My first guess would be these http://rhs.org.uk/advice/profile?pid=698 - if not, can you post us a photograph please?
Ah, you beat me to it, and yes, Soloman's Seal Sawfly larvae as in the link.
Thanks! Had trouble posting the pics at first but that looks like them. If they were something more pleasant I'd have left them but I think they can come off!
Have you or the neighbours got any chickens? They'd love them
You need to inspect and remove these sawfly larvae every day once you notice them - they are voracious and will completely defoliate the plants if left. They are very, very good at hiding!
Thanks! I've removed as many as I can find and I'll try and get out there every day.