The latest Times/Populus survey  (£) is the most striking poll we've seen for months. It gives Labour a 15-point advantage over the Tories (45 to 30), the largest lead that any pollster has shown for the party in this parliament. If repeated on a uniform swing at a general election, those figures would send Ed Miliband to Downing Street with a majority of 136 seats.
But there's a catch. When asked whether they would rather have Cameron as prime minister or Miliband, just 31 per cent said they wanted the Labour leader, with 60 per cent preferring Cameron (a rise of four per cent since June). Of those who chose Cameron, 23 per cent said this was because they were happy with the job he is doing, while 37 per cent said they were unhappy but still preferred him to Miliband.
But this is a parliamentary system, you say, why should we care? The answer is that personal ratings 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. A more recent example is the 2011 Scottish parliament election, which saw Alex Salmond ranked above Iain Gray even as Labour led in the polls. The final result, of course, was an SNP majority.
By the time of the election, when opposition parties come under greater scrutiny and governments tend to claw back support (as was the case in 2010), the Tories will hope that Cameron's superior personal ratings (if they last) will give them the edge. For all the opprobrium heaped on him by the right, it's a reminder that the PM is still an electoral asset for his party.