I have this and love it to bits. As tough as old boots, seeds everywhere so you can transplant to wherever you need a bit of colour and you can dig it up easily to get rid when you're fed up with it. It does all that in my garden but may behave differently in yours
No idea Nut - I don't usually remember these things, but we had loads of this outside the office where I used to work and every summer colleagues would ask me what it was. It was no good telling them it was Lychnis as they'd look it up and tell me I was wrong so I had to remember Silene
“I am not lost, for I know where I am. But however, where I am may be lost.” Winnie the Pooh
Posts
I agree with Edd
but it's now known as Silene coronaria 
I have this and love it to bits. As tough as old boots, seeds everywhere so you can transplant to wherever you need a bit of colour and you can dig it up easily to get rid when you're fed up with it. It does all that in my garden but may behave differently in yours
Is it silene now
I hadn't registered that. What else has changed?
In the sticks near Peterborough
Ah! thanks everyone. odly enough i might trasplant to my wild medow area as it needs some colour like this.
No idea Nut - I don't usually remember these things, but we had loads of this outside the office where I used to work and every summer colleagues would ask me what it was. It was no good telling them it was Lychnis as they'd look it up and tell me I was wrong
so I had to remember Silene
I used to keep up with all those changes
In the sticks near Peterborough
I do remember geranium/pelargonium ... that's probably a triumph