It may just be one poll, but this morning's ComRes/Independent survey putting Labour 8 points ahead of the Conservatives is a big boost for Ed Miliband. The poll puts Labour up 2 points to 42 per cent, with the Tories down 2 points to 34 per cent and the Lib Dems unchanged on 12 per cent.
The 8-point lead is the largest Labour has recorded since 2007 and the Tories haven't been as low as 34 per cent since May.
While support for the Lib Dems has plummeted since the general election (to as little as 7 per cent), support for the Tories has remained surprisingly robust, until now. With Labour also likely to triumph in the Oldham East and Saddleworth by-election on Thursday, Miliband will win some of the breathing space he needs.
Should the Conservatives either outperform or underperform expectations, Cameron will come under pressure. If the Tories do worse than expected in the by-election, he will be attacked for giving the Lib Dems a virtual free ride. If they do better than expected, he will be attacked for missing out on a seat the Tories could have won (they were just 2,413 votes behind Labour at the general election).
Tory high command wories that if it goes soft on the banks the numbers will get worse. Those who have pressed the coalition and specifically the Chancellor to speak out against banker-bashing are told each time that the coalition has to keep public attitudes in mind. Mr Osborne believes voters loathe the banks and blame them for the financial crisis.
Despite his status as one of the least electorally successful Tory prime ministers in history, Cameron has come under little pressure since the election. Instead, it is Nick Clegg and Ed Miliband who have attracted the greatest media criticism. But if, as seems likely, the Conservatives enter a period of sustained unpopularity, the narrative could soon change.