Tory MPs have rejoiced at today's YouGov/Times poll showing that Ed Miliband is viewed by voters as "less trustworthy, decisive or competent than Gordon Brown". It's worth noting that Miliband is rated as a better leader than Brown by 32 per cent to 17 per cent and that around a third of voters have yet to make up their mind about him (meaning he still has time to win them round) but the numbers are hardly encouraging for a man who hopes to become prime minister in less than two years' time.
The Labour leader's unimpressive personal ratings are one reason why many Conservatives continue to believe that they will be the largest single party after the next election. David Cameron, they point out, has consistently led Miliband as "the best prime minister" in YouGov polling (by 32-21 the last time the question was asked) and has regularly enjoyed a higher net approval rating. By framing the 2015 election as a presidential contest - do you want David Cameron or Ed Miliband as your prime minister? - they hope and believe they can overturn Labour's poll lead.
It's true that Miliband's ratings are a concern for Labour; such figures are frequently a better long-term indicator of the election result than voting intentions. Labour often led the Tories under Neil Kinnock, for instance (sometimes by as much as 24 points), but Kinnock was never rated above John Major as a potential prime minister. More recently, in the 2011 Scottish parliament election, Alex Salmond was ranked above Iain Gray even as Labour led in the polls. The final result, of course, was an SNP majority.
But while Cameron's greater popularity could save the day for the Tories, it is complacent of the party to assume as much. History shows that a well-liked (or, more accurately, less disliked) leader is no guarantee of electoral success. In the final poll before the 1979 election, Jim Callaghan enjoyed a 19-point lead over Margaret Thatcher as "the best prime minister" but that didn't stop the Conservatives winning a majority of 44 seats. Similarly, in the 1970 election, Harold Wilson's personal lead over Ted Heath (a 51 per cent approval rating compared to one of 28 per cent for Heath) didn't stop Labour going down to a decisive defeat.
It's too early to say which precedent 2015 will follow, but the key point is this: there is no reason to assume that Miliband's ratings (should they fail to improve) will cost Labour victory. In the meantime, the Tories would be wise to focus on the potential obstacles to a Conservative win: the surge in support for UKIP (which will almost certainly improve on its 2010 share of 3 per cent), the defection of Lib Dem supporters to Labour in Tory-Labour marginals (the seats that will determine the outcome of the election) and the continuing lack of growth.
In 2010, David Cameron's lead over Gordon Brown wasn't enough to deliver the Tories a majority. In 2015, his lead over Miliband may not be enough to deny Labour victory.