YouGov/Sun - 40/42/10
When yesterday's YouGov poll for the Sunday Times showed a two point Labour lead I gave my normal cautious "might yet just be margin of error, wait till tomorrow" type reaction. Well, today's YouGov voting intention poll for the Sun has voting intentions of CON 40%, LAB 42%, LDEM 10%, suggesting that Labour have indeed moved ahead. That said, I expect we will still see the parties swapping the lead back and forth between each other until Labour establish a larger lead (or until the Conservatives get back into a bigger lead).
As to what the reasons for the movement are, whenever there are movements in the polls people jump in to say "Oh, it's because of this or that or whatever", and the this or that or whatever is normally things the person talking finds particularly objectionable or welcome, and hence they'd like to think the movement in the polls is a result of it.
In this case the timings line up with the tuition fee protests, so one possible explanation is that it highlighted an unpopular policy or crystalised disatisfaction on that front. However, it's easy to over analyse the timings of these things and Labour moving ahead could just as well be the continuation of the slow upwards trend in Labour support we've seen over recent months, the slow, culmulative drip-drip-drip effect of cuts.
