The last two YouGov and Ashcroft polls have given the Tories a 4% lead over Labour. Undoubtedly, both of these polls and their results can easily be dismissed as being "Random sample variation", as some other polls continue to have a small Labour lead. As I have mentioned various times throughout the campaign, single polls are simply white noise, and it's the overall trend that actually counts.
In fact, there's another, far more important reason for why these polls are bad news for Labour. In both Ashcroft and YouGov had Labour tied with the Tories...until a turnout filter was applied. The turnout filter reveals Labour's problem. Labour's voters are significantly less likely to be 10/10 certain to vote than Tory voters. Why this is the case is completely uncertain. Perhaps out of a lack of enthusiasm for the party or its leader? Perhaps the answer lies in polling by YouGov, suggesting that the party's supporters are expecting defeat and seem demoralised.
Whatever the answer, it's clear that Ed Miliband and Labour will have to run a very good campaign if they expect to have any chance at all of winning.