So, it?s no longer unknown, I have found out what the plant is that I posted here.

So, the plant turns out to be – drumroll please – Nigella, damascena, ?Miss Jekyll?

Nigella is an old cottage garden flower, a favourite for scattering wherever there is a gap in the flower border, but also good for short-term massed bedding and for drying. For many years ‘Miss Jekyll’ was the only widely available variety, and it is still popular for its dependable masses of sky-blue flowers. These last for about eight weeks, and it is worth deadheading or sowing a later batch to extend the season. Sowing in autumn or in March, in a cold frame in paper pots in cold districts, produces early flowers. In windy gardens, support the stems with twiggy sticks.