For weeks, Westminster watchers, tea-leaf readers, pollsters and pundits have been predicting that Manchester would be the final scene in the Shakespearean tragedy of Gordon Brown. The plotters would have summoned up enough nerve and the daggers would go in back, front and sideways, leaving the corpse of the Brown premiership.

The plot has been bungled, the conspirators remain (at least, in public) a disaffected and dithering few and the Prime Minister will leave the conference with his skin intact, apart from a few pin-pricks. The soothsayers were wrong all along and there will be no major move against the leader – yet.

They said Brown would have to make the speech of his life to survive. Word from within the Brown bunker is that it will be "the most powerful and stirring he has ever made". Yet, whether it proves to be magnificent or merely adequate, Manchester was never going to be the finally decisive occasion it was built up to be. The battle for Brown's survival will be fought on his home ground in Fife.

Defeat in the Glenrothes by-election would really mean the end. Ministers would troop into Number 10, as Maggie Thatcher's Cabinet did, to tell him if he could not win a by-election in his own backyard, he has no hope of winning the next general election. Brown might try to shrug it off as another mid-term hiccup but resignations would follow.

Those Cabinet colleagues talk in code. Though they appeared to back Brown last week, it was hardly whole-hearted. You do not need the Enigma machine to decipher the real meaning of James Purnell: "MPs are entitled to do anything they want to." Or John Hutton: "My colleagues are right to say that the Government needs to do better."

The enormity of the economic crisis has put Labour's petty-minded internal feuding into perspective. The 'Blair-faced assassins' have backed off and the discontent at ministerial and MP levels has dampened. Voters regard as shallow and selfish politicians who indulge in spiteful squabbles while families and the most vulnerable become increasingly desperate about day-to-day living.

Above all, the 'Anybody But Brown' brigade fail to realise the real truth: Gordon Brown's future is Labour's future. A full-scale leadership contest would become even bitchier and bloodier than the skirmishing we have already seen. The nation would not accept a new leader becoming PM without a general election, which would mean certain disaster with the latest poll showing the Tories on 52%, 28 points ahead of Labour.

The sensible strategy is for Labour to keep Brown and spend the next 18 months exposing David Cameron's appeal as the emperor's new clothes, disguising the fact that the Tories are policy-naked. Brown's former strategy adviser Spencer Livermore, who left Downing Street this year, says that instead of presenting it as a straight choice between the two parties, "we must make the next election a referendum on Cameron's Conservative party".

Cameron and Co must already be quaking with fear at the new campaigning organisation, Go Fourth – Campaign for a Labour Fourth Term. It has been formed, whether Brown likes it or not, by the Fearsome Four – John Prescott, Alastair Campbell, Dick Caborn (you may well ask "who?") and Glenys Kinnock – and its main aims are to "proudly defend the record of the Labour Government since 1997".

Brown may be in need of all the help he can get, but if that lot are his best hope, he is in worse trouble than we thought. And, while these starry-eyed idealists search for the mythical fourth term, there is a more immediate problem in Glenrothes.

Labour's 10,664 majority has already been written off; the 14.5% swing the SNP need is easily achievable after the 22% of Glasgow East; Labour's own canvassing predicts an SNP majority as high as 5,000; and the bookies make the Nats 9-2 on favourites with Labour 3-1 also-rans.

However, Labour's chances have been boosted by the selection of a charismatic candidate in Lindsay Roy, a high-achieving headmaster with a wealth of goodwill in the community. Focus groups carried out by Labour pollsters in the last few days have thrown up deep discontent with the SNP-led administration in Fife (their candidate is the council leader Peter Grant) who have imposed severe cuts in education and social services. In Roy's own school, Kirkcaldy High, the cuts amounted to £101,000 and across Fife school auxiliaries, toilet attendants and attendance officers have been reduced. One result has been an increase in daytime vandalism as truants are left to their own devices.

Labour will attempt to turn the by-election from a referendum on Brown into a referendum on the SNP's broken promises and record in power, locally and at Holyrood. The same focus groups have shown sympathy for Brown, not just as a local lad but as a PM whom many Fifers believe is unfairly carrying the can for events beyond any leader's control.

Why should Glenrothes be any different from the succession of by-election disasters which have dogged Brown? Because it is Fife and, as we Fifers know, the folk there are thrawn and determinedly out-of-step. Not much on which to hang the fate of a Prime Minister and the future of a political party, but these days any straw will do.