Gordon Brown and Labour were in political trouble before the Glenrothes victory, and they still are today. The difference is in morale and mood. Neither should be ignored. Labour leaders believe that they now have a fighting chance, and there is a big difference between a 1997-scale rout and a hung parliament. But the odds against a fourth term still remain very high, not least because the recession has yet really to bite.

A bounce, however real, is not the same as a full-blown recovery. So forget talk about an early general election.

First, the positives. Raising your share of the vote, by three points to 55 per cent, as Lindsay Roy, the new MP, did is very rare for a governing party in any by-election. Labour has done this only once in 11 previous contests in this parliament. So Glenrothes is a very good result by any standards.

The outcome is a personal coup for Mr Brown, and not least his wife Sarah, after their unusually close involvement. It cements a good few weeks for Mr Brown. This began with his decisive handling of the banking crisis and what now looks like a shrewd reshuffle five weeks ago, which ended talk of a leadership challenge and healed internal party divisions. Blairite critics were silenced. Together, these have boosted Mr Brown's self-confidence and his party's morale. Both are in striking contrast to the fatalistic mood only just over three months ago after Labour's big defeat at Glasgow East.

Secondly, the caveats. Several specifically Scottish factors favoured Labour, and these will not be repeated in England. The party was able to run an effective anti-incumbent campaign against the SNP, which runs Scotland and the local council.

That tactic is not available in England. The Tories are largely irrelevant in Scotland but not south of the Border. Moreover, the SNP has been on the defensive over the banking crisis.

So how firm is the Brown bounce? It exists but is limited. Labour is no longer in freefall and its ratings have picked up since the summer. Labour averaged 28 per cent in all polls between the March Budget and the start of the banking crisis in September. Since then its rating has been 31.5 per cent but this increase has been largely at the expense of the Liberal Democrats and other parties. The Tories' average rating has slipped only from 43.5 to 42.5 per cent.

Polls tell only part of the story. There has been a widespread sense, not least within the Tory party, that David Cameron and his team have been adrift, having little distinctive to say about the financial crisis and the recession.

Yet the Brown team is rightly cautious. The recession is going to get worse before there are even any faint signs of recovery. That could mean a rough ride next year, notably in June's local and European elections. But this autumn Mr Brown has secured his position as Prime Minister and gained time, and freedom of manoeuvre: a respite but probably no more.

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