"jmbillings" wrote
I should have clarified, I am indeed in the UK. The names I mentioned
were what came up on various sites I found; however I can understand
the confusion as many of the sites seemed to be American.

I've just looked up Cirsium palustre and it has some similarities to
what I saw, but the site he
http://www.dgsgardening.btinternet.co.uk/marshthis.htm
says it doesn't have spines on the surface of the leaves, which I'm
sure the one I saw did. In addition, the photo doesn't quite compare
as the one I saw was more of one tall stem with the leaves coming off
on shorter "branches" rather than the one there.

Your description reminded me of teasels, which can grow very tall. They
have quite spiky stems and leaves and look rather thistle-like. I don't
suppose it could have been that?

http://wildseed.co.uk/species/view/46

--
Sue