Sounds like it might be purple salsify, if it is, when the flowers finish it will form a seedhead like a large dandelion 'clock'. Its a biennial with a tap root. If you pull/dig it up before it seeds you shouldn't get any next year. Google 'purple salsify' for some pictures.

If the flowers only last for a single day, then it is certainly what Jaykaty says, salisfy. Personally I love them and a whole area of our garden has become 'naturalised' with them. You can also cut the unopened flower heads and eat them after steaming them from a few minutes.

I didn't know the flowers were edible Bertie, although I was told that in parts of mediterranean europe the roots are eaten. I think they are attractive plants too. I haven't a big enough garden to allow them to naturalise, so I grow some from seed each year.

Roots and flowers are both edible Jaykaty

A big thank-you,yes it certainly is purple salsify.I googled it as you suggested and you were spot on.I will let it seed itself as i quite like it,I don't think I will be eating it though.-joe bell