They look like early new growth on Lychnis coronaria.

I agree...and very hardy..long flowering,and I still have some on mine.You just need to snip of the long stems..They will be lovely next year,Gg :o)

I also agree

Rose campion, to give the common name. Where the pink/white flower was is now a seed head with 1-3 black seeds. You can put them in the ground now if want more. They prefer full sun, growing toward the light if not and prone to looking a bit messy if so! Some self seeded in an east facing border and did just that while the ones in the south facing went straight and produced lots of branchy growth and flowers. I think it goes well with Sea Holly/Eryngium and purple Alliums.

You don't mean something I'd actually quite like has self-seeded into my garden do you?! Yes! I'm quite happy about this :o))) It must've come from my neighbours garden. I think I'll re-locate it to somewhere with a bit more space and sun in the back garden. Thank you all :-)

It's nice to get a freebie that you like,Gg..and agree,full sun is best....I would leave them where they are till next spring..they look happy enough..dead heading on a regular basis,will keep them going all summer..mine have been flowering since May..easy to split too,if you want more :o)

Collect the seeds and scatter them where you would like some more or sow them in a pot. This plant looks stunning en masse!