The next general election was always going to be tight. The latest Populus poll should puncture the autumn election bubble, while providing some home truths for all three main parties.

First, the six to nine-point Labour lead of a month ago has narrowed sharply in the past fortnight to level pegging. The Populus rating of 37 per cent for Labour and 36 per cent for the Tories is in line with two recent polls. The three-point rise in the Liberal Democrats to 18 per cent, at the expense of other parties, down four points at 9 per cent, may partly reflect a change in the way questions are asked (see www.populus.co.uk). But the Lib Dems face the loss of a large number of their MPs.

Second, the Brown bounce has been trimmed, but has not disappeared. Even after the latest shifts, Labour remains nearly five points higher than in the late spring, while the Tories are still more than a point below their preJuly level. David Cameron will be pleased that his counter-attack over crime, Europe and health has boosted Tory ratings, but there is a long way to go. On today’s figures, Labour should win 60 seats more than the Tories, and have a small overall majority of between 10 and 20. But this could easily disappear during a campaign.

Third, a special analysis by Populus of the 120 battleground seats, those with the smallest majorities, is only fractionally better for the Tories than the country as a whole. The three latest monthly polls, all since Gordon Brown took over, have been added together to give a sample of 501 for the 120 marginals. On this basis, Labour support is up 1.1 points since the 2005 election, compared with 1.6 nationally, with the Tories ahead by 1.5 points in the marginals, against 1.1 nationally. There are indications, subject to a much wider margin of error, that the Tories would do better than average in the 60 most marginal seats, and less well in the next 60. This suggests that Labour’s overall majority is vulnerable, but it will be much harder for the Tories to become the largest party.

Fourthly, despite Labour’s decline, Mr Brown’s leader rating (on a scale of 0 to 10) has risen since July from 5.49 to 5.79. Mr Cameron’s rating, by contrast, is flat, at 4.87 against 4.81, near the lowest of his leadership.

Fifth, three out of ten voters, including Tories, believe that Mr Cameron started off by trying to change his party and bring it closer to the centre ground, but recently seems “to have moved back to the Right”. But 38 per cent, including 45 per cent of Tories, still believe that he is sticking to his strategy of changing his party. A quarter of all voters, and of Tories, however, say that he never really tried to change his party.

Sixth, the public is broadly favourable to Mr Brown, but sceptical about what he has achieved. Only 6 per cent believe that he has made a real difference to Britain, 28 per cent only a little difference, and 62 per cent no difference at all. Similarly, 21 per cent say he has done better than expected, and 6 per cent worse, but 67 per cent about as well as expected. And while 39 per cent say that Mr Brown has been action, not words, 46 per cent say that he has been all talk and no action.

So Mr Brown has a lot still to prove to voters. Re-election is far from assured. Do not bet against a hung Parliament.

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