The wife and kids are off to the folk's caravan for a few nights this week, so I'll get foam and powder. They are getting in a small gap in the bricks into the eves of the garage and also in a couple of the mortar gaps between the wall and barge boards. (Only 6" apart) I suspect the nest is in the eves (certainly can't see it inside).
They are pretty quiet in the late evening. I assume foam is better where you can see the nest - but it can be sprayed from 2m away, which gives me time to leg it. The powder would mean getting up step ladders (only about 2 steps though) then puffing it - how much time do you think I'll need before dashing for it.....?