Either the electorate's mood is unusually volatile, or some pollsters are in trouble. The same researcher which last week trumpeted a 12-point poll lead for the SNP found, over the past week, that Labour is three points ahead.

As these polls, carried out by Scottish Opinion, are the two most recent published, it leaves the election campaign further open than anyone had thought.

On constituency vote intentions, Labour had 35% support, the SNP 32%, LibDems 15%, the Tories 13% and others 5%. On the regional vote, Labour had 34% support, with the SNP on 31%, LibDems 13%, Tories on 12%, Greens 5% and others scoring 5%.

Part of the reasoning may be that polls continue to find high numbers of undecided Scots. An mruk research survey carried out for The Herald at the end of March found 50% of voters were undecided, and of them two-thirds were either certain or very likely to vote. That poll was the only other one to put Labour ahead, but it was not alone in finding voters unwilling to commit.

For Labour, the pattern may be good news. It acknowledges its traditional support base is soft - reluctant to turn out to vote because they are put off by any number of issues at Westminster or at Holyrood. Labour's tactic is to repeat that of the past two elections, creating terror among its supporters at the prospect of an Alex Salmond SNP government. With such a prospect now very realistic, Labour's scarifying is cranked up.

That is why yesterday's poll suggesting the SNP might be slipping is not all good news for Team Labour. Spin doctors are doing nothing to dispel the impression that Labour may get cuffed.

The polls matter more than ever in this campaign, as they have been the key source of the dominant narrative of a two-horse race with the SNP ahead.

Nationalists need the polls to keep momentum. As with any team sport, when things begin to go your way, everything tends to slot into place and more things go right. They need to keep polls buoyant.

Meanwhile, Labour has given the impression of being out of luck, with only one game plan, and a poor response to its rivals' tactics. When things start going wrong, they slide further. The team gets fractious. Players prepare to dodge the blame.

Sunday newspapers featured stories of a Labour election broadcast tonight featuring party hacks posing as ordinary punters.

The SNP hopes this will undermine Labour's credibility, while Labour hopes the publicity only draws attention to the broadcast's message about SNP tax bills.

There are rumours - none reliable - that opinions are shifting over Labour in its west central heartlands, and that Labour's safest seats may shift to Nationalist.

There is talk not only of disillusion with Labour but real hostility. Yet some of that talk comes from Labour.

So between conflicting polls, the high numbers of undecided voters and the convoluted spin and bluff, the intriguing, close-fought election campaign makes the result even harder to call.