Possibly one of the Aster family? I have one which spreads like mad and looks similar, but there are a variety of plants that look similar. Someone will know.

Sweet Willam? (Dianthus barbatus if you're a latin names enthusiast)

Thank you both.I don't remember planting it but that dosn't mean I didn't! Anyway will see what happens.

it also looks a bit like a penstemon.

Let us know when the flower buds appear - that will clinch it.

I have just noticed that there are clumps of this which end have popped up all over.Just hoping it's not something which I should be removing.

Id say penstemon too, doesn't normally self seed as far as I know, not in my garden anyway.

just realised the photo is upside down.

it could be one of the willow herbs especially if it is appearing in other places. another possibility is evening primrose.