.

To lead a pre-election fightback that could deliver this, Labour must be commanded by someone who understands Tories and their ideas; who gets the logic of their political philosophy - and so can see how patchy and confused is the Shadow Cabinet's effort so far to translate instincts into policy. Blinded by hatred of the Right, Brown doesn't begin to understand what Tories (or indeed the English) are about. Yet sitting behind Cameron and Co at Prime Minister's Questions are a dozen of his own side who could pull their own manifesto mercilessly apart, if they wanted to; and who understand what a tentative, vulnerable, breakable and confused creature the Parliamentary Conservative Party - as of May 2008 - still is.

It is into such minds that a successful Labour leader must enter. To paraphrase Disraeli, a Labour Prime Minister in 2008 surveys on the front bench opposite him a row of par-baked baps. By 2010, and with two more years to be compared with Gordon Brown, they'll be tough cookies.

The message to Labour is clear. Get another leader and go soon.

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