I'd thought that the buzzing was coming from Bees on a flowering shrub just outside the Pump House door, but I was mistaken; they were inside.
Having 'hoovered' the bottom of the pool, I was just flushing away all the dirt from the filter (backwashing), when I saw a largish swarm of Wasps above the door. They were looking at me with menace in their eyes.
Two of them stung me. One just above my left knee, and the second much higher up on my right leg (ahem). I was of course wearing shorts.
So I taught the little blighters a lesson, and sprayed the nest with Wasp-U-Hate. It seems to have done the job.
As I say almost every other day; "If it ain't one thing it's another!"
And, yes, the stings bloody hurt.