Thanks for the replies so far on this. I do mean cm and not mm but Leith,my wife, thinks that I may have exaggerated the size
. But I still think that they were over a foot long, so perhaps 30-50cm. Going through the books I did think of butterbur but the habitat seemed wrong, they were at the base of the cliffs in a very exposed position.
I wonder if they are perhaps not a native but some sort of exotic that has been washed or blown in?
Thanks, Pete