I saw this female wasp today on ring-barked Sycamore and wonder if this image is enough for an ID to be put on it. On the iSpot site a few days ago*, I posted some other images of what look wasps of the same species, including a male - smaller than the female. I presume these are wasps that are parasitic on larvae within the wood.
* *Insects on a ring-barked Sycamore tree"; "Insects on a ring-barked Sycamore (cont.)" - both to iSpot 10th March, 2014