Silene fimbriata

Very pretty...
Is this a perennial ?

It is lovely Wagger...it reminds me of the Bladder Campion with a frilly edge....:o)

Yes, Terra - a bit of a thug, spreading underground like Lysimachia - I'm always digging it back. The flowers are so dainty though. It was one of Roy Lancaster's picks at Chelsea a few years ago.
It is closely related to bladder campion, Janey - that's Silene vulgaris.

I'm always a bit cautious of perennials which spread underground... sometimes I haven't realised till after I've planted a shrub, and find it sending out shoots in all directions....
... there should be a warning on the labels !!!

I agree with that, Terra. I have the same problem with Lysimachia 'Firecracker'. The garden correspondent on the Telegraph says this Silene is easily controlled - HA!!!