and I came home and looked it up in a book. It's name is Chicorium intybus
otherwise known as chicory. It is truly blue and to my untutored eye looked like a dandelion dipped in a paintpot. Blanched stems are meant to be a delicacy - produced by excluding light in the same way that rhubarb can be forced. Having examined the stems, that sounds like too much of a palaver. A substitute for coffee and popular during the second world war. Since there is no submarine blockade these days, I shall stick to the lavazza. To get the coffee sensation, dig up and roast the roots. There will be a knock-on benefit to the health of your liver.
Chicory was introduced from North America in the 17 century. It has long escaped the garden and naturalises on chalky soils.