Unless, British scientists have cunningly developed a new species of bees, I'd venture a wild guess that what you are experiencing are not bees. I've been a bee keeper here in the U.S. for a number of years and will vouch for the fact that bees only congregate in hives if they are domesticated bees. I suppose you could have a wild bees nest but that is rarely around human habitation and would most likely bee quite large but hidden in a dead tree or some such. I would expect that you may be experiencing some other insect, but if you are observing the nest and if it's a grey, papery looking affair that's semi-circular in shape, you most likely have some variety of wasp... being a non- native to your fair isle, I wouldn't know what variety with which you are plagued. But here's what they look like:
http://www.bugwise.net.au/guide/wasps
Wasps do like water, whereas bees, although attracted to it aren't as agressive in pursuing a source. like what you're seeing. If, on the off chance they do happen to be bees, try hanging a bird type waterer near their nest. Move slowly, wear white or light colored clothing and they shouldn't bother you... don't swat at them! The waterer doens't need to be all that close, but closer than your holey wall.
Be careful, since wasps or hornets can be very agressive, at least until you determine exactly what they are...