The mother of all sawflies!

Yesterday I found this amazing insect whilst searching for orchids in my meadow. It was very dopey either through age, or the low temperature. As luck would have it, it was still there this morning so I was able to get a few more shots to help identify it.
I've narrowed it down to 2 species, either Large Alder Sawfly (Cimbex connatus), or Large Willow Sawfly (Cimbex luteus). Both are rare in the UK. In 1997 the former was almost declared extinct but it seems to have rallied round a little. The latter is now probable rarer than the former. Something just as rare would appear to be sawfly experts. I'm hoping that a sawfly county recorder from Wiltshire can help.
Both sawflies are, as is obvious from the picture, excellent hornet mimics but lack its formidable sting. Their bark is worse than their bite, although with impressive jaws, I wouldn't want to get a nip from one!