We saw several of them growing under the trees, the only plant that they bore any resemblance to was the garden Delphinium.
STOP PRESS - the answer is found. Inge suggested a Campanula, and I have searched all the many varieties of which there are over 500 species. I found the answer on a website here photographed in the exact same pine forest on the Makarska Riviera, Croatia as mine. It is called a Campanula PYRAMIDALIS
On this photo it is possible to see how thick the stem is even towards the top of the plant.
At the top of the plant the stem becomes quite slender.
I have done this 'mock up' of a brussel sprout stem. Hopefully it will give some indication as to the size and robustness of the stem at its base which I neglected to photograph .