Ivy is a major late crop for bees. There is a lot available around Oxford and the bees love it.
The problem for bee keepers is that the Ivy honey sets very hard and doesn't taste nice. The taste is not much of a problem because the honey won't spin out in an extractor but the hard set makes it less useful in Winter for the bees.
Honey which sets releases water during crystallisation which can ferment inside the cell. Apparently the fermented liquid can give the bees Dysentry.
The bees have to work quite hard to clear out crystallised honey from cells. I frequently find sugar crystals on the hive floor which have been laboriously excavated by worker bees.