Can you just block up the hole in the wall, Ian?
Also, wasps take a mental snapshot when they leave the nest and thats how they recognise the place when they return.
Apparently, there are these wasps that live underground and would fly out through a hole, circle around and take a snap of the area and fly off. Some scientists observing this moved everything around the hole around two inches to the left and when the wasp came back, it slammed into the ground two inches to the left of the hole.
Maybe if you rearrange your garden after they all leave, the wasps will be confused and move on. Or you could recreate your garden in your neighbours garden and all of the wasps would move next door.
Hope this helps.
how much money would you have to be given to put a wasp up your hole?