Depends on the campanula - some get 18 inches, some only 4 inches.

18 inches. Blimey , don't tell my nettle leafed one that, it is already over a metre tall.

Okay, okay, Owdboggy, I know some get even taller, I was just making the point in answer to the question, lol!

Would not mind, but it is grwoing all over the garden as well. It is a seed weed almost as bad as Geranium phaeum or Aquilegias.

Nettle leafed one - no, nothing coming to mind, which one is it, Owdboggy?

Called it that cos my brain is not working at present

The leaves of campanula punctata are a bit nettly I think, but mine doesn't grow as tall as 1 metre

No, it is Campanula trachelium

Never heard of it, so just googled - its common name is apparently Bats in the Belfry, lol