I'm in Herts and I've got the same problem with my espaliere plum tree - the little buggers seem to have munched a hole in just about every plum on the tree (wouldn't mind if they just devoured one or two, but kind of annoying that they're ruining all
of the fruit)
It wasn't until yesterday I even figured out what what causing it, when I caught one in the act! Previously I thought it might be wasps as I'm sure it was those that was plaguing the Discovery apple tree next to it. But now I'm not so sure - there were certainly lots of wasps buzzing around the apple tree and lots caught in my juice jar trap, but was I'm wrongly giving them the blame?
Anyway, what did you mean by soap spray? You mean like washing up liquid in water? It's got to be worth a go if there are no other ideas...