Common Chicory (Cichorium intybus) pops up here and there in the countryside. I had always thought it to be an introduction to these shores but various sources list it as native. Actually I don't think it looks very 'British'. I reckon it drifted in from southern Europe sometime in the distant past.

 Also grown in gardens and probably a garden escape in some locales. An edible herb, ancestor of culinary Chicory.