After a bit of research, that is, Google, I discovered that it is a Paysandisia archon or Palm Moth. According to Wikipedia:
andIt is native to Uruguay and central Argentina and has been accidentally introduced to Europe, where it is spreading rapidly.
There are no palm trees in our gardenthe species is causing increasing concern in Europe because of the sometimes fatal damage being caused to native and exotic palms.
![Very Happy :D](./images/smilies/icon_biggrin.gif)
I don't think that this particular specimen is much of a threat though, as it seemed to be very worn, and was still in the same place nearly two hours later when I took this photo:
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Colin