There is an open window in the attic which they weren’t aware of. They live in an old Victorian house and couldn’t see the window from the ground!
Well done on getting the picture on Kay, something a bit bigger than wasps then! Off to have a Google, will come back in a while. Agree with Alan, Crow, Rook, Raven or could be Pigeon or Collar Dove, but us sure if they would build indoors, but looks like their type of nest.