At this time of year generally bees and other insects take advantage of the good periods amongst the changeable weather, particularly favouring sunny periods and warmer weather even when these are short. I have seen activity around my cherry today, so I hope this is occurring elsewhere as well - otherwise there might be some bad crops!
I think the trees are hardier and less fussy overall than the insects, and if there is bad weather whilst the blossom is out it is not good news for fruiting prospects. I think greengage is especially vulnerable, since it flowers earlier.