What’s this plant?

squirral87k4-WvGwT

Does anyone know what this herbaceous plant is called?

It produces small lilac flowers in the summer. 

The leaves are much larger than the flowers and it’s very vigorous. It’s chocked out some lily bulbs and seems to thrive on neglect. 

YMK

It looks like Japanese Anemone 

Dovefromabove

Another vote her for Japanese Anemone. Can be a useful plant for shade, but it needs reminding who’s in charge from time to time 😉 

Busy-Lizzie

When I saw this post last night I thought Japanese Anemone too, but I didn't answer because of the small purple flowers. My three have quite big flowers, light pink, dark pink and white.
Like these -

Papi Jo

squirral87k4-WvGwT said:

[...]
It produces small lilac flowers in the summer. 

[...]

That is quite vague. What do you call "small"? 1mm / 1cm / 1in / ?

Fairygirl

Yes - pinks and whites for Jap. anemones, as @Busy-Lizzie says, but many of the whites look quite lilac in bud, and also have a lilac tint on the reverse of the petals, so maybe that's what the OP means?

There looks as if there are buds appearing in the first pic though. It seems early for them, but we're a bit later than many areas - July into August for them here.  

squirral87k4-WvGwT

Thank you all. The flowers do look like the Japanese anemone I’ve just seen online so it must be that.

@Papi Jo “small flowers” is very vague - I meant small relative to the size of the leaves.

@Dovefromabove spot on. It’s chocked out the lillies planted around it! 

@Fairygirl - I’m in the SE and it’s in a warm spot right up against the front of the house so perhaps it flowers earlier here. 

Fairygirl

They can be quite invasive in certain conditions - especially the pink ones. They're less bothered by hotter, drier spells than the whites too.