On poll movements

This morning's YouGov poll for the Sun again showed a Labour lead of seven points - CON 32%, LAB 39, LDEM 11%, UKIP 13% (that's Tuesday MORNING'S poll, btw, Tuesday evening's isn't out yet!). Five of YouGov's last six polls have shown single figure Labour leads, whereas previously the average Labour had been consistently around 10 or 11 points. Put in the context of the falling Labour leads from ICM, MORI and Opinium it is pretty undeniable that something is afoot.

YouGov's average figures in the first half of April were CON 31%, LAB 41%, LD 11%, UKIP 11% The average over those last six polls is CON 32%, LAB 40%, LDEM 11%, UKIP 12%

So roughly speaking we appear to have had a small increase for the Tories, a slight knock for Labour. At this point we can normally expect lots of speculation about what has caused it... or more typically, lots of people claiming that the thing they personally care deeply about has caused it, the thing they think their party shouldn't be doing has damaged them, or the thing they think their party should be doing has helped them. Normally such claims don't bother with evidence.

The harsh truth is that we usually can't really tell what has caused a movement in the polls. Sometimes there is an obvious event that coincides with a big shift in the polls which, while it doesn't prove anything,

does strongly imply a connection (after all, we can't be sure that the big drop in Tory support in March last year was definitely due to the budget, but it would be a remarkable co-incidence if it wasn't!). Other times there are all sorts of plausible explanations.

The most obvious explanations for the current narrowing relate to Margaret Thatcher's funeral. That could impact the polls in terms of lots of positive retrospectives about Thatcher in the media... or could have an indirect effect in the sense that it interupted the normal flow of politics. David Cameron got to spend a week or two looking statesmanlike without the normal dirty business of politics and governing. However one could equally look at other underlying factors, the welfare debate for example, perhaps a generally more focused presentation by the government since Lynton Crosby returned, some figures from the Blair era apparently criticising Ed Miliband. All these things add up.

My own working assumption is still that is it is a Thatcher effect of one sort or another that will fade away, but it really is impossible to know. We shall have to wait and see if it lasts.

UPDATE: The Sun Politics team have tweeted tonight's results - CON 33%, LAB 40%, LD 10%, UKIP 12%