Its a cornflower (Centaurea)

Thanks very much, Bamboo. Now I realise I grew it from seed but none of the others came up and then it got lost in the general chaos.

General chaos, hmmm, sounds like my life;-)

It's Centaurea Montana which I grow in the garden as it is an old-fashioned plant and I remember my Mother having it (strange how you associate things with plants). Now you have it you probably won't ever be without it as it seeds very easily, so you get lots of free plants. There is a white form which shows up really well against the foliage - when I get a space for it!

Also look out for a variety called 'Amethyst in Snow' which has flowers that are white with a purple centre.