As I'm not much of a botanist, I am struggling to identify this plant which grows in abundance along the river Cherwell in Oxford:
Young leaves look like this:
I now think it's Common Hogweed - also see the German Wikipedia entry which has better pictures - according to those, all details seem to match. But all expert botanist advice welcome.
Oh, and I'm also clueless about the insects that often crawl around on it, as in the photo above, but the plant is more important as my son is obsessed with it and I was worried that it might be poisonous (I found half a dozen similar looking plants that are poisonous, in fact).