I still lean towards a Lychnis...but the leaves aren't quite right.
I hope someone else will recognise it. It's not one of the more common ones, so I could be well off-beam here. Sorry not to have a definite ID for you.

Thanks, I hope someone can help?

I'm sure they will - Bamboo and Fractal are really good at IDs. Give them a while to see it.

I think if you look closely this might be 2 plants? such as a Lychnis chalcedonica in among a young eucalyptus?

No its just the one plant, there are about 6 of them in my garden

The colour is like that of Silene armeria, but the flowers are not quite right for that.

I think thats correct, looks like it is that , so its a wildflower right? Still looks very pretty so it can stay. Thanks to all

If it is the Silene armeria it is a winter hardy annual. It self seeds and survives over winter to flower next season. Not native to Britain,

So that's why I thought it might be a Silene! It is! Thanks, Ob.