I'm guessing they've played a good part in it - although it's always been the case that if you:
a) have colder air aloft (850s are a few degrees below average at the moment) and
b) can get rid of the sun
...then you can get some unusually low maxima in summer, or late spring. There was that late May spell in 2006, for example, with single-figure maxima widely across southern England, caused by the sun being blotted out by thick cloud. The thing is it's really very hard to get a whole day down here from May to July where the sun is blocked throughout - it's a good 16 hours or so of cloud that you need!
When it does happen, though, the results can be amazing. Indeed, I'd wager it's the only way to get highs that are 8C or more below average for the time of year in May to July (and probably August too).
Originally Posted by: Retron