Was doing to gibbing in another part of the house. After checking the wall I determined I would replace a bit and found this bastard in it! A not so fun surprise but there was an obvious gap to be patched.

(Have reported)

What is it?

Looks like a paper wasp nest

Aah ok false alarm then. It looked a bit like hornets nest example on the MPI site. I'd only ever come across the open-celled paper wasp nests to date -

TBH it does look as much like the hornet's embryo nest examples as the paper wasp examples. You can always send them the photo and let the experts review it. I'm sure they would probably prefer that than not hear about a hornet nest.

I did send it through, with a rule for scale - they asked for a pic of the inner core with a ruler. Didnt hear back so will assume it was a wasp (learned something new).

Well that's good news!