Ely - Stupidly, I cleared the entrances of snow this morning thinking it was the right thing. Fortunately read this thread this morning and returned to the hives to heap some snow on the landing boards. As I arrived I saw a perfectly healthy bee returning, it bounced off the hive and landed in the snow. Then went totally hyper trying to take off again but ended up just leaping around - dead within less than a minute.
I was surprised the cold killed them so quickly.
Judging by the numbers of dead bees lying on top of the snow outside that hive, looks like quite a few suffered the same fate this morning. Lesson learnt.