[Chrissie2]

Thanks Geoff - I think those may be a bit too small at 15 -19 mm. Mine was at least 35 mm long and its body appeared to be longer than the wings when the latter were close to the body. I probably won't see it again this year, but will aim to get a photo next year if it materialises again.

Thanks to everyone for your input. I really appreciate your efforts in trying to help me identify this seemingly gentle giant.