We have what seems like an endless supply of wasps just now (free to a good home if anyone would like them?) and I have no idea where they are coming from. They appear 1 or 2 at a time on a couple of windows, but fortunately they're a bit sleepy. We have had nests in the eaves, but they are coming into places with no connection to the eaves (where is Agatha Christie when you need her for a sealed room mystery?) and I'm going about with a rolled-up newspaper for whacking purposes.
Next year we are using one of these repeller things you plug in, and outside we are going to hang up Waspinators (can't do links, just google; they do work) or stuffed plastic/builder's bags all round the place. It will look odd, but perhaps the wasps will go elsewhere.
Apparently they are very useful for pollination and for eating pests in the spring, but become a nuisance when the adults don't need to feed the young any more.