There was much gloom among the Conservatives recently after a poll  by Lord Ashcroft of their 40 most marginal constituencies showed Labour ahead by 14 points (a larger swing than nationwide) in the 32 seats in which it is in second place. But the pessimists in Cameron's party have been cheered  by some new data reported today. In a piece  on why the Conservatives believe they can win a majority in 2015, Dan Hodges quotes one "Tory analyst" as saying of Ashcroft's poll: "We reran it in the seats we hold but included the name of the sitting MP. We were ahead by 2 per cent."
The bounce, the Tories suggest, is attributable to "incumbency advantage" with sitting MPs benefiting from greater voter loyal than their unelected counterparts. The existence of this effect is not disputed. In 2010, both Tory and Labour incumbents performed disproportionately well. Labour's vote fell by 5.2 per cent in those seats where the incumbent stood again, compared to 7.4 per cent elsewhere, while the Tories' rose by 4.1 per cent in incumbent seats, compared to 2.9 per cent elsewhere. But without seeing the full results of the poll (the wording of the questions, the sample size, the weighting) it's hard to judge its reliability (it is always wise to be sceptical of off-the-record briefings on private polling).
So, it's worth asking, why don't the Tories publish the poll for all to see? Under the rules of the British Polling Council, they may even be forced to do so. As the BPC states , "In the event that the results of a privately commissioned poll are made public by a third party (i.e. external to the organisation that commissioned the survey, its employees and its agents — for example the leak of embargoed research) the survey organisation must place information on its website within two working days in order to place the information that has been released into proper context." Lord Ashcroft, it is safe to say, will be watching closely.