Isn't it an Aster? Looks like a Michaelmas daisy to me

Maybe a Stokes' Aster (Stokesia laevis)?

Thank you both. The leaves are certainly 'starry', so I think Stokesia laevis is right!

Not so sure - don't they have spiky ends to the petals?

You know more than me, Sue . . I'm not sure now!

The flower buds that I can see to the lower left reminded me of Stokesia.

Not so Sheila, I looked them up on Google. Have a look they are very pretty.

True enough, Stera! Stokesias have broader petals than the picture, with divided tips. I guess that it's an Aster then, maybe 'Wood's Blue', or one of it's kin?

I'm grateful to you both for taking such trouble. What did you look up on Google, Sue?! I've just added another photo - trying to show its habit, which is very different from my other Asters. This is quite a 'royal' blue and is only about 12" tall.

P.S. Just tried 'royal blue Aster' on Google and it looks very like Aster Novi-Belgii (which actually does sound familiar) :))

I just put in Stokesia laevis Sheila. I tried to enlarge your photo but when it got big enough to be sure it went a bit blurry. Anyway its very pretty, which is what really matters - a rose by any other name- or is that heresy?
Nova Belgii is pretty tall - mine is at least 4 feet.

Oh wow - how long have you had yours, Sue? I think this plant is only 2 years old . . .

Hah! 'Wood's Blue is the one I remember, but Aster nova-angliae 'Purple Dome" is a better match.

Thanks again Tug - you certainly know your Asters. Yes, purple dome is a perfect match :))

Probably 5 or six years Sheila but the flowers were as tall as that from the start.

There are SO MANY different Asters . . . no wonder they're not so easy to identify.