However, despite looking in my butterfly book, and on one or two lepidopterous websites, I was unable to identify him. What I did find, though, was Matt's European Butterflies, a really beautiful website, with an invitation to e-mail. So I sent said Matt the photo, and, Bob's yer butterfly, the very next day he was able to inform me that what I had was a lackey moth caterpillar. Lackey moths are little brown jobs, very unremarkable, but their caterpillars are rather fine, as can be seen, with cute blue and black googly 'eyes'.
So thanks Matt!