UK polling report analysis
http://ukpollingreport.co.uk/
They do tend to know what they're talking about.
//As ever, the more unusual a polls findings the more careful you should be – it could be a sign of UKIP support collapsing back towards the Conservatives, or could just be sample error. In YouGov’s polls over the last month we have seen some hints of a narrowing of the Lab lead and signs of UKIP support fading, and ICM do tend to show the lowest levels of UKIP support and relatively low Lab leads – all the same it looks quite odd. I would wait and see if it is repeated in other polls before getting too over-excited.
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I'd go with that analysis
+ people tend to feel better about things when the weather's good, they're looking forward to holidays which favours the party in power